WO2003042845A1 - Javascript engine - Google Patents

Javascript engine Download PDF

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Publication number
WO2003042845A1
WO2003042845A1 PCT/US2002/035831 US0235831W WO03042845A1 WO 2003042845 A1 WO2003042845 A1 WO 2003042845A1 US 0235831 W US0235831 W US 0235831W WO 03042845 A1 WO03042845 A1 WO 03042845A1
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Prior art keywords
request
context
thread
scope
javascript engine
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PCT/US2002/035831
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French (fr)
Inventor
Brendan Eich
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America Online Incorporated
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Publication of WO2003042845A1 publication Critical patent/WO2003042845A1/en

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F9/00—Arrangements for program control, e.g. control units
    • G06F9/06—Arrangements for program control, e.g. control units using stored programs, i.e. using an internal store of processing equipment to receive or retain programs
    • G06F9/46—Multiprogramming arrangements
    • G06F9/52—Program synchronisation; Mutual exclusion, e.g. by means of semaphores
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S707/00—Data processing: database and file management or data structures
    • Y10S707/99931—Database or file accessing
    • Y10S707/99938—Concurrency, e.g. lock management in shared database
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S707/00—Data processing: database and file management or data structures
    • Y10S707/99941—Database schema or data structure
    • Y10S707/99943—Generating database or data structure, e.g. via user interface

Definitions

  • the invention relates to locking mechanisms. More particularly, the invention relates to a JavaScript enhancement that increases the performance of the JavaScript by avoiding the use of locking mechanisms in multi-threaded sessions.
  • Multi-threaded technology is well known and well used in the computer programming and application development industry.
  • multi-threaded programming is permitted and supported by the World Wide Web (Web) and particularly within the JavaScript language.
  • Web browsers and Web servers communicate with each other using multi-threaded technology to deliver information, whether in graphical format or in other media, to end users.
  • multi-threaded situation where more than one task is performed simultaneously, it is possible for more than one thread to try to access a same encapsulated programming object, thus creating problems if that object's state is being changed by one of the sharing threads.
  • Locking mechanisms are known in the art to lock an object by a thread requesting access to that object, thereby preventing it from being accessed by another thread until the first thread is done with the object.
  • locking mechanisms can be expensive because they add overhead before and after the critical code sections that acquire and release the lock, and because in the case of contention for a lock among multiple threads, they incur further overhead.
  • Barlow et al Systems and Methods for Locking Interactive Objects having one or more object states.
  • An object designer interactively assigns one or more object behaviors to each object state.
  • An end user of the object displays the object behavior associated with an object state, typically by invoking the object state with an input device.
  • a lock behavior provides a way of locking an object behavior or aspect of an object.
  • the object designer sets which aspects of an object are to be locked, and a lock controller prevents active access to those aspects accordingly.
  • an object can be locked based on a password or based on the location of display of the object.
  • Barlow et al do not teach locking an object under an atypical situation where an object is not owned exclusively by the current thread in a JavaScript engine.
  • U.S. Patent No. 6,292,936 discloses an interpreter- based embedded scripting environment that includes multiple runtime processors executed by a computer. Each of the runtime processors processes their respective corresponding intermediate sources derived from an original input source in a synchronous manner. One or more of the respective corresponding intermediate sources includes a synchronizer token that provides synchronization among the runtime processors. Using the synchronizer token, an execution sequence of the original input source is maintained. Nowhere does Wang teach or even suggest locking an object under an atypical situation where an object is not owned exclusively by the current thread in a JavaScript engine.
  • Braband et al disclose that they deal with all of these scenarios in a uniform manner based on a central controller process in a runtime system. However, nowhere do Braband et al teach or even suggest providing a simple and elegant enhancement that avoids use of locking mechanisms that otherwise create a lot of overhead.
  • a JavaScript enhancement is provided that increases performance of the JavaScript by avoiding the use of locking mechanisms in multi-threaded sessions. To do so, an object is deemed owned by a thread exclusively until the script is ended or suspended. Because scripts are typically short and complete quickly, the overhead to start and end a request containing a script is much less than the overhead of locking each and every object access done by the script, on average.
  • Fig. 1 shows an HTML engine transmitting JavaScript source code, such as from an HTML page, to a JavaScript engine according to the prior art
  • Fig. 2 shows the data structure of an object, o, having a scope component and a slots component according to the prior art
  • Fig. 3 depicts an object, o, of interest to two different threads, , and T 2 , according to the prior art
  • Fig. 4 is a schematic diagram showing the control flow of a plurality of threads with the JavaScript engine, and the control flow of a garbage collector thread with the garbage collector component of the JavaScript engine according to the prior art;
  • Fig. 5 is a graph showing that a garbage collector waits to start collecting garbage until all outstanding requests have been completed according to the prior art
  • Fig. 6 is a schematic diagram of object o of Fig. 2 also showing an additional attribute of object o, the owner, cx ⁇ that corresponds to thread T 1 having a context of c ⁇ .,according to the prior art;
  • Fig. 7 is a graph showing threads ⁇ and T 2 having contexts of ex., and cx 2 , respectively, each making requests R ⁇ and R 2 , respectively, to the JavaScript engine to use object o simultaneously according to the invention.
  • Fig. 8 is a graph showing threads T ⁇ and T 2 having contexts of cx 1 and cx 2 , respectively, each making successful requests R ⁇ and R 2 , respectively, to the JavaScript engine to use object o according to the invention.
  • a JavaScript enhancement is provided that increases performance of the JavaScript by avoiding the use of locking mechanisms in multi-threaded sessions. To do so, an object is deemed owned by a thread exclusively until the script is ended or suspended. Because scripts are typically short and complete quickly, the overhead to start and end a request containing a script is much less than the overhead of locking each and every object access done by the script, on average. In fact, both overheads added together are still less than the sum of all object lock/unlock overhead for a script that accesses object properties many times, as most scripts, even short ones, do.
  • a Web browser requests a Web page, such as, for example, page.html, and such page may contain JavaScript source such as depicted in Table A, wherein Table A is an example of JavaScript source code.
  • Fig. 1 shows that an HTML engine 101 transmits JavaScript source code, such as in Table A from an HTML page to a JavaScript engine 102 according to the prior art.
  • the JavaScript engine at times interprets data assignments to JavaScript objects.
  • a variable, or object, "o" is assigned a value of "42" to its property "p", as in the first line of Table B.
  • the second line of Table B shows that the p property of o, i.e. o.p, is assigned to a different value, namely 43.
  • Table B shows in line three that a second property "q" is defined for o, i.e. o.q, and is assigned the value 44.
  • Fig. 2 shows the data structure of the object, o 201 having a scope component 202 and a slots component 203.
  • the scope component 202 has entries for each of o's properties. For example, the first scope entry 202a has "p" assigned to a name attribute, and 3 assigned to a slot attribute. The second scope entry has "q" assigned to the name attribute and 4 assigned to the slot attribute.
  • the fourth entry 203a, slot 3 had an assigned value of 42 updated to a new assigned value of 43.
  • the fifth entry 203b, slot 4 is assigned the value of 44.
  • FIG. 3 depicts the same object of interest to two different threads, X, 301 and T 2 302. It is clear to discern from Fig. 3 that whether slot 3 203a has the value of 42 or 43 depends on the timing of accessing slot 3 203a.
  • the JavaScript engine has a garbage collector mechanism that together with particular JavaScript engine application program interface (API) commands, based on a JavaScript request model, perform a type of object locking control.
  • the JavaScript request model is described with reference to Fig. 4, a schematic diagram showing typical control flow 401 of a thread T, 301 with the JavaScript engine 102, and the control flow 402 of a garbage collector thread 403 with the garbage collector component 404 of the JavaScript engine 102.
  • the JavaScript engine 102 responds to requests from threads by recognizing and interpreting begin request and end request commands as illustrated in Table C below.
  • the garbage collector component 404 When the garbage collector component 404 begins to collect garbage, it checks whether or not any begin request commands are outstanding. If so, the garbage collector component 404 waits until such outstanding begin request commands are terminated by their respective end request command.
  • the request model is described with reference to Fig. 5, a graph showing a garbage collector waiting to start collecting garbage until after all outstanding requests are completed. Also, any begin request made while the garbage collection in progress is suspended until garbage collection has completed. The such request can resume. A plurality of relatively short requests are plotted against time. Those requests ending before the garbage collector begins 501a at time t, do not impact when the garbage collector starts at time t 2 . Those requests in progress 501 b when the garbage collector tries to begin at time ⁇ affect when the garbage collector actually beings. The garbage collector waits until the last request is finished which is at time t 2 . At time t 3 another request is made 501c, but is not allowed to proceed until the garbage collector is finished which is time t 4 . At time t 4 such request is allowed to proceed. Any other request 501 d made after time t 4 is allowed to proceed normally. Thus, the garbage collector 406 respects the begin request commands by waiting until they are finished.
  • an object can be explicitly locked until it is no longer used.
  • the JS_LOCK_OBJ command taking two arguments, one of them being the context, i.e. the thread, and the other being the object, can be used to lock the object.
  • An example of using JS_LOCK_OBJ is shown in Table D of pseudocode for adding element o.q (202b and 203b) to object o of Fig. 2 by first locking object o.
  • the procedure for locking object o to avoid simultaneously accessing an object described herein above and illustrated in Table D is expensive, because it, for one reason, causes the runtime to take too long from the perspective of an end user.
  • the preferred embodiment of the invention provides a way of avoiding using a locking mechanism when it is not needed.
  • the JavaScript engine is instructed first to check if the owner of the object's scope, i.e. context, is the same entity as that used by the current thread. If they are the same, then there is no need to request locking the object. If they are not the same, then the JavaScript engine is instructed to promote a lock on the object's scope. Table E below provides an example of such pseudocode.
  • the owner of an object is set in, but is not limited to, the following three situations:
  • Fig. 7 is a graph showing a thread T., having a context of cx and making a request R ⁇ to the JavaScript engine at time ⁇ that uses object o.
  • a second thread T 2 having a context cx 2 begins a request R 2 to the JavaScript engine at a time t 2 .
  • R 2 requests to use object o.
  • the JavaScript engine compares the context of thread T 2 , cx 2 , with the ownership of object o, cx 1 ( and discovers that they are different.
  • the JavaScript engine suspends R 2 at time t 3 until R., has completed using object o, which is at time t 4 .
  • the JavaScript engine sets the ownership of object o to 'null' and resumes R 2 .
  • FIG. 8 is a graph showing a thread T, having a context of c making a request R to the JavaScript engine at time t, that uses object o. Thread T, is done with request R., at time t 2 . A little further in time, a second thread T 2 having a context cx 2 begins a request R 2 to the JavaScript engine at a time t 3 which is after time t 2 . R 2 requests to use object o. The JavaScript engine sets the ownership of object o to cx 2 , because T 2 is allowed to claim exclusive ownership to object o.
  • R 2 completes at time t 4 with no suspensions on account of object o being used simultaneously by another thread.

Abstract

A JavaScript enhancement is provided that increases performance of the javaScript by avoiding the use of locking mechanisms in multi-threaded sessions. To do so, an object is deemed owned by a thread exclusively until the script is ended or suspended. Because scripts are typically short and complete quickly, the overhead to start and end a request containing a script is much less than the overhead of locking each and every object access done by the script, on average.

Description

JavaScript Engine
BACKGROUND OF THE INVENTION
TECHNICAL FIELD
The invention relates to locking mechanisms. More particularly, the invention relates to a JavaScript enhancement that increases the performance of the JavaScript by avoiding the use of locking mechanisms in multi-threaded sessions.
DESCRIPTION OF THE PRIOR ART
Multi-threaded technology is well known and well used in the computer programming and application development industry. In particular, multi-threaded programming is permitted and supported by the World Wide Web (Web) and particularly within the JavaScript language. Web browsers and Web servers communicate with each other using multi-threaded technology to deliver information, whether in graphical format or in other media, to end users. In a multi-threaded situation, where more than one task is performed simultaneously, it is possible for more than one thread to try to access a same encapsulated programming object, thus creating problems if that object's state is being changed by one of the sharing threads.
Locking mechanisms are known in the art to lock an object by a thread requesting access to that object, thereby preventing it from being accessed by another thread until the first thread is done with the object. However, locking mechanisms can be expensive because they add overhead before and after the critical code sections that acquire and release the lock, and because in the case of contention for a lock among multiple threads, they incur further overhead.
S. Barlow, E. Leaphart, Jr., G. V. Strazds, and C. Rudbart (herein referred to as Barlow et al), Systems and Methods for Locking Interactive Objects, U.S. Patent No. 6,275,935 (Aug. 14, 2001) disclose an object locking system for preventing unauthorized modification of interactive objects having one or more object states. An object designer interactively assigns one or more object behaviors to each object state. An end user of the object displays the object behavior associated with an object state, typically by invoking the object state with an input device. A lock behavior provides a way of locking an object behavior or aspect of an object. The object designer sets which aspects of an object are to be locked, and a lock controller prevents active access to those aspects accordingly. In addition, an object can be locked based on a password or based on the location of display of the object. Barlow et al do not teach locking an object under an atypical situation where an object is not owned exclusively by the current thread in a JavaScript engine.
A. I. Wang, Enabling Multiple Runtime Processors in an Interpreter-Based Embedded Scripting System, U.S. Patent No. 6,292,936 discloses an interpreter- based embedded scripting environment that includes multiple runtime processors executed by a computer. Each of the runtime processors processes their respective corresponding intermediate sources derived from an original input source in a synchronous manner. One or more of the respective corresponding intermediate sources includes a synchronizer token that provides synchronization among the runtime processors. Using the synchronizer token, an execution sequence of the original input source is maintained. Nowhere does Wang teach or even suggest locking an object under an atypical situation where an object is not owned exclusively by the current thread in a JavaScript engine.
C. Braband, A. Moller, and M. I. Schwartzbach, The <Big Wig> Project. BRICS, Department of Computer Science, University of Aarhus, Denmark {brabrand,amoeller,mis}@brics.dk disclose the results of a project that aimed to design and implement a high-level domain-specific language for programming interactive Web services. They disclose that a mechanism is needed to discipline the concurrent behavior of the active threads. They continue to say that a simple case is to control access to the shared variables, using mutex regions or the readers/writers protocol. Another issue, they put forth, is enforcement of priorities between different session kinds, such that a management session may block other sessions from starting; a final example being event handling, where a session thread may wait for certain events to be caused by other threads. Braband et al disclose that they deal with all of these scenarios in a uniform manner based on a central controller process in a runtime system. However, nowhere do Braband et al teach or even suggest providing a simple and elegant enhancement that avoids use of locking mechanisms that otherwise create a lot of overhead.
It would be advantageous to increase performance of a JavaScript engine by avoiding the unnecessary use of locking mechanisms in multi-threaded sessions.
SUMMARY OF THE INVENTION A JavaScript enhancement is provided that increases performance of the JavaScript by avoiding the use of locking mechanisms in multi-threaded sessions. To do so, an object is deemed owned by a thread exclusively until the script is ended or suspended. Because scripts are typically short and complete quickly, the overhead to start and end a request containing a script is much less than the overhead of locking each and every object access done by the script, on average.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows an HTML engine transmitting JavaScript source code, such as from an HTML page, to a JavaScript engine according to the prior art;
Fig. 2 shows the data structure of an object, o, having a scope component and a slots component according to the prior art;
Fig. 3 depicts an object, o, of interest to two different threads, , and T2, according to the prior art;
Fig. 4 is a schematic diagram showing the control flow of a plurality of threads with the JavaScript engine, and the control flow of a garbage collector thread with the garbage collector component of the JavaScript engine according to the prior art;
Fig. 5 is a graph showing that a garbage collector waits to start collecting garbage until all outstanding requests have been completed according to the prior art; Fig. 6 is a schematic diagram of object o of Fig. 2 also showing an additional attribute of object o, the owner, cx^ that corresponds to thread T1 having a context of cχ.,according to the prior art;
Fig. 7 is a graph showing threads ^ and T2 having contexts of ex., and cx2, respectively, each making requests Rλ and R2, respectively, to the JavaScript engine to use object o simultaneously according to the invention; and
Fig. 8 is a graph showing threads T^ and T2 having contexts of cx1 and cx2, respectively, each making successful requests R^ and R2, respectively, to the JavaScript engine to use object o according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
A JavaScript enhancement is provided that increases performance of the JavaScript by avoiding the use of locking mechanisms in multi-threaded sessions. To do so, an object is deemed owned by a thread exclusively until the script is ended or suspended. Because scripts are typically short and complete quickly, the overhead to start and end a request containing a script is much less than the overhead of locking each and every object access done by the script, on average. In fact, both overheads added together are still less than the sum of all object lock/unlock overhead for a script that accesses object properties many times, as most scripts, even short ones, do.
For a better understanding of the invention, an overview of part of Web browser/server basic communication is described with reference to Table A and Figs. 1-3 below. A Web browser requests a Web page, such as, for example, page.html, and such page may contain JavaScript source such as depicted in Table A, wherein Table A is an example of JavaScript source code.
Table A <script> alert ("hi"); </script>
Fig. 1 shows that an HTML engine 101 transmits JavaScript source code, such as in Table A from an HTML page to a JavaScript engine 102 according to the prior art.
Additionally, the JavaScript engine at times interprets data assignments to JavaScript objects. For example, in Table B herein below, a variable, or object, "o" is assigned a value of "42" to its property "p", as in the first line of Table B. The second line of Table B shows that the p property of o, i.e. o.p, is assigned to a different value, namely 43. Finally, Table B shows in line three that a second property "q" is defined for o, i.e. o.q, and is assigned the value 44.
Table B var o = {p:42}; o.p = 43; O.q = 44;
Fig. 2 shows the data structure of the object, o 201 having a scope component 202 and a slots component 203. The scope component 202 has entries for each of o's properties. For example, the first scope entry 202a has "p" assigned to a name attribute, and 3 assigned to a slot attribute. The second scope entry has "q" assigned to the name attribute and 4 assigned to the slot attribute. Similarly, in the slots component 203, the fourth entry 203a, slot 3, had an assigned value of 42 updated to a new assigned value of 43. The fifth entry 203b, slot 4, is assigned the value of 44.
Thus, by reference to Fig. 2, it is easy to see that if two threads request modifying the same object, confusion or error result. Fig. 3 depicts the same object of interest to two different threads, X, 301 and T2 302. It is clear to discern from Fig. 3 that whether slot 3 203a has the value of 42 or 43 depends on the timing of accessing slot 3 203a.
To avoid the potential confusion rendered by two or more threads accessing an object simultaneously, interlocking mechanisms have been created and implemented. For example, in JavaScript, per-scope locks are available and used for the following situations: • when adding a property;
• when deleting a property;
• when looking up a property; and
• when getting a property value.
It should be appreciated that such objects discussed above are rarely shared among threads. That is, it is rare that two or more threads will request action on the same object simultaneously or in any temporal overlapping fashion.
It should also be appreciated that the JavaScript engine has a garbage collector mechanism that together with particular JavaScript engine application program interface (API) commands, based on a JavaScript request model, perform a type of object locking control. The JavaScript request model is described with reference to Fig. 4, a schematic diagram showing typical control flow 401 of a thread T, 301 with the JavaScript engine 102, and the control flow 402 of a garbage collector thread 403 with the garbage collector component 404 of the JavaScript engine 102. Specifically, the JavaScript engine 102 responds to requests from threads by recognizing and interpreting begin request and end request commands as illustrated in Table C below.
Table C JS_BeginRequest
JS_EvaluateScript(..."alert( 'hi' )") ;
JS_ErιdRequest
When the garbage collector component 404 begins to collect garbage, it checks whether or not any begin request commands are outstanding. If so, the garbage collector component 404 waits until such outstanding begin request commands are terminated by their respective end request command.
The request model is described with reference to Fig. 5, a graph showing a garbage collector waiting to start collecting garbage until after all outstanding requests are completed. Also, any begin request made while the garbage collection in progress is suspended until garbage collection has completed. The such request can resume. A plurality of relatively short requests are plotted against time. Those requests ending before the garbage collector begins 501a at time t, do not impact when the garbage collector starts at time t2. Those requests in progress 501 b when the garbage collector tries to begin at time ^ affect when the garbage collector actually beings. The garbage collector waits until the last request is finished which is at time t2. At time t3 another request is made 501c, but is not allowed to proceed until the garbage collector is finished which is time t4. At time t4 such request is allowed to proceed. Any other request 501 d made after time t4 is allowed to proceed normally. Thus, the garbage collector 406 respects the begin request commands by waiting until they are finished.
Similarly, an object can be explicitly locked until it is no longer used. In the JavaScript language, for example, the JS_LOCK_OBJ command taking two arguments, one of them being the context, i.e. the thread, and the other being the object, can be used to lock the object. An example of using JS_LOCK_OBJ is shown in Table D of pseudocode for adding element o.q (202b and 203b) to object o of Fig. 2 by first locking object o.
Table D
JSJ OCK_OBJ(context,object) lookup "q" if "q" not found add "q" store 44 in slot 3 JS_UNLOCK_OBJ(context,object)
It should be appreciated that the procedure for locking object o to avoid simultaneously accessing an object described herein above and illustrated in Table D is expensive, because it, for one reason, causes the runtime to take too long from the perspective of an end user. The preferred embodiment of the invention provides a way of avoiding using a locking mechanism when it is not needed. According to the preferred embodiment of the invention, the JavaScript engine is instructed first to check if the owner of the object's scope, i.e. context, is the same entity as that used by the current thread. If they are the same, then there is no need to request locking the object. If they are not the same, then the JavaScript engine is instructed to promote a lock on the object's scope. Table E below provides an example of such pseudocode.
Table E if (object' s scope is owned by 'context') do nothing; else { promote object's scope lock;
(that is, something expensive at the OS-level locking) }
In the preferred embodiment of the invention, the owner of an object is set in, but is not limited to, the following three situations:
• when the scope is initially created , then set the scope's ownership to the current thread's context;
• when a second thread claims exclusive ownership of a scope, after the first thread is done with it, set the ownership to the second thread's context; and
• when ownership is shared, i.e. when a second thread requests using the object and the first thread is not presently finished with the object, then set the object's ownership to null.
It should be appreciated that in the last situation, setting the ownership to null for shared ownership is an expensive process. For further understanding of the preferred embodiment of the invention, an additional attribute of object o, the owner of the object, ex., 601 that corresponds to thread T1 having a context of cx 601 , is shown in Fig. 6.
An implementation of the locking mechanism according to the preferred embodiment of the invention is described with reference to Fig. 7. Fig. 7 is a graph showing a thread T., having a context of cx and making a request R^ to the JavaScript engine at time ^ that uses object o. A little further in time, a second thread T2 having a context cx2 begins a request R2 to the JavaScript engine at a time t2. At time t3, R2 requests to use object o. The JavaScript engine compares the context of thread T2, cx2, with the ownership of object o, cx1 ( and discovers that they are different. The JavaScript engine suspends R2 at time t3 until R., has completed using object o, which is at time t4. At time t4, the JavaScript engine sets the ownership of object o to 'null' and resumes R2.
An example of successful claims on object o defined as when no locking mechanism is used, according to the invention is described with reference to Fig. 8. Fig. 8 is a graph showing a thread T, having a context of c making a request R to the JavaScript engine at time t, that uses object o. Thread T, is done with request R., at time t2. A little further in time, a second thread T2 having a context cx2 begins a request R2 to the JavaScript engine at a time t3 which is after time t2. R2 requests to use object o. The JavaScript engine sets the ownership of object o to cx2, because T2 is allowed to claim exclusive ownership to object o. R2 completes at time t4with no suspensions on account of object o being used simultaneously by another thread. Although the invention is described herein with reference to the preferred embodiment, one skilled in the art will readily appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention should only be limited by the Claims included below.

Claims

1. A method for avoiding using a locking mechanism when a thread having a context requests to use an object having a scope and having an owner of said scope, said method comprising: determining if said owner is the same as said context; if said owner is the same as said context, then avoiding using locking mechanism; if said owner is not the same as said context, then promoting a lock on said object's scope.
2. The method of Claim 1 , further comprising: initially setting said object's scope's owner to a current context of a current thread when said object's scope is created; resetting said object's scope's owner to a second thread's context when said second thread claims exclusive ownership of said scope; and setting said object's scope's owner to null when said ownership is shared.
3. A method for locking an object having an ownership attribute, wherein a first thread having a first context makes a first request to a JavaScript engine at a first time, said first request comprising using said object, and a second thread having a second context makes a second request to the JavaScript engine at a second and later time, said second request comprising using said object, said method comprising: said JavaScript engine determining if said first request is finished with said object; if said first request is not finished with said object, then: said JavaScript engine comparing said second context of said second thread with said ownership attribute of said object; if said comparison is different, then suspending said second request until said first request is finished with said object; said JavaScript engine setting said ownership attribute of said object to null; said JavaScript engine resuming said second request; otherwise, said JavaScript engine setting said ownership attribute of said object to said second context and processing said second request.
4. An apparatus for avoiding using a locking mechanism when a thread having a context requests to use an object having a scope and having an owner of said scope, said apparatus comprising: means for determining if said owner is the same as said context; if said owner is the same as said context, then means for avoiding using locking mechanism; if said owner is not the same as said context, then means for promoting a lock on said object's scope.
5. The apparatus of Claim 4, further comprising: means for initially setting said object's scope's owner to a current context of a current thread when said object's scope is created; means for resetting said object's scope's owner to a second thread's context when said second thread claims exclusive ownership of said scope; and means for setting said object's scope's owner to null when said ownership is shared.
6. An apparatus for locking an object having an ownership attribute, wherein a first thread having a first context makes a first request to a JavaScript engine at a first time, said first request comprising using said object, and a second thread having a second context makes a second request to the JavaScript engine at a second and later time, said second request comprising using said object, said method comprising: means for said JavaScript engine determining if said first request is finished with said object; if said first request is not finished with said object, then: means for said JavaScript engine comparing said second context of said second thread with said ownership attribute of said object; if said comparison is different, then means for suspending said second request until said first request is finished with said object; means for said JavaScript engine setting said ownership attribute of said object to null; means for said JavaScript engine resuming said second request; otherwise, means for said JavaScript engine setting said ownership attribute of said object to said second context and processing said second request.
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