A handle leak is a type of resource leak, a situation where an application over-consumes a finite computing resource, such as memory. Handle leaks occur when an application opens a “handle”, a special type of reference to a system resource, and does not close that handle when it is no longer needed. They have the potential to reduce performance, cause application or system crashes, and can be a symptom of serious bugs or sloppy coding in a software program. Many troubleshooting tools are available to developers to help them combat leaks.
A handle leak is a resource exhaustion problem that can cause computer system failure.
In computer programming, an identifier is a structure that refers to a system resource, such as a block of memory or a file on disk. Identifiers provide a layer of abstraction between system and application resources and are typically managed by a computer’s operating system through a “tag table” that matches each identifier to a resource. A programmer can use a handle to refer to a window that the operating system then draws on the screen.
A well-behaved application will release resources that are no longer needed, freeing up resources and ensuring that the operating system doesn’t end up managing 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 can accumulate a large number of unnecessary handles. This is known as a handle leak.
Dealing with 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 an excessive number of handles without closing them, those resources are exhausted. The exact threshold at which a handle leak begins to cause problems depends on the computer’s operating system, the amount of memory available, and other factors. Users are unlikely to notice a leak where a few dozen handles are left open, while a leak of ten thousand handles or more is a sign of a serious bug in the application code.
Programmers should pay special attention when it comes to leaks, given their potential to cause problems. The most basic method of diagnosing a handle leak is to look at the handle count, which is the number of handles that a process or application currently has open while the application is running. Windows® Task Manager can display this information, and third-party utilities for Windows® and other operating systems can also be helpful in identifying and tracking leaky handles.
