Memory efficient classloading to reduce the number of class copies
A method is disclosed for reducing memory consumption in a run time environment by reducing copies of code in memory, wherein the method limits, based on the delegation, identical resources in memory and reduces memory consumption by not creating class loaders to load resources that are already loaded by existing class loaders.
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This application is a continuation of pending U.S. application Ser. No. 10/319,875 filed Dec. 13, 2002. This application additionally claims priority from U.S. Provisional Application No. 60/341,089, filed Dec. 13, 2001, which is hereby incorporated by reference in its entirety.
COMPUTER PROGRAM LISTINGApplicants submit herewith a software code on compact disc and in hard copy which is hereby incorporated by reference for each of its teachings and embodiments.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by any one of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF THE INVENTIONThis invention relates to the field of computer programming.
BACKGROUND OF THE INVENTIONObject-oriented programs, such as those written in Java, often incorporate classes or other resources that reside in existing libraries. The Java environment provides a means for loading such libraries on demand at runtime.
Runtime loading of library code in Java is achieved using software objects known as “classloaders.” Classloaders are adapted to obtain referenced library code, organize the code into classes (if necessary), and make the code available to software that references the library.
When library code is needed multiple times by a Java program, its classloader loads the library only once and caches it for future requests. A single Java runtime environment, however, often runs multiple applications at the same time, each of which is typically provided with its own classloader. Moreover, larger applications may instantiate multiple classloaders for different program components. When two applications or components require the same library code, their classloaders each load a copy of it into memory. This duplication requires additional memory and may significantly affect system performance.
A typical prior art scenario illustrating this problem is depicted in
As is further shown in
One possible approach for solving this problem might be to provide a single classloader for two or more applications. The shared classloader could examine the source code of both applications and identify all libraries referenced by both. It could then load a single copy of such common libraries for use by both applications.
This approach, however, suffers from several drawbacks. First, if the first and second applications require different versions of the same library, the classloader may load a version of the library not compatible with one of the applications.
Second, sharing a classloader in this way permits each application to load all classes and resources of the other application. Consequently, if one of the applications is malicious, it may harm the second application by, for example, creating instances, making invocations, or examining data of the second application.
SUMMARY OF THE INVENTIONThe present invention provides for a computer-based system for reducing memory consumption in a run time environment by reducing copies of code in memory, wherein the system comprises: a processor; and computer storage storing computer readable program code that is executable by the processor to reduce memory consumption in a run time environment by reducing copies of code in memory, and wherein the computer storage comprises computer readable program code for: (a) loading an application in the run time environment; (b) implementing a plurality of class loaders in memory, each class loader in the plurality of class loaders being associated with a resource; (c) implementing a store in memory comprising a plurality of references to existing class loaders stored in the memory, (d) implementing a first object adapted to identify at least one resource required by the application, the first object creating a second object adapted to retrieve the at least one resource, the second object determining if an existing class loader is available for loading the at least one resource, the second object determining if a reference exists to the existing class loader for the at least one resource, and the second object delegating task of loading the at least one resource to the existing class loader based on the determined reference; and (e) limiting, based on the delegation, identical resources in memory and reducing memory consumption by not creating class loaders to load resources that are already loaded by existing class loaders.
The present invention also provides a computer-based method for reducing memory consumption in a run time environment by reducing copies of code in memory, wherein the method comprises: (a) loading an application in the run time environment; (b) implementing a plurality of class loaders in memory, each class loader in the plurality of class loaders being associated with a resource; (c) implementing a store in memory comprising a plurality of references to existing class loaders stored in the memory, (d) implementing a first object adapted to identify at least one resource required by the application, the first object creating a second object adapted to retrieve the at least one resource, the second object determining if an existing class loader is available for loading the at least one resource, the second object determining if a reference exists to the existing class loader for the at least one resource, and the second object delegating task of loading the at least one resource to the existing class loader based on the determined reference; and (e) limiting, based on the delegation, identical resources in memory and reducing memory consumption by not creating class loaders to load resources that are already loaded by existing class loaders.
One preferred embodiment of the present invention is described in connection with an exemplary Java runtime environment such as the environment shown in
Each application 202-212 is preferably provided with a classloader 214. In a preferred embodiment, classloaders 214 are of a construction that differs from the construction of prior art classloaders, such as classloaders 114 in
As described in more detail below, a delegation classloader is adapted to identify libraries referenced in a piece of code and delegate the task of loading those libraries to a second object. The second object may be a delegation classloader or other loader, as described below. Illustratively, as shown in
In a preferred embodiment, each shared classloader 216 is preferably an “atomic” classloader, i.e., adapted to look at one library or a small set of libraries (e.g., one library and all libraries that it references). This makes it possible to reuse shared classloaders 216 since they provide only a relatively small set of resources and therefore do not expose application-specific resources to other applications.
Turning to
At 310, delegation classloader 300 identifies each library referenced by the application or other resource and adds the referenced libraries to a list. For example, in the illustrative scenario of
Delegation classloader 300 is preferably adapted to distinguish between resources that it will load itself and other resources with respect to which it will delegate that task. For example, a delegation classloader tasked with loading an application may itself load the application but delegate the task of loading any libraries referenced by the application. Alternatively, the programmer may specify the resources to be loaded directly by the delegation classloader and the resources for which the delegation classloader should delegate loading to another loader. In the illustrative scenario of
At 312, the delegation classloader determines whether an existing loader is available to load each library in the list. In a preferred embodiment, this determination is made by consulting a store of existing loaders. One preferred embodiment for implementing such a store is shown in
As shown in
In an alternative preferred embodiment, the delegation classloader may directly determine whether or not an instance of each library in the list (or any required resource generally) is available in memory. In a preferred embodiment, this determination may be made by consulting a store that includes available libraries (and resources) or references to such libraries (and resources). More generally, the determination may be made by communicating directly or indirectly with other loaders or system entities to locate and use an available instance of a required library (or resource) in memory.
Returning to
By contrast, for each resource in the list without an existing delegation classloader, delegation classloader 300 returns to step 302 to initiate creation of an appropriate classloader to load the library. For example, in the illustrative scenario of
To maximize efficient sharing of libraries, the classloaders created in this step preferably load only a single library. In some preferred embodiments, however, the system may be configured to allocate loading of some set of libraries to a single classloader. This may be advantageous where, for example, one library includes references to several others or where some small set of libraries are otherwise related.
In a preferred embodiment, the present system and method may comprise a number of different delegation classloaders each adapted to load a different library format. Each library preferably comprises a collection of resources which may, for example, comprise one or more classes, Web pages, or other resources that may be served by a classloader. Suitable delegation classloaders may be provided for Java archives, Web archives, or any other desired format. Delegation classloader 300 preferably identifies the format of the required library and creates a suitable delegation classloader (or other loader) for loading that format.
A reference to the new delegation classloader for the referenced resource is preferably added to store 400 (in embodiments that comprise such a store). Consequently, the next time a delegation classloader consults the store, the reference will be found, thus avoiding the need to load a second copy of the library.
As demonstrated by
In some cases, two or more libraries required by a program may include circular references to each other. In such cases, the recursive nature of the model shown in
Shown in
As noted above, delegation classloaders are preferably provided for any required library formats. In one preferred implementation of the present system and method which simplifies classloader construction, format-specific aspects of the classloader function are allocated to an abstraction layer that comprises objects referred to herein as bytes providers. The resulting simplified delegation classloaders are referred to herein as bytes provider delegation classloaders or BP delegation classloaders.
As above, BP delegation classloader 602 preferably delegates the task of loading libraries referenced in the application or other resource for which it is directly responsible to a distinct software object, such as another BP delegation classloader 606. In a preferred embodiment, each BP delegation classloader 606 is an atomic classloader responsible for a single library or small set of libraries. Each BP delegation classloader 606 is also preferably paired with an associated bytes provider adapted to look at the library or small set of libraries and provide bytes from the library or libraries to BP delegation classloader 606.
A preferred embodiment of a bytes provider hierarchy is shown in
Hierarchy 700 further preferably comprises an abstract bytes provider 708 which extends interface 702. Abstract bytes provider 708 preferably defines a plurality of methods for reading data out of a bytes provider. In a preferred embodiment, these include a getResourceAsBytes method 710, a getResourceAsStream method 712, and a getResourceURL method 714.
Hierarchy 700 further preferably comprises a plurality of specific bytes providers 716-720. These include a URLBytesProvider 716 that looks at a URL, a DiskCacheJarBytesProvider 718, and a MemoryCacheJarBytesProvider 720. Bytes providers 718 and 720 preferably look at JAR files, and are adapted to cache a JAR by loading it into memory or expanding it on disk, respectively. In a preferred embodiment, the decision whether to cache a JAR in memory or on disk is preferably based on an evaluation of the cache watermark settings and available memory.
In a preferred embodiment, additional bytes providers suitable for reading any desired format may be provided. These may be necessary, for example, in cases where a loading mechanism is required that is not provided by any of the bytes providers shown in
Also shown in
GroupedWrapperBytesProvider 728 is preferably adapted to wrap around an arbitrary set of bytes providers and provide a single interface to all libraries looked at by those bytes providers. This may be useful, for example, if the bytes providers serve as one logical unit or they are associated with a single classloader. In addition, by creating a GroupedWrapperBytesProvider 728 around all bytes providers, it is possible to effectively disable delegation classloading and provide a single interface for loading any library.
In operation, when a BP delegation classloader wishes to delegate the task of loading a resource to another classloader, it determines whether a bytes provider or other loader for the resource exists. As above, this step may be achieved by consulting a store or by alternative means.
If an existing bytes provider for the resource is found, the calling BP delegation classloader invokes the bytes provider's getClassLoader method to obtain the bytes provider's BP delegation classloader. It then delegates the task of providing the resource to the BP delegation classloader. Alternatively, if another loader for the resource is found, the BP delegation classloader delegates the task of loading the resource to the loader.
One preferred embodiment for a store 800 is shown in
It should be noted that, although the concept of wrapper objects for multiple libraries has been described in connection with the bytes provider implementation, analogous wrappers may be provided in alternative implementations that do not employ bytes providers. Thus, as shown in
It should also be noted that although the above embodiments have been described primarily in terms of a Java runtime environment, those skilled in the art will recognize that the principles of the present invention are capable of application in other runtime environments such as Microsoft's .Net runtime environment. For example, as understood in the art, .Net uses the term assembly resolver to describe a software component that is functionally analogous to a classloader in Java. For purposes of the present application, applicant intends that terms such as classloader, class, loading, and library be understood in their functional sense, and be construed to cover their respective analogs in other runtime environments.
While the invention has been described in conjunction with specific embodiments, it is evident that numerous alternatives, modifications, and variations will be apparent to those persons skilled in the art in light of the foregoing description.
Claims
1-29. (canceled)
30. A computer-based system for reducing memory consumption in a run time environment by reducing copies of code in memory, comprising:
- a processor; and
- computer storage storing computer readable program code that is executable by said processor to reduce memory consumption in a run time environment by reducing copies of code in memory, said computer storage comprising:
- computer readable program code loading an application in said run time environment;
- computer readable program code implementing a plurality of class loaders in memory, each class loader in said plurality of class loaders being associated with a resource;
- computer readable program code implementing a store in memory comprising a plurality of references to existing class loaders stored in the memory,
- computer readable program code implementing a first object adapted to identify at least one resource required by said application, said first object creating a second object adapted to retrieve said at least one resource, said second object determining if an existing class loader is available for loading said at least one resource, said second object determining if a reference exists to said existing class loader for said at least one resource, and said second object delegating task of loading said at least one resource to said existing class loader based on said determined reference; and
- computer readable program code limiting, based on said delegation, identical resources in memory and reducing memory consumption by not creating class loaders to load resources that are already loaded by existing class loaders.
31. The computer-based system of claim 30, wherein said first object is a delegation class loader.
32. The computer-based system of claim 30, wherein said second object is a delegation class loader.
33. The computer-based system of claim 30, wherein said at least one resource is a single library.
34. The computer-based system of claim 30, wherein said at least one resource is a single library and its direct dependencies.
35. The computer-based system of claim 30, wherein said at least one resource is a single library and its related libraries.
36. The computer-based system of claim 30, wherein said at least one resource includes one or more classes.
37. The computer-based system of claim 30, wherein said at least one resource includes one or more web pages.
38. The computer-based system of claim 30, wherein said at least one resource is a.Net assembly.
39. The computer-based system of claim 30, wherein said run time environment is a virtual machine environment.
40. A computer-based method for reducing memory consumption in a run time environment by reducing copies of code in memory, steps of said method executed on a computer, said method comprising:
- loading an application in said run time environment;
- implementing a plurality of class loaders in memory, each class loader in said plurality of class loaders being associated with a resource;
- implementing a store in memory comprising a plurality of references to existing class loaders stored in the memory,
- implementing a first object adapted to identify at least one resource required by said application, said first object creating a second object adapted to retrieve said at least one resource, said second object determining if an existing class loader is available for loading said at least one resource, said second object determining if a reference exists to said existing class loader for said at least one resource, and said second object delegating task of loading said at least one resource to said existing class loader based on said determined reference; and
- limiting, based on said delegation, identical resources in memory and reducing memory consumption by not creating class loaders to load resources that are already loaded by existing class loaders.
41. The computer-based method of claim 40, wherein said first object is a delegation class loader.
42. The computer-based method of claim 40, wherein said second object is a delegation class loader.
43. The computer-based method of claim 40, wherein said at least one resource is a single library.
44. The computer-based method of claim 40, wherein said at least one resource is a single library and its direct dependencies.
45. The computer-based method of claim 40, wherein said at least one resource is a single library and its related libraries.
46. The computer-based method of claim 40, wherein said at least one resource includes one or more classes.
47. The computer-based method of claim 40, wherein said at least one resource includes one or more web pages.
48. The computer-based method of claim 40, wherein said at least one resource is a.Net assembly.
49. The computer-based method of claim 40, wherein said run time environment is a virtual machine environment.
Type: Application
Filed: Jan 28, 2010
Publication Date: Aug 12, 2010
Applicant: IONA TECHNOLOGIES LIMITED (Hamilton)
Inventors: Allaert J.D. Bosschaert (Wijster), Philip J. Murphy (Dublin), David J. Hayes (Dublin), Sean P. Baker (Co.Wicklow)
Application Number: 12/656,380
International Classification: G06F 9/44 (20060101);