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log in contents move to sidebar hide top 1 description 2 manual memory management techniques 3 manual management and correctness 4 resource acquisition is initialization 5 defer toggle defer subsection 5 1 c 5 2 go 5 3 zig 6 performance 7 see also 8 references 9 external links toggle the table of contents manual memory management 1 language العربية edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia computer memory management methodology this article has multiple issues please help improve it or discuss these issues on the talk page learn how and when to remove these messages this article relies on a single source please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed find sources manual memory management news newspapers books scholar jstor june 2009 learn how and when to remove this message this article only references primary sources please improve this article by adding secondary or tertiary sources unsourced material may be challenged and removed find sources manual memory management news newspapers books scholar jstor july 2018 learn how and when to remove this message this article includes a list of general references but lacks sufficient corresponding inline citations please help improve this article by introducing more precise citations july 2018 learn how and when to remove this message learn how and when to remove this message in computer science manual memory management refers to the usage of manual instructions by the programmer to identify and deallocate unused objects or garbage up until the mid 1990s the majority of programming languages used in industry supported manual memory management though garbage collection has existed since 1959 when it was introduced with lisp 1 today however languages with garbage collection such as java are increasingly popular and the languages objective c and swift provide similar functionality through automatic reference counting the main manually managed languages still in widespread use today are c and c see c dynamic memory allocation description edit many programming languages use manual techniques to determine when to allocate a new object from the free store c uses the malloc function c and java use the new operator and many other languages such as python allocate all objects from the free store determining when an object ought to be created object creation is generally trivial and unproblematic though techniques such as object pools mean an object may be created before immediate use the real challenge is object destruction determination of when an object is no longer needed i e is garbage and arranging for its underlying storage to be returned to the free store for re use in manual memory allocation this is also specified manually by the programmer via functions such as free in c or the delete operator in c this contrasts with automatic destruction of objects held in automatic variables notably non static local variables of functions which are destroyed at the end of their scope in c and c manual memory management techniques edit this section needs expansion you can help by adding missing information january 2022 for example malloc and free or new and delete memory arena scratch buffer resource acquisition is initialization the pattern of tying an object s ownership of resources to its lifetime defer the act of deferring or postponing cleanup until the end of a function call manual management and correctness edit main article memory safety manual memory management is known to enable several major classes of bugs into a program when used incorrectly notably violations of memory safety or memory leaks these are a significant source of security bugs 2 when an unused object is never released back to the free store this is known as a memory leak in some cases memory leaks may be tolerable such as a program which leaks a bounded amount of memory over its lifetime or a short running program which relies on an operating system to deallocate its resources when it terminates however in many cases memory leaks occur in long running programs and in such cases an unbounded amount of memory is leaked when this occurs the size of the available free store continues to decrease over time when it is finally exhausted the program then crashes catastrophic failure of the dynamic memory management system may result when an object s backing memory is deleted out from under it more than once an object is explicitly destroyed more than once when while using a pointer to manipulate an object not allocated on the free store a programmer attempts to release said pointer s target object s backing memory or when while manipulating an object via a pointer to another arbitrary area of memory managed by an unknown external task thread or process a programmer corrupts that object s state possibly in such a way as to write outside of its bounds and corrupt its memory management data the result of such actions can include heap corruption premature destruction of a different and newly created object which happens to occupy the same location in memory as the multiply deleted object program crashes due to a segmentation fault violation of memory protection and other forms of undefined behavior pointers to deleted objects become wild pointers if used post deletion attempting to use such pointers can result in difficult to diagnose bugs languages which exclusively use garbage collection are known to avoid the last two classes of defects memory leaks can still occur and bounded leaks frequently occur with generational or conservative garbage collection but are generally less severe than memory leaks in manual systems resource acquisition is initialization edit main article resource acquisition is initialization manual memory management has one correctness advantage which is that it allows automatic resource management via the resource acquisition is initialization raii paradigm this arises when objects own scarce system resources like graphics resources file handles or database connections which must be relinquished when an object is destroyed when the lifetime of the resource ownership should be tied to the lifetime of the object languages with manual management can arrange this by acquiring the resource during object initialization in the constructor and releasing during object destruction in the destructor which occurs at a precise time this is known as resource acquisition is initialization raii this can also be used with deterministic reference counting in c this ability is put to further use to automate memory deallocation within an otherwise manual framework use of smart pointers in the language s standard library to perform memory management is a common paradigm in languages like rust which enforce strict ownership raii becomes the default behavior for managing resources 3 this approach is not usable in most garbage collected languages notably tracing garbage collectors or more advanced reference counting due to finalization being non deterministic and sometimes not occurring at all that is it is difficult to define or determine when or if a finalizer method might be called this is commonly known as the finalizer problem java and other languages implementing a garbage collector frequently use manual management for scarce system resources besides memory via the dispose pattern any object which manages resources is expected to implement the dispose method which releases any such resources and marks the object as inactive programmers are expected to invoke dispose manually as appropriate to prevent leaking of scarce graphics resources for stack resources resources acquired and released within a single block of code this can be automated by various language constructs such as python s with c s using with resources which call an object s dispose method or java s try with resources usable on any object which implements java lang autocloseable and calls its close method defer edit a defer mechanism is a feature that allows the postponing of execution of a piece of code until later usually either the end of scope or end of a function this can be seen as similar to a finally block in other languages c edit c beginning in c29 introduces a defer mechanism each defer block which is encountered in execution is run at scope exit not when encountered in the reverse order they were encountered 4 include stddefer h include stdio h include stdlib h int processfile const char path file f fopen path r if f return 1 defer puts closing file fclose f char buffer malloc 1024 if buffer return 2 defer puts freeing buffer free buffer simulate multiple early exits if fgets buffer 1024 f return 3 both defers still run if buffer 0 return 4 both defers still run printf processing s n buffer return 0 c has not yet commented on whether or not it will integrate c defer as raii covers this use case go edit in go defer is used to schedule a function call to run when the surrounding function returns multiple defer s run in last in first out lifo order package main import fmt func main fmt println start defer fmt println first defer defer fmt println second defer fmt println end zig edit in zig defer is block level and runs when the current scope ends not just the function unlike go zig defer incurs no overhead const std import std pub fn main void std debug print start n defer std debug print inner defer n std debug print inside block n std debug print end n zig also includes errdefer which runs only if the function exits with an error performance edit many advocates of manual memory management argue that it affords superior performance when compared to automatic techniques such as garbage collection traditionally latency was the biggest advantage but this is no longer the case manual allocation frequently has superior locality of reference citation needed manual allocation is also known to be more appropriate for systems where memory is a scarce resource due to faster reclamation memory systems can and do frequently thrash as the size of a program s working set approaches the size of available memory unused objects in a garbage collected system remain in an unreclaimed state for longer than in manually managed systems because they are not immediately reclaimed increasing the effective working set size manual management has a number of documented performance disadvantages calls to delete and such incur an overhead each time they are made this overhead can be amortized in garbage collection cycles this is especially true of multithreaded applications where delete calls must be synchronized the allocation routine may be more complicated and slower some garbage collection schemes such as those with heap compaction can maintain the free store as a simple array of memory as opposed to the complicated implementations required by manual management schemes latency is a debated point that has changed over time with early garbage collectors and simple implementations performing very poorly compared to manual memory management but sophisticated modern garbage collectors often performing as well or better than manual memory management citation needed manual allocation does not suffer from the long pause times that occur in simple stop the world garbage collection although modern garbage collectors have collection cycles which are often not noticeable citation needed manual memory management and garbage collection both suffer from potentially unbounded deallocation times manual memory management because deallocating a single object may require deallocating its members and recursively its members members etc while garbage collection may have long collection cycles this is especially an issue in real time systems where unbounded collection cycles are generally unacceptable real time garbage collection is possible by pausing the garbage collector while real time manual memory management requires avoiding large deallocations or manually pausing deallocation see also edit data segment memory management manual memory management references edit mccarthy john abrahams paul w edwards daniel j hart timothy p levin michael i 1985 1962 lisp 1 5 programmer s manual pdf 15th printing 2nd ed p preface c creator calls for action to address serious attacks archived from the original on 2026 01 14 retrieved 2026 01 16 the rust team 19 april 2026 raii rust by example doc rust lang org the rust team jeanheyd meneide 2025 programming c defer a mechanism for general purpose lexical scope based undo pdf open std org wg 14 berger e d zorn b g mckinley k s november 2002 reconsidering custom memory allocation pdf proceedings of the 17th acm sigplan conference on object oriented programming systems languages and applications oopsla 02 pp 1 12 doi 10 1145 582419 582421 isbn 1 58113 471 1 external links edit the memory management reference archived 2020 12 13 at the wayback machine richard jones and rafael lins garbage collection algorithms for automated dynamic memory management wiley and sons 1996 isbn 0 471 94148 4 v t e memory management memory management as a function of an operating system hardware memory management unit mmu translation lookaside buffer tlb input output memory management unit iommu virtual memory demand paging memory paging page table virtual memory compression segmentation protected mode real mode virtual 8086 mode x86 memory segmentation allocator dlmalloc hoard jemalloc libumem mimalloc ptmalloc manual means static memory allocation c dynamic memory allocation new and delete c garbage collection automatic reference counting boehm garbage collector cheney s algorithm concurrent mark sweep collector finalizer garbage garbage first collector mark compact algorithm reference counting tracing garbage collection strong reference weak reference safety buffer overflow buffer over read dangling pointer stack overflow issues fragmentation memory leak unreachable memory other automatic variable constructors destructors region based memory management memory pool memory management virtual memory automatic memory management memory management algorithms memory management software retrieved from https en wikipedia org w index php title manual_memory_management oldid 1374076853 category memory management hidden categories articles with short description short description is different from wikidata articles needing additional references from june 2009 all articles needing additional references articles lacking reliable references from july 2018 articles lacking in text citations from july 2018 all articles lacking 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