Handle leaks occur when an application fails to close a handle to a system resource, leading to excessive consumption of finite computing resources and potential performance degradation or system crashes. Handles are managed by the OS through a handle table and can refer to memory or files. Troubleshooting tools can help programmers fight leaks, and monitoring handle count can diagnose leaks.
A handle leak is a type of resource leak, a situation in which a finite computing resource such as memory is consumed excessively by an application. Handle leaks occur when an application opens a “handle,” a special type of reference to a system resource, and fails to close that handle when it is no longer needed. They have the potential to degrade performance, cause application or system crashes, and can be a symptom of major bugs or sloppy coding in a software program. Many troubleshooting tools are available to programmers to help them fight leaks.
In computer programming, a handle is a structure that refers to a system resource, such as a block of memory or a file on a disk. Handles provide a layer of abstraction between system resources and applications and are typically managed by a computer’s operating system through a “handle table” that associates each handle with a resource. A programmer could use a handle to refer to a window which is then drawn to the screen by the operating system.
A well-mannered application will release handles it no longer requires, freeing up resources and ensuring that the OS doesn’t end up handling a resource that isn’t in use. Programming errors, software bugs, and software incompatibilities can cause programs to keep handles they no longer need. As the application continues to run, it may accumulate a large number of unnecessary handles. This is known as handle loss.
Handle leaks, like other types of resource leaks, can lead to slow performance, system instability, or, in extreme cases, a computer crash. This is because handles consume limited resources such as system memory, and if an application generates too many handles without closing them, these resources become exhausted. The exact threshold at which a handle leak starts causing problems depends on your computer’s operating system, how much memory is available, and other factors. A leak where a few dozen handles are left open will likely go unnoticed by users, while a leak of ten thousand or more is a sign of a serious bug in the application code.
Programmers need to pay special attention to handling leaks, given their potential to cause problems. The easiest way to diagnose a handle leak is to look at the handle count, which is the number of handles currently open by a process or application while the application is running. The Windows® Task Manager can display this information, and third-party utilities for Windows® and other operating systems can also be useful in identifying and tracking leaking handles.
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