Memory leaks

In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations in such a way that memory which is no longer needed is not released. In object-oriented programming, a memory leak may happen when an object is stored in memory but cannot be accessed by the running code. A memory leak has symptoms similar to a number of other problems and generally can only be diagnosed by a programmer with access to the program's source code.

A space leak occurs when a computer program uses more memory than necessary. In contrast to memory leaks, where the leaked memory is never released, the memory consumed by a space leak is released, but later than expected.

Because they can exhaust available system memory as an application runs, memory leaks are often the cause of or a contributing factor to software aging.

A memory leak reduces the performance of the computer by reducing the amount of available memory. Eventually, in the worst case, too much of the available memory may become allocated and all or part of the system or device stops working correctly, the application fails, or the system slows down vastly due to thrashing.

Memory leaks may not be serious or even detectable by normal means. In modern operating systems, normal memory used by an application is released when the application terminates. This means that a memory leak in a program that only runs for a short time may not be noticed and is rarely serious.

Much more serious leaks include those:

The following example, written in pseudocode, is intended to show how a memory leak can come about, and its effects, without needing any programming knowledge. The program in this case is part of some very simple software designed to control an elevator. This part of the program is run whenever anyone inside the elevator presses the button for a floor.

The memory leak would occur if the floor number requested is the same floor that the elevator is on; the condition for releasing the memory would be skipped. Each time this case occurs, more memory is leaked.

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