U.S. patent application number 11/731499 was filed with the patent office on 2008-10-02 for method and system for providing loitering trace in virtual machines.
This patent application is currently assigned to SAP AG. Invention is credited to Oliver Bendig, Ralf Schmelter, Michael Wintergerst, Arno Zeller.
Application Number | 20080243970 11/731499 |
Document ID | / |
Family ID | 39796169 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080243970 |
Kind Code |
A1 |
Schmelter; Ralf ; et
al. |
October 2, 2008 |
Method and system for providing loitering trace in virtual
machines
Abstract
A system and method are provided for performing loitering trace
in virtual machines. In one embodiment, status of objects in a
garbage collection heap at a first virtual machine at a server is
identified, in response to a memory leak. First objects that are
used are identified. Second objects that are alive and not being
used are identified. Information regarding the first objects and
the second objects is communicated to a second virtual machine at a
client.
Inventors: |
Schmelter; Ralf; (Wiesloch,
DE) ; Wintergerst; Michael; (Rauenberg, DE) ;
Zeller; Arno; (Mannheim, DE) ; Bendig; Oliver;
(Karisdorf-Neuthard, DE) |
Correspondence
Address: |
SAP/BSTZ;BLAKELY SOKOLOFF TAYLOR & ZAFMAN LLP
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Assignee: |
SAP AG
|
Family ID: |
39796169 |
Appl. No.: |
11/731499 |
Filed: |
March 30, 2007 |
Current U.S.
Class: |
1/1 ;
707/999.206 |
Current CPC
Class: |
G06F 2201/865 20130101;
G06F 12/0253 20130101; G06F 11/3466 20130101 |
Class at
Publication: |
707/206 |
International
Class: |
G06F 12/00 20060101
G06F012/00 |
Claims
1. A method comprising: identifying status of objects in a garbage
collection heap at a first virtual machine at a server, in response
to a memory leak; identifying first objects that are being used;
identifying second objects that are alive and not being used;
communicating a report having information relating to the first
objects and the second objects to a second virtual machine at a
client.
2. The method of claim 1, further comprising generating the report
having the information relating to the first objects and the second
objects.
3. The method of claim 1, further comprising removing the second
objects that are alive and not being used.
4. The method of claim 1, further comprising preserving the first
objects that are being used, the first objects are alive.
5. The method of claim 1, wherein the garbage collection heap
includes a Java garbage collection heap.
6. The method of claim 1, wherein the server comprises a Java
application server having a Java 2 Enterprise Edition (J2EE)
engine, the J2EE engine having the first virtual machine, the first
virtual machine including a first Java virtual machine.
7. The method of claim 1, wherein the second virtual machine
comprises a second Java virtual machine.
8. A system comprising: a server having a first virtual machine,
the first virtual machine having a profiling infrastructure, the
profiling infrastructure to identify status of objects in a garbage
collection heap at a first virtual machine at a server, in response
to a memory leak, identify first objects that are being used,
identify second objects that are alive and not being used,
communicate a report having information regarding the removing of
the first objects and the second objects to a second virtual
machine at a client; and a client coupled with the server, the
client having a second virtual machine to receive the report from
the first virtual machine at the server.
9. The system of claim 8, wherein the profiling infrastructure is
further to generate the report having the information relating to
the first objects and the second objects.
10. The system of claim 8, wherein the server to remove the second
objects that are alive and not being used.
11. The system of claim 8, wherein the server to preserve the first
objects that are being used, the first objects are alive.
12. The system of claim 8, wherein the garbage collection heap
includes a Java garbage collection heap.
13. The system of claim 8, wherein the server comprises a Java
application server having a Java 2 Enterprise Edition (J2EE)
engine, the J2EE engine having the first virtual machine, the first
virtual machine including a first Java virtual machine.
14. The system of claim 8, wherein the second virtual machine
comprises a second Java virtual machine.
15. A machine-readable medium comprising instructions, which when
executed, cause the machine to: identify status of objects in a
garbage collection heap at a first virtual machine at a server, in
response to a memory leak; identify first objects that are used;
identify second objects that are alive and not being used;
communicate information regarding the removing of the first objects
and the second objects to a second virtual machine at a client.
16. The machine-readable medium of claim 15, wherein the
instructions when executed, further cause the machine to generate
the report having the information relating to the first objects and
the second objects.
17. The machine-readable medium of claim 15, wherein the
instructions when executed, further cause the machine to remove the
second objects that are alive and not being used.
18. The machine-readable medium of claim 15, wherein the
instructions when executed, further cause the machine to preserve
the first objects that are being used, the first objects are
alive.
19. The machine-readable medium of claim 15, wherein the
information includes information regarding the third objects being
preserved in the heap.
20. The machine-readable medium of claim 15, wherein the garbage
collection heap includes a Java garbage collection heap.
Description
FIELD
[0001] Embodiments of the invention relate generally to the field
of data processing systems. More particularly, the embodiments of
the invention relate to provide loitering trace in virtual
machines.
BACKGROUND
[0002] A memory on any computing system is a limited resource. No
matter how fast computing systems become, they always depend upon a
finite amount of memory in which to run their software
applications. As a result, software developers should consider this
resource when writing and developing software applications.
[0003] The Java programming language differs from many traditional
programming languages (e.g., C, C++) by the way in which memory is
allocated and deallocated. In languages like C and C++, memory is
explicitly allocated and deallocated by the application
programmer/developer. This can greatly increase the time spent by
programmers in tracking down coding defects in regards to
deallocating memory. The Java programming language presents several
features that appeal to developers of large-scale distributed
systems, such as "write once, run anywhere" portability, portable
support for multithreaded programming, support for distributed
programming, including remote method invocation, garbage
collection, and an appealing object model have encouraged Java use
for systems with a size and complexity far beyond small applets.
However, the developers of these applications often encounter
problems, such as memory leaks, performance and scalability
problems, synchronization problems, and programming errors.
[0004] Java runtime environments (e.g., Java virtual machine)
provide a built-in mechanism for allocating and deallocating
memory. In Java, memory is allocated to objects. The Java virtual
machine ("VM" or "JVM") automatically handles the amount and
allocation of memory upon an object's creation. The Java runtime
environment employs a "garbage collector" (GC) to reclaim the
memory allocated to an object that is no longer needed. Once the GC
determines that the object is no longer accessible (e.g., when
there is no longer any references to it stored in any variables,
the fields of objects, or the elements of any arrays, etc.), it
reclaims the allocated memory. When objects in a Java application
are no longer referenced, the heap space the object occupied is to
be recycled so that the space becomes available for
subsequently-created objects.
[0005] Although having garbage collection improves productivity, it
is not entirely immune from a class of bugs, called "memory leaks."
A memory leak can occur when a program (or in the case of Java, the
VM) allocates memory to an object but never (or only partially)
deallocates the memory when the object is no longer needed. As a
result, a continually increasing block of memory may be allocated
to the object, eventually resulting in an "Out Of Memory Error"
(OOME). In other words, a memory leak occurs when memory is
allocated, but it is never (or only partially) reclaimed. Memory
leaks can also occur when a data structure (e.g., hashtable) is
used to associated one object with another and even when neither
object is required any longer, the association with the data
structure remains, preventing the objects from being reclaims until
the data structure is reclaimed. Stated differently, when a
lifetime of the data structure is longer than that of the objects
associated with it, memory leaks are caused.
[0006] Memory leaks are of particular concern on Java-based systems
(e.g., Java 2 Platform Enterprise Edition (J2EE) platforms) which
are to run twenty-four hours a day, seven days a week. In this
case, memory leaks, even seemingly insignificant ones, can become a
major problem. Even the smallest memory leak in code that runs 24/7
may eventually cause an OOME, which can bring down the VM and its
applications or even all VMs running on a particular application
server instance. This can cause critical performance problems.
[0007] It is generally preferred to profile memory use and debug
memory leaks in an application code in the early stages of
development to provide an early detection of memory problems long
before the production stage. Although garbage collection makes code
much safer, because having the developer to explicitly delete
objects from memory is prone to human error, garbage collection is
not a panacea. For example, if the developer does not manage the
references to the Java objects carefully, it can result in a memory
leak problem, such as a reference to an object is stored within an
instance or class field, this reference may exist throughout the
life of the application and, unless desired, is regarded a memory
leak.
[0008] Within a distributed application server environment having
thousand of concurrent users, performance and scalability problems
are typical. The causes of problems are various, such as
synchronization problems, extensive access to shared resources
(e.g., database systems), bad configuration settings, etc. To
provide consistency within such a system, locks with various
validity scopes (e.g., VM-local, application-server-wide, and
system-wide) are used; however, deadlock situations and
synchronization problems exist.
[0009] Several performance monitoring, profiling, and debugging
tools are used to examine software applications to determine
resource consumption within the Java runtime environment (JRE). For
example, a profiling tool may identify the most frequently executed
methods and objects created in an application. A type of software
performance and debugging tool is a "tracer." However, such tools
are very limited in detecting and exposing system inefficiencies
and problems (e.g., memory leaks), while consuming great amounts of
system resources by requiring overhead tasks, such as starting and
restarting of VMs in special modes. Further, such tools are also
limited in providing necessary information about system problems
and the limited information that these tools may provide is not
useful for applications comprising several thousand objects. This
leaves developers with often insurmountable amounts of code to
manually evaluate to track down the problem objects/variables, such
as the specific class, method calls, etc. For example, conventional
profiling tools, like Optimizelt and JProbe, when used, require
restarting of VMs and servers, which results in loss of production
and system resources, particularly when restarting a productive
system. Moreover, the starting of a server and its VMs further adds
to the system overhead by increasing memory consumption, which also
harms the normal work of the server and server software. The
restarting of the server adds overhead in regards to the Central
Processing Unit (CPU), as the server would have to start up from
scratch.
[0010] Memory leaks can occur for various reasons, such as due to a
clean-up operation failure at a cache that can cause memory leaks.
No conventional methods or systems provide for detection of entries
or object resulting from the operation failure that cause such
memory leaks or the time period during which these entries or
objects are used.
[0011] FIG. 1 illustrates a conventional profiling tool. Client 102
is in communication with server 108. Client 102 includes a VM 102.
Server 108 includes a VM 112, which includes Java Virtual Machine
Profiling Interface (JVMPI)-based interface 116 and implementation
114. Server 108 further includes a native/default profiling agent
(having an agent library) 110 which is plugged into the VM 112 at
start-up. Since JVMPI is a native/default-interface, the agent 110
is also written in native code. An agent 110 refers to a software
entity, which is used to gather profiling information native VM
interfaces (e.g., JVMPI). JVMPI-based implementation 114 suffers
from high memory footprints and, like conventional tools JProbe and
Wily Introscope, requires a VM restart. However, conventional
profiling tools (e.g., also those using Java Virtual Machine Tool
Interface (JVMTI)) cannot be used in productive systems without
disturbing user sessions. Further, they cannot be used in large
application server environments as they cause high memory
consumption. Referring back to FIG. 1, for example, to start
profiling traces, the VM 112 is to be restarted in special way,
such as by having the agent 110 loaded at VM-startup, which can
cause negative impact on performance and memory consumption. There
are merely some of the limitations of conventional profiling
solutions. Similarly, conventional monitoring tools and debugging
tools (e.g., using Java Virtual Machine Debugging Interface
(JVMDI)) also suffer from these and additional limitations.
SUMMARY
[0012] A system and method are provided for performing loitering
trace in virtual machines. In one embodiment, status of objects in
a garbage collection heap at a first virtual machine at a server is
identified, in response to a memory leak. First objects that are
used are identified. Second objects that are alive and not being
used are identified. Information regarding the first objects and
the second objects is communicated to a second virtual machine at a
client.
[0013] The above attributes may be implemented using a computer
program, a method, a system or apparatus, or any combination of
computer programs, methods, or systems. These and other details of
one or more embodiments of the invention are set forth in the
accompanying drawings and in the description below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention is illustrated by way of example and not by
way of limitation in the figures of the accompanying drawings in
which like references indicate similar elements. It should be noted
that references to "an" or "one" embodiment in this disclosure are
not necessarily to the same embodiment, and such references mean at
least one.
[0015] FIG. 1 illustrates a conventional profiling tool.
[0016] FIG. 2 illustrates an embodiment of a server having an
embodiment of an on-demand profiling infrastructure.
[0017] FIG. 3 illustrates an embodiment of a backend VM having an
embodiment of an on-demand profiling infrastructure.
[0018] FIG. 4 illustrates an embodiment of a process for profiling
using an embodiment of an on-demand profiling infrastructure.
[0019] FIG. 5 illustrates an embodiment of a mechanism for
performing loitering trace at a virtual machine.
[0020] FIG. 6 illustrates an embodiment of a transaction sequence
for performing loitering trace.
[0021] FIG. 7 illustrates an embodiment of a process for performing
loitering trace.
[0022] FIG. 8 illustrates an embodiment of a monitoring tool.
[0023] FIG. 9 illustrates an embodiment of a computing system.
[0024] FIG. 10 illustrates an embodiment of a client/server network
system employing a message enhancement mechanism.
DETAILED DESCRIPTION
[0025] As used herein, references to one or more "embodiments" are
understood as describing a particular feature, structure, or
characteristic included in at least one implementation of the
invention. Thus, phrases such as "in one embodiment" or "in an
alternate embodiment" appearing herein describe various embodiments
and implementations of the invention, and do not necessarily all
refer to the same embodiment. However, they are also not
necessarily mutually exclusive. Descriptions of certain details and
implementations follow, including a description of the figures,
which may depict some or all of the embodiments described below, as
well as discussing other potential embodiments or implementations
of the inventive concepts presented herein.
[0026] Java applications can vary in both size and complexity. In
addition, certain large Java application (e.g., .about.10,000
classes and .about.1,000,000 methods with .about.100,000,000 method
calls) may run 24/7 ("long living" applications). Within a long
living application, major problems (e.g., memory leaks) are
expected to occur in terms of both stability and performance. For
example, a single long living object that increases in size by 1
byte between each GC cycle will eventually cause the application
and VM to crash due to an OOME. Although such a crash may take a
long time (e.g., 1 bytes per GC cycle*millions of free bytes of
memory), it will inevitably occur. Furthermore, when dealing with
such long applications and productive systems, mere use of
commercial and non-commercial conventional profiling tools and
debugging tools having JVMPI and JVMTI profiling interfaces and
JVMDI debugging interface, respectively, are not suitable and
cannot provide the necessary profiling, debugging, and monitoring
information. Even when dealing with suitable systems, such
conventional tools cause high memory footprints and are not
effective without having to restart the VM and are known to disturb
user sessions inherent to the VM.
[0027] In one embodiment, a vendor-specific proprietary interface
and implementation are provided, as described throughout this
document (e.g., see FIG. 1). This implementation can be made an
integral part of a VM (e.g., JVM, SAP JVM) and allow for on-demand
examining of system problems, including in productive systems,
without restarting the underlying VM. These system problems can
range anywhere from memory leaks to performance, scalability and
synchronization problems. In one embodiment, "on-demand" refers to
examining (e.g., profiling, tracing, debugging, and/or monitoring)
system problems in runtime, such as without the need for restarting
the underlying VM.
[0028] FIG. 2 illustrates an embodiment of a server 202 having an
embodiment of an on-demand profiling infrastructure 208. Sever 202
comprises a backend VM 206 (e.g., JVM, SAP JVM) having an
embodiment of an on-demand profiling framework or infrastructure
(profiling infrastructure) 208. Profiling infrastructure 208 is
shown in communication with a server Java application programming
interface (API) 204. In one embodiment, profiling infrastructure
208 is implemented as an intrinsic and direct part of the
underlying VM 206 and is embedded within the backend VM 206, rather
than relying on native profiling interfaces, such as JVMTI and
JVMPI, and agent, for implementation. Since the profiling
infrastructure 208 is an intrinsic part of the backend VM 206, no
additional memory overhead is needed. Java API 204 allows for
starting and stopping of the profiling backend VM 206. In one
embodiment, backend VM 206 (e.g., Java VM) resides at server 202
(e.g., J2EE server).
[0029] In one embodiment, profiling is performed using profiling
infrastructure 208 that resides at backend VM 206 that is being
profiled. Profiling infrastructure 208 includes a number of
components (as described in FIG. 3) to perform trace profiling. In
one embodiment, using profiling infrastructure 208, no default
profiling agent or default implementations and instances (e.g.,
JVMPI, JVMTI) are needed or employed. Without having the default
agent employed, a direct communication is established between
backend VM 206 and frontend VM 214 via server Java API 204 and
client Java API 212 and profiling protocol 210. Any number of VMs
may be used as backend or frontend VMs. Furthermore, when
performing profiling trace in an offline profiling mode, an
external profiling file 218 is used to store profiling trace data.
Starting and stopping of profiling trace may be performed in a
number of ways, such as using a Graphical User Interface
(GUI)-based monitoring tool 220. The profiling data is written
using various components of profiling infrastructure 208 and
displayed to the user using any number of display devices. These
display devices may include GUI-based display devices. In one
embodiment, using profiling infrastructure 208, on-demand profiling
is performed which refers to performing the profiling without
restarting the underlying VM 206. Stated differently, the profiling
is performed in runtime without any interruptions or restarting of
the underlying VM 206.
[0030] Profiling infrastructure 208 can be used for starting
profiling traces for certain users or applications, such as using
profiling annotations. Profiling annotations refer to a concept of
tagging threads with certain semantic information from an
application server environment. Here, Java API 204 is provided
which allows for annotating a Java thread with one or more of the
following information: user name, application name, request
identifier, and session identifier. If profiling traces are
started, a thread filter for such information is provided and thus,
a profiling trace can be started only a certain user or
application. A Java API is also provided on the client-side, such
as client Java API 212, that communication with server Java API 204
via a profiling protocol 210. Client 216 includes frontend VM 214,
which includes any arbitrary VM that represents a native
application that speaks (e.g., in case of online profiling) the
profiling protocol 210 and/or knows (e.g., in case of offline
profiling) the profiling file format of profiling file 218. Backend
VM 206 is the one that is being profiled.
[0031] It is to be noted that the VMs 206, 214 may not be VMs and
instead be any program or application (e.g., a native application
or program) that is compatible with the components of and related
to the profiling infrastructure 208. For example, the frontend VM
214 is illustrated here merely as an example for brevity and
clarity. It is, however, contemplated that a frontend VM 214 or any
VM for that matter is not necessary for embodiments of the present
invention. For example, in one embodiment, instead of employing a
VM 214, any program or application that is compatible with the
mechanisms and components described herein is acceptable and
functional and can be employed and implemented. Stated differently,
for example, any program that can read and speak the described
components (e.g., components of profiling infrastructure 208),
protocols (e.g., socket communication protocol), APIs (e.g.,
server- and client-side APIs 204, 212), parameters, profiling files
218, etc., is compatible and can be used instead of a VM, such as
the frontend VM 214. This is applicable throughout this document
wherever there is mention of a VM 206, 214.
[0032] The illustrated mechanism 200 provides both an online
mechanism for (interactive) profiling and an offline mechanism for
(non-interactive) profiling. When starting profiling the backend VM
206, any profiling parameters including the desired mode, e.g., an
online or offline mode, are specified. If started in the online
mode, the profiling backend VM 206 opens a port and waits for a
connection. The profiling frontend VM 214 attach to this connection
via the profiling protocol 210 and Java APIs 204, 212. The
starting, running, and stopping of profiling and tracing is then
performed. In one embodiment, online profiling is performed via
internal components, such as Java APIs 204, 212, or external
components, such as a monitoring tool (e.g., Java VM monitor) 220.
Online profiling may also be performed using a command line, such
as java -agentlib:jdwp,transport=dt_socket, address=8000,suspend=n
or bin/java -monjdwp:transport=dt_socket,address=8000,server=y. For
the offline mode, profiling files 218 are used to store profiling
data and a special interface is provided to couple the backend VM
206 with the frontend VM 214 via client Java API 212 to allow for
starting and stopping of traces. In some cases, server Java API 204
can also be used to perform offline profiling. Offline profiling
may also be performed using monitoring tool 220 and/or using a
command line, such as java -XX: +Profiling
-XX:+ProfilingAlloationTrace.
[0033] When the profiling mechanism 200 is started in the offline
or non-interactive mode, the profiling information is stored in an
external medium 218 (e.g., file system) and can be analyzed after
the profiling run. This way, the profiling information may then be
used for port-mortem analysis; however, traces can still be started
and stopped in an interactive manner. In contrast, the online or
interactive mode allows for analyzing the profiling information
online. For example, if a class statistic trace has been enabled
and a garbage collection happens, the profiling information can be
directly accessible through a stream-based interface.
[0034] Furthermore, to have no performance degradation in case of
running in a non-profiling mode (e.g., when no profiling is being
performed), VM 206 may maintain a global flag indicating whether
profiling is enabled or not. The flag may be requested each time
any profiling data is written. For example, a profiling trace for
garbage collection events may be implemented in the following way:
when a garbage collection is performed, the global profiling flag
is checked. If profiling is enabled, the flag is checked to
indicate whether garbage collection events are to be profiled. This
can also be done via some VM global flags. If the garbage
collection trace is enabled, the backend VM 206 may be called to
collect the desired data.
[0035] FIG. 3 illustrates an embodiment of a backend VM 206 having
an embodiment of an on-demand profiling infrastructure 208. In one
embodiment, profiling infrastructure 208 contains controller
framework 302, thread filter 304, buffer framework 306, class
filter 308, identification service 310, communication framework
312, object identification service 314, allocation trace module
316, loitering trace module 318, garbage collection trace module
320, and other trace modules 322 to perform other traces.
[0036] In one embodiment, profiling controller framework 302 is
used for starting and stopping profiling runs and traces.
Controller framework 302 allows the user to specify profiling
options or settings that the user would want to enable. These
profiling settings to be applied are divided into distinct areas,
such as functional profiling settings and filter settings. The
functional profiling settings determine the area to be profiled
(e.g., allocation trace, reference trace, etc.), while the filter
settings define the validity scope (e.g., user, session, thread,
VM, etc.) of the functional profiling settings. For example, an
allocation trace can be started for a specified user. Java API and
graphical user interface (GUI) are provided in communication with
profiling controller framework 302. GUI is used to enable the user
to directly specify the desired profiling settings without any
system-guidance. Additionally, a wizard-similar interface is
provided. GUI also allows for an expert mode and for a
wizard-guided mode. Controller framework 302 may include a
profiling evaluation module for analyzing a performed profiling
run. For example, the Java API can be used for getting the complete
low-level profiling information gathered within a corresponding
profiling run as well as for getting condensed, problem-oriented
profiling information. The condensed profiling information may be
used to directly pinpoint various problematic areas. For example,
if the user has performed performance analysis using a time-based
sampling approach, the Java API may enable a client to directly
receive information about the time-consuming methods. The user may
view this information via GUI at a display device at the
client.
[0037] Controller framework 302 is used for starting and stopping
profiling runs and traces, which includes starting and stopping
various profiling options (further described later). For each
profiling run the user is free to determine the set of traces to be
started. For example, the user may start an allocation trace using
the allocation trace module 316 together with a class statistic
trace. A user-defined name may be assigned to each non-interactive
profiling run and used later on to evaluate the gathered profiling
information. Considering interactive profiling runs, the user is
able to evaluate the profiling information online and therefore,
the profiling information may be available through a stream-based
interface.
[0038] Furthermore, controller framework 302 may be independent of
the surrounding application server environment. Stated differently,
controller framework 302 refers to the underlying VM 206 currently
executing a profiling request (e.g., starting an allocation trace).
The corresponding application server infrastructure may be
responsible for starting and stopping the desired trace on other
VMs. For example, if an allocation trace is started for a certain
user session at VM 208, the application server infrastructure
accounts for starting the allocation trace in the VMs executing
requests for the user session. Controller framework 302 enables the
application server infrastructure to specify thread filters 304. A
thread filter 304 may contain the following information: client,
user, session identifier, request identifier, application name, and
component name. On the one hand, controller framework 302 may
provide a facility to tag these pieces of information to a thread.
On the other hand, if a certain profiling run is to be started, a
thread filter 304 is provided. Hence, for example, a trace may be
stared only for a certain user. Accordingly, the application server
is responsible for setting the current thread state (e.g., client,
user, session identifier, etc.). In one embodiment, an application
server includes a J2EE server.
[0039] In one embodiment, the profiling options include
functions/cases, such as memory debugging (e.g., memory leak
detection), performance analysis, synchronization monitoring, and
application debugging (e.g., detecting called methods). These
profiling functions further include a number of sub-functions, such
as heap dump, coupling of debugging and profiling infrastructure,
time-based sampling, memory-based sampling, method statistic,
allocation trace, silent allocation trace, allocation statistic
trace, loitering trace, garbage collection trace, garbage
collection statistic, class statistic trace, permanent generation
statistic trace, local garbage collection trace, other traces, such
as reference trace, object death trace, object movement trace,
global reference trace, method trace, time method trace,
input/output (I/O) trace, monitor trace, shared lock trace, method
count trace, execution line trace, scheduler trace, and exception
trace.
[0040] Solving a memory leak problem may include a couple of
processes, such as identifying the Java classes or objects caused
the memory leak, and determining where in the infrastructure or
application code the leak occurred. Many of the sub functions can
be used to solve memory leak problems. Class statistic trace
functionality is provided to help identify the Java classes that
cause memory leaks. Class statistic trace includes getting an
overview of all living classes within particular VM, including
class name, class loader description, the number of object
instances, and the accumulated net and gross size of all object
instances. The information may be traced after each full local
garbage collection. Reference trace includes detecting the objects
holding references to leaking objects. It also provides the
complete reference chain to a specific object instance. This
information may also be available after one full local garbage
collection.
[0041] If the class statistic trace reveals that specific objects
are created over and over again, using the allocation trace module
316, the allocation trace may be enabled to check for the exact
allocation place. Using the allocation trace module 316, the
allocation trace enables the user to specify a class filter 308.
Silent allocation trace is a derivate of allocation trace. When an
allocation trace is started, each object, which is allocated and
adheres to a user-defined class filter 308, is assigned to an
object identifier. Although the allocation trace enables the user
to get informed about object allocations; the user may not get the
information when the corresponding object dies. In that case,
object death trace allows the user to check for those objects are
garbage collected and no longer alive. Object movement trace makes
allows the checking of why certain objects are kept alive, while
the allocation trace allows for getting information when certain
objects are created.
[0042] In some cases, memory leaks occur due to the fact that a
failed clean-up operation. For example, considering a, at regular
intervals, the cache might be cleared. If the clean-up operation
were interrupted at the end of the operation (e.g., due to a VM
abort exception), most cache entries would probably be deleted;
however, some entries might still exist. Thus, a memory leak may be
resulted if the cache were not able to remove any of the existing
entries. The detection of this kind of memory leak could be
difficult, since most object instances of the corresponding class
are removed and merely a few exist. Thus, class statistic trace may
not be the right choice to detect such a memory leak. One
characteristic of this problem is that the memory leak is caused by
objects which may not be used any longer. The loitering trace
performed via loitering trace module 318 facilitates the detection
of objects which are not used for a long time.
[0043] Various performance problems may be caused by any number of
reasons, such as choosing the wrong algorithm for a problem,
repeatedly recalculating the same result, excessive allocating of
temporary objects, too many I/O operations or transferring too much
memory, etc. Profiling helps improving the performance by
determining what is it that is to be optimized. Profiling
identifies parts of the overall system for which optimization can
have an impact on the overall performance. Optimizing a function
which only amounts to a miniscule fraction of the overall runtime
may not have noticeable benefits. Profiling also determines how the
optimization is to be done. Checking for optimization options of
those parts that are identified during the first process.
Time-based sampling is used to get an overview of methods, which
consume the most CPU resources of the application. Time-based
sampling works by dumping a stack trace of the currently active
thread at regular intervals. Memory-based sampling works
analogously to the time-base sampling; however instead of dumping a
stack trace in time intervals (.DELTA.t), stack trace is sampled
after an amount of memory (.mu.M) is allocated on the Java heap.
This way, those methods that allocate the largest number of bytes
on the Java heap are identified.
[0044] When time-based sampling shows that a method uses a large
amount of time, the reason for this resource consumption might be
that a call of the method is expensive or the method is called very
often. To find out how many times a particular method was called,
method statistic trace may be used. Together with time-based
sampling, method statistic trace may also allow for calculating the
average runtime of a specific method (e.g., the "cumulative time"
divided by the method count). Method trace is used to get more
detailed information than method statistic. Time method trace can
be used to provide very detailed trace information. Time method
trace provides for detecting method calls that (for any number of
reasons) take a particularly long time. To see, if garbage
collection is properly configured or if a particular problem
related to garbage collection exists, local GC statistic is used,
which includes dumping a statistical entry for each local garbage
collection (partial and full) for each garbage collection run.
[0045] Another source of performance problems is related to I/O.
These I/O-related problems include a network connection being
operated at its bandwidth maximum, the latency being too high, an
external system being overloaded, etc. To check for an I/O problem,
I/O trace allows for tracing the timing of each I/O operation. I/O
trace can be used in analysis to check for operations, where huge
amounts of data were transmitted, the I/O operation took an
extraordinary amount of time, or a huge amount of small I/O
operations was performed.
[0046] Java has an explicit support for multithreading and
concurrency at the language level. Although these welcome features,
the typical problems with multithreading and concurrency are
deadlocks, race conditions, thread starvation, and scalability
problems. Synchronization monitoring is provided to detect such
problems. For example, synchronization monitoring includes monitor
trace that identifies deadlock or scalability problems and gathers
information about locks used inside a VM. To find synchronization
problems, a thread trying to acquire a lock is identified and once
it is identified, the lock is freed by the thread. Shared lock
trace is used to identify deadlocks between VMs and scalability
problems of a server instance. Shared lock trace provides
information about different kinds of shared lock activities, like
entering and leaving. Further, for such problems above, scheduler
trace is used to know why a thread was scheduled and why it gave up
control of the CPU, and for how long the entire VM was waiting on
external I/O or just sleeping.
[0047] In one embodiment, application debugging is used to provide
those the debugging functionalities that are not supported by
conventional debugging instances and protocols, such as JVMDI, Java
Debug Wire Protocol (JDWP), etc. For example, application debugging
covers functionalities, such as call coverage and line coverage.
Regarding call coverage, method count trace may deliver a number of
calls to a method. Regarding line coverage, execution line trace
may deliver information about code lines that were executed. Method
call trace is used to find all methods that are called. When the
method call trace is enabled, the VM 206 counts method calls and
when the method call trace is disabled, the VM 206 dumps the
collected information, such as name and signature of a method and
the number of times it was called. Execution line trace may be used
to find out the lines of code that are not executed. When the
execution line trace is triggered, it enables the VM to write out
information about the method and code line each time a byte code is
interpreted and/or the line number changes. Such information can
help the developer find out the lines of code that are not covered
particular test cases.
[0048] Method trace may be employed to trace or profile the
debugging process of an application. For example, the method trace
is used to find out what has happened before the program reaches a
certain point. Such information may be used to trace back the
program flow and find out in which way the program reached that
point of code. Exception trace is another functionality that may be
employed to trace or profile the debugging process of an
application. This information can be used to trace back the reasons
for exceptions that followed up and for different execution
branches.
[0049] In one embodiment, a dedicated Java API and a GUI is
provided to allow for starting and stopping of various
functionalities and uses (e.g., allocation trace, loitering trace,
GC trace, and other traces) and for getting the corresponding
profiling and tracing results. To determine and analyze the
profiling and tracing results, an expert mode and/or a guided mode
are provided. For example, a guided mode may directly pinpoint any
problem areas.
[0050] Profiling infrastructure 208 is compatible with multiple
clients. For example, depending on the surrounding application
server infrastructure and whether any clients are handled in a
special way, the profiling infrastructure 208 may perform in
compliance with several clients, simultaneously, and remain
multiple client-compliant. Profiling infrastructure 208 also allows
for restricting profiling runs to certain clients, while the
surrounding application server environment may assure that the
current client information is assigned to the respective thread.
Furthermore, profiling infrastructure 208 may be started on-demand,
which includes performing profiling infrastructure functionalities
(e.g., profiling, tracing, etc.) without restarting the entire
application server or even the underlying VM 206. If no profiling
option is enabled by a certain user, there is no impact on the
response time caused by the profiling infrastructure 208. However,
if profiling is enabled, it may depend on the started profiling
options and filter settings about how the overall system
performance is influenced. For example, if a method trace is
started on an application server without any filter settings (e.g.,
user, classes, etc.), the performance may decrease to an extent.
Therefore, the profiling infrastructure 208 as well as the
application server infrastructure must provide options to restrict
profiling runs. This way, profiling may be enabled for a particular
user or session, while users and sessions remain unaffected. In
addition, profiling infrastructure 208 provides reasonable and
necessary filter settings for various profiling traces.
[0051] Class filters 308 are implemented to allow for limiting
profiling trace outputs by limiting the process of profiling to,
for example, specific traces. For example, if a developer seeks to
profile only Java object allocations which refer to
java.lang.HashMap instances, then, using class filters 308, a
profiling allocation trace with a class filter applying exclusively
to java.lang.HashMap instances is started. Thread filters 304
relate to profiling annotations (e.g., specifying annotations),
such as when an allocation trace exists. Thread filters 304 may
also be used by the user to specify when and/or where a trace is to
be triggered and/or used. Buffer framework 306 is used to compress
and decompress any type of data or information that is being
communicated, stored, etc. Communication framework 312 is used to
facilitate communication of any data or information between and
within various components, elements, modules, systems, servers, VM,
etc. Communication framework 312 is also used to determine and
facilitate the storing of data or information, such as storing the
data using files or socket connections.
[0052] ID service 310 is employed to specify variables, such a
class, a name of the class, etc. to assign identification to them.
Once class, class names, etc. are assigned an ID (e.g., a number),
they are then mapped with each other and with various components
and variables via a mapping packet, instead of mapping by names.
Using ID service 310, the same can be done with threads and
methods. For example, by assigning IDs (instead of names) to
threads and methods, when dumping is performed, the IDs of threads
and methods are dumped rather than their names. This technique of
using IDs (e.g., numbers) instead of using the names is efficient,
fast, and saves memory.
[0053] For example, an allocation event is considered. ID numbers
are mapped to various packet names, such as java.Hashtable is
mapped to "2000", the thread (named, "main") is assigned "3", and
the user (named, "Hansi") is assigned "7". Stack trace is then
commenced using command lines, such as com.sap.test (line 30),
com.sap.submethod (line 2003), etc. The even information may then
be provided as 2000, 3, etc. It is known that ID number 2000 was
mapped to the underlying hashtable, while ID number 3 was mapped to
the thread. Using these ID's, names (e.g., main, Hansi, etc.) are
not needed and instead, IDs are used, which provides an easier
technique for packet name mapping. Similarly, object ID service 314
is used to assign IDs (e.g., numbers) to objects so the IDs can be
used to, for example, identify and compare the objects, instead of
using object names.
[0054] In one embodiment, profiling information and any other
relevant data is displayed at a display device via GUI at a client
so that a user can access and evaluate the displayed information.
The information may also be stored at a database and/or file system
for subsequent retrieval and analysis. Although Java components,
such as J2EE server, Java VM, Java heap, and Java memory errors,
etc., are discussed here for simplicity and brevity, it should be
noted, however, that the underlying principles and embodiments of
the present invention may be implemented within any type of
object-oriented and runtime environments. Moreover, it should be
noted that requirements and examples used in this document do not
necessarily reflect the real values that a system or program would
actually produce. For example, garbage collection may be invoked
multiple times while checking the VM heap memory size, so that
there are different VM implementations and, according to a relevant
VM specification, a given VM implementation might not clean up the
memory immediately after it has been requested to do so. Thus, to
be sure that a memory cleanup is provoked, the memory size may be
checked and the garbage collection may be invoked again, as
necessary.
[0055] Garbage collection as described here includes a process
designed to identify and reclaim blocks of memory that are
dispensed by a memory allocator but are no longer "alive" or "live"
(e.g., no longer being used, as determined, for example, by not
being reachable from any currently referenced objects or entities).
Garbage collection can sometimes be handled as a background task by
runtime systems rather than as an explicit task by user programs.
Garbage collection can also be handled as an inlined task. Garbage
collection can be used to reclaim memory in runtime systems, and
there are some well-known garbage collection algorithms (e.g.,
reference counting, mark-sweep, mark-compact, and copying
algorithms).
[0056] A VM (e.g., VM 206) is an example of a runtime system. A VM
refers to an abstract machine that includes an instruction set, a
set of registers, a stack, a heap, and a method area, such as a
machine or processor. A VM essentially acts as an interface between
program code and the actual processor or hardware platform on which
the program code is to be executed. The program code includes
instructions from the VM instruction set that manipulates the
resources of the VM. The VM executes instructions on the processor
or hardware platform on which the VM is running, and manipulates
the resources of that processor or hardware platform, so as to
effect the instructions of the program code. For example, a Java
source program can be compiled into program code, such as bytecode.
Bytecode can be executed on a VM, such as JVM, running on any
processor or platform. The JVM can either interpret the bytecode
one instruction at a time, or the bytecode can be further compiled
for the real processor or platform using a just-in-time (JIT)
compiler.
[0057] The illustrated VM 206 includes a JVM (e.g., SAP JVM), which
is used as an example; however, other examples of VMs, which can be
used in various embodiments, include Advanced Business Application
Programming (ABAP) language VMs, Common Language Runtime (CLR) VMs,
and the like. ABAP is a programming language for developing
applications for SAP systems, such as SAP R/3 system, which is a
widely installed business application system developed by SAP AG of
Walldorf, Germany. The CLR is a managed code execution environment
developed by Microsoft Corp. of Redmond, Wash. For simplicity and
brevity, the discussion in this document focuses on virtual
machines, and in particular Java virtual machine 104, but it is to
be understood that the techniques described herein can also be used
with other types of runtime systems.
[0058] A runtime system includes a code execution environment that
executes instructions or code in user requests and that provides
runtime services for that code. Code runtime services may include
functionality, such as process, thread, and memory management
(e.g., laying out objects in the server memory, sharing objects,
managing references to objects, and garbage collecting objects).
Enhanced runtime services may include functionality, such as error
handling and establishing security and connectivity.
[0059] The illustrated server 202 includes a J2EE
server/engine/node, which supports Enterprise Java Bean ("EJB")
components and EJB containers (at the business layer) and Servlets
and Java Server Pages ("JSP") (at the presentation layer). It is
understood that processes taught by the discussion above can be
practiced within various software environments such as, for
example, object-oriented and non-object-oriented programming
environments, Java based environments (such as a J2EE environment
or environments defined by other releases of the Java standard),
other environments (e.g., a .NET environment, a Windows/NT
environment each provided by Microsoft Corporation), and the
like.
[0060] FIG. 4 illustrates an embodiment of a process for profiling
using an embodiment of an on-demand profiling infrastructure. At
decision block 402, whether profiling need be started is
determined. If not, the non-profiling mode is maintained, which
saves system resources. If the profiling is to be started, the
profiling mechanism is switched to the profiling mode at processing
block 408. At decision block 410, a determination is made as to
whether online or offline profiling is to be performed. If the
profiling is to be performed online, the online profiling mode is
triggered for, for example, interactive profiling at processing
block 412.
[0061] Online profiling is started via Java APIs (e.g., server and
client Java APIs), using monitoring tools (e.g., Java VM monitor),
and/or using command lines. If the profiling is to be performed
offline, the offline profiling mode is triggered for, for example,
non-interactive profiling. Offline profiling can also be started
using monitoring tools, using command lines, and/or via Java APIs
as described above. At processing block 420, any profiling data
obtained from offline profiling is stored at an external source,
such as a profiling file. The data at the profiling file may be
stored in zipped format. At decision block 414, whether the process
of profiling be continued is determined. If yes, the profiling
continues with decision block 410. If not, the profiling status is
switched to the non-profiling mode at processing block 416. This
non-profiling mode is maintained at processing block 406.
[0062] FIG. 5 illustrates an embodiment of a mechanism 500 for
performing loitering trace at a virtual machine 206. Memory leaks
can occur for a number of reasons, such as, in many cases, memory
leaks can occur due to the failing of a clean-up operation at a
cache. For example, a cache is to be cleared at regular intervals,
and if a clean-up operation is to be interrupted even at the end of
the clean-up operation, some entries or objects may still exist and
not be detected. These entries or objects can cause a memory leak
if the cache were not able to remove such entries. Sometimes, even
a follow up clean-up operation may not clear the entries remaining
from the previous operation. In one embodiment, such objects or
entries that are not to be used anymore, but remain in the VM, and
can cause memory leaks and are detected using an embodiment of
loitering trace. A clean-up operation refers to a process being
performed at a VM 206 to remove the old and unused applications and
substitute them with new applications. The old or unused
applications may not be removed due to programming errors or
resource failures. It is contemplated that clean-up operation is
used here only as an example for brevity and that loitering trace
can be used for to cure and/or prevent any number of memory leak
causes.
[0063] In one embodiment, mechanism 500 includes a server 202
having a VM 206 (e.g., backend VM) that is the underlying VM and is
being profiled. VM 206 includes a profiling infrastructure having a
loitering trace module 318 and a hook 502. VM 206 is in
communication with another VM 214 (e.g., backend VM 214) that
resides at a client 216 in communication with the server 202. In
one embodiment, loitering trace module 318 is used to collect
information about unused objects at the VM 206 (e.g., objects in
the old generation) and generate statistics regarding the collected
information. Hook 502 is employed at the VM 206 to notify of the
profiling infrastructure 208 each time an object is used, which
includes whether (1) a method of this object is invoked; (2) a
field of this object is read to written; and (3) this object is
used for synchronization. If the loitering trace is enabled, the
object is marked as used. This information includes identifying (1)
objects that are being used and are alive, (2) objects that are not
being used but are alive; and (3) objects that are dead and are not
being used and are to be removed from the garbage collection
process. A report including such information is then generated
using the profiling infrastructure 208 to be sent to the requesting
VM 214 at client 216. It is contemplated that objects may not be
removed from the heap but rather, they are remembered and
reported.
[0064] It is contemplated that any references to Java-based
components, such as Java application server, Java VMs 206, 214,
Java objects, etc., are provided as examples and that the mechanism
500 and other embodiments of the present invention can also be used
with other non-Java-based environments and components. Furthermore,
a backend VM 206 may reside at the same J2EE engine as the tree
generation module or at another J2EE engine or at another server. A
server and a client may include servers and clients similar to
server 202 and client 216, respectively, of FIG. 2.
[0065] FIG. 6 illustrates an embodiment of a transaction sequence
for performing loitering trace. In one embodiment, loitering trace
request is initiated 602 via a client 602. Loitering trace is
initiated 604 via loitering trace module 318 at profiling
infrastructure 208. Further, at profiling infrastructure 208, using
hook, each time an object at a VM is used, whether the loitering
trace is enabled is checked 606. If the loitering trace is enabled,
the used object is marked in the heap. If the loitering trace is
not enabled, the process ends and nothing further occurs. Client
602 request stopping of the loitering trace 608. Loitering trace
stops 610. Further, the heap is iterated and any not used (not
marked) objects are found 612. The list of such objects is returned
614 to the client 602.
[0066] FIG. 7 illustrates an embodiment of a process for performing
loitering trace. A memory leak is detected at processing block 702.
Loitering trace is started at processing block 704. The loitering
trace is now running at processing block 706 and each time an
object is used, it is marked as used at processing block 708. When
the trace is stopped at processing block 710, a report of all
objects (including objects that are alive and being used, objects
alive and not being used, objects dead and not being used, etc.) is
formed at processing block 712. At processing block 714, the report
is communicated to one or more clients for one or more users to
access, use, and evaluate. In one embodiment, when the loitering
trace is enabled, it marks those objects that are used while it is
enabled. When the loitering trace is stopped, the objects that were
during the time the trace was active are now marked. Using this
technique, which objects were used and which objects were not used
are determined and a report stating that is formed and provided. To
provide these results, the loitering trace is to be running at some
time for a certain amount of time.
[0067] FIG. 8 illustrates an embodiment of a monitoring tool 220.
The illustrated monitoring tool 220 includes a JVM monitoring tool
(e.g., SAP JVM monitoring tool). Monitoring tool 220 includes a
menu line 802 that includes various menu items, such as command,
debugging, etc. Monitoring tool 220 further provides a list of VMs
804, and details about any VM 806 which includes a number of items,
such as performance, VM info, debugging, trace flags, local memory,
etc. Monitoring tool 220 further provides shared memory
configuration 808 and shared memory state 810. Monitoring tool 220
is illustrated merely as an example and the embodiment of the
present invention are in no way limited to using the illustrated
monitoring tool 220.
[0068] Processes taught by the discussion above may be performed
with program code, such as machine-executable instructions, which
can cause a machine (such as a "virtual machine", a general-purpose
processor disposed on a semiconductor chip, a special-purpose
processor disposed on a semiconductor chip, etc.) to perform
certain functions. Alternatively, these functions may be performed
by specific hardware components that contain hardwired logic for
performing the functions, or by any combination of programmed
computer components and custom hardware components.
[0069] One or more modules, components, or elements described
throughout this document, such as the ones shown within or
associated with the on-demand profiling infrastructure 206 of
profiling mechanism 200 of FIG. 2, may include hardware, software,
and/or a combination thereof. In a case where a module includes
software, the software data, instructions, and/or configuration may
be provided via an article of manufacture by a machine/electronic
device/hardware. An article of manufacture may include a machine
accessible/readable medium having content to provide instructions,
data, etc. The content may result in an electronic device, for
example, a filer, a disk, or a disk controller as described herein,
performing various operations or executions described. A machine
accessible medium includes any mechanism that provides (i.e.,
stores and/or transmits) information/content in a form accessible
by a machine (e.g., computing device, electronic device, electronic
system/subsystem, etc.). For example, a machine accessible medium
includes recordable/non-recordable media (e.g., read only memory
(ROM), random access memory (RAM), magnetic disk storage media,
optical storage media, flash memory devices, etc.), as well as
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waves, infrared signals, digital signals, etc.),
etc. The machine accessible medium may further include an
electronic device having code loaded on a storage that may be
executed when the electronic device is in operation. Thus,
delivering an electronic device with such code may be understood as
providing the article of manufacture with such content described
above. Furthermore, storing code on a database or other memory
location and offering the code for download over a communication
medium via a propagated signal may be understood as providing the
article of manufacture with such content described above. The code
may also be downloaded from a remote computer (e.g., a server) to a
requesting computer (e.g., a client) by way of data signals
embodied in a propagation medium (e.g., via a communication link
(e.g., a network connection)).
[0070] FIG. 9 illustrates an embodiment of a computing system 900.
Computing system 900 may be used for implementing one or more
embodiments of the present invention and for executing program code
stored by an article of manufacture. It is important to recognize
that the computing system 900 represents merely of various
computing system architectures that can be used for the same
purposes. The applicable article of manufacture may include one or
more fixed components (such as hard disk drive 902 or memory 906)
and/or various movable components, such as compact disk (CD) ROM
904, a compact disc, a magnetic tape, and the like. To execute the
program code, typically instructions of the program code are loaded
into RAM 906. Then, processing core 908 executes the instructions.
A processing core may include one or more processors and a memory
controller function. A virtual machine or "interpreter" (e.g., JVM)
may run on top of the processing core (architecturally speaking) to
convert abstract code (e.g., Java bytecode) into instructions that
are understandable to the specific processor(s) of processing core
908. Computing system 900 further includes network interface 910
and bus 912 to connect to other systems via a network and to have
various components communicate with each other, respectively.
[0071] FIG. 10 illustrates an embodiment of a client/server network
system 1000 employing an on-demand profiling infrastructure 1018.
As illustrated, network 1008 links server 1010 with client systems
1002-1006. Server 1010 includes programming data processing system
suitable for implementing apparatus, programs, and/or methods in
accordance with one or more embodiments of the present invention.
Server 1010 includes processor 1012 and memory 1014. Server 1010
provides a core operating environment for one or more runtime
systems (e.g., VM 1016) at memory 1014 to process user requests.
Memory 1014 may include a shared memory area that is accessible by
multiple operating system processes executing in server 1010. For
example, VM 1016 may include an enterprise server (e.g., a
J2EE-compatible server or node, Web Application Server developed by
SAP AG, WebSphere Application Server developed by IBM Corp. of
Armonk, N.Y., and the like). The enterprise server at VM 1016 may
host the on-demand profiling infrastructure 1018. Memory 1014 can
be used to store an operating system, a Transmission Control
Protocol/Internet Protocol (TCP/IP) stack for communicating over
network 1008, and machine executable instructions executed by
processor 1012. In some embodiments, server 1010 may include
multiple processors, each of which can be used to execute machine
executable instructions.
[0072] Client systems 1002-1006 may execute multiple application or
application interfaces. Each instance or application or application
interface may constitute a user session. Each user session may
generate one or more requests to be processed by server 1010. The
requests may include instructions or code to be executed on a
runtime system, such as VM 1016, on server 1010, such as the
requests made via the on-demand profiling infrastructure 1018 and
its components and modules as described throughout this
document.
[0073] In addition to what is described herein, various
modifications may be made to the disclosed embodiments and
implementations of the invention without departing from their
scope. Therefore, the illustrations and examples herein should be
construed in an illustrative, and not a restrictive sense. The
scope of the invention should be measured solely by reference to
the claims that follow.
* * * * *