computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...

, a resource leak is a particular type of

resource Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon their ...

consumption by a

computer program A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...

where the program does not release resources it has acquired. This condition is normally the result of a bug in a program. Typical resource leaks include

memory leak In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations in a way that Computer memory, memory which is no longer needed is not released. A memory leak may also happe ...

and

handle leak A handle leak is a type of software bug that occurs when a computer program asks for a handle to a resource but does not free the handle when it is no longer used. If this occurs frequently or repeatedly over an extended period of time, a large ...

, particularly file handle leaks, though memory is often considered separately from other resources. Examples of resources available in limited numbers to the

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

include

internet socket The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

file handle In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier ( handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically hav ...

process table In computing, a process is the instance of a computer program that is being executed by one or many threads. There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are ro ...

entries, and

process identifier In computing, the process identifier (a.k.a. process ID or PID) is a number used by most operating system kernels—such as those of Unix, macOS and Windows—to uniquely identify an active process. This number may be used as a parameter in various ...

s (PIDs). Resource leaks are often a minor problem, causing at most minor slowdown and being recovered from after processes terminate. In other cases resource leaks can be a major problem, causing

resource starvation In computer science, resource starvation is a problem encountered in concurrent computing where a process is perpetually denied necessary resources to process its work. Starvation may be caused by errors in a scheduling or mutual exclusion algori ...

and severe system slowdown or instability, crashing the leaking process, other processes, or even the system. Resource leaks often go unnoticed under light load and short runtimes, and these problems only manifest themselves under heavy system load or systems that remain running for long periods of time.. Resource leaks are particularly a problem for resources available in very low quantities. Leaking a unique resource, such as a

lock Lock(s) may refer to: Common meanings *Lock and key, a mechanical device used to secure items of importance *Lock (water navigation), a device for boats to transit between different levels of water, as in a canal Arts and entertainment * ''Lock ...

, is particularly serious, as this causes immediate resource starvation (it prevents other processes from acquiring it) and causes

deadlock In concurrent computing, deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lo ...

. Intentionally leaking resources can be used in a

denial-of-service attack In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connect ...

, such as a

fork bomb In computing, a fork bomb (also called rabbit virus or wabbit) is a denial-of-service attack In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unav ...

, and thus resource leaks present a

security bug Security is protection from, or resilience against, potential harm (or other unwanted Coercion, coercive change) caused by others, by restraining the freedom of others to act. Beneficiaries (technically referents) of security may be of persons an ...

Causes

Resource leaks are generally due to programming errors: resources that have been acquired must be released, but since release often happens substantially after acquisition, and many things may occur in the meantime (e.g., an exception being thrown or abnormal program termination) it is easy for release to be missed. A very common example is failing to close files that have been opened, which leaks a file handle; this also occurs with

pipes Pipe(s), PIPE(S) or piping may refer to: Objects * Pipe (fluid conveyance), a hollow cylinder following certain dimension rules ** Piping, the use of pipes in industry * Smoking pipe ** Tobacco pipe * Half-pipe and quarter pipe, semi-circula ...

. Another common example is a

parent process In computing, a parent process is a process that has created one or more child processes. Unix-like systems In Unix-like operating systems, every process except (the swapper) is created when another process executes the fork() system call. Th ...

failing to call

wait Wait or WAIT may refer to: Music * Wait (musician), British town pipers Albums and EPs * ''Wait'' (The Polyphonic Spree EP), by The Polyphonic Spree * ''Wait'' (Emanuel Nice EP), a 2002 EP released by the band Emanuel Nice * ''Wait'' (Stee ...

on a

child process A child process in computing is a process created by another process (the parent process). This technique pertains to multitasking operating systems, and is sometimes called a subprocess or traditionally a subtask. There are two major procedures ...

, which leaves the completed child process as a

zombie process On Unix and Unix-like computer operating systems, a zombie process or defunct process is a process that has completed execution (via the exit system call) but still has an entry in the process table: it is a process in the " Terminated state". Thi ...

, leaking a

entry.

Prevention and mitigation

Resource leaks can be prevented or fixed by

resource management In organizational studies, resource management is the efficient and effective development of an organization's resources when they are needed. Such resources may include the financial resources, inventory, human skills, production resources, or i ...

: programming techniques or language constructs may prevent leaks by releasing resources promptly, while a separate process may reclaim resources that have been leaked. Many resource leaks are fixed by resource reclamation by the

after the process terminates and makes an

exit 
Exit(s) may refer to:
  Architecture and engineering 
* Door
* Portal (architecture), an opening in the walls of a structure
* Emergency exit
*  Overwing exit, a type of emergency exit on an airplane
* Exit ramp, a feature of a road  interchange
   ...

system call In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, acc ...

. Resource leaks are thus primarily a problem for long-lived processes, as leaked resources held by still-running processes are often not reclaimed; and for processes that rapidly acquire and leak many resources.

References

{{reflist Computational resources

Causes

Prevention and mitigation

See also

References