FIX: JScript leaks memory when an application repeatedly creates and destroys threads

If you use the Microsoft JScript engine on a thread and the thread is destroyed, approximately 150 bytes of heap memory are leaked. Typically, this behavior does not cause a problem. However, if an application repeatedly creates and destroys threads many times, and if the application uses JScript on those threads, the memory usage increase may be sufficient to decrease the performance of the system.

Software update information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

You must have Microsoft JScript 5.6 installed on the system before you apply this software update. Microsoft JScript 5.1 is not affected by this problem and does not require this software update.

Restart requirement

You do not have to restart your computer after you apply this software update if the JScript.dll file is not in use when you apply this software update.

Software update replacement Information

This software update does not replace any other software updates.

File information

The English version of this software update has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

To work around this problem, do not create and destroy large numbers of threads. When you use thread pools (when you reuse existing threads) you use the operating system more efficiently.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section of this article.

Microsoft is researching this problem and will post more information in this article when the information becomes available.

When you monitor the memory usage of an application, monitor both the Private Bytes and Virtual Bytes counters of the Process object in Performance Monitor. The memory that an application uses may increase and decrease significantly while the application runs. Valid reasons may exist that cause the memory that an application uses to increase over time.

To make sure that the problem that this article describes is causing a specific memory leak, you must repeat the suspected operation (in this case, creating a thread, using JScript on the thread, and then destroying the thread again) many thousands of times to determine whether the memory usage fluctuations are the program's typical behavior.

For additional information about the terminology that is used to describe Microsoft product updates, click the following article number to view the article in the Microsoft Knowledge Base: