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• Critical_section abstract "In concurrent programming, a critical section is a piece of code that accesses a shared resource (data structure or device) that must not be concurrently accessed by more than one thread of execution. A critical section will usually terminate in fixed time, and a thread, task, or process will have to wait for a fixed time to enter it (aka bounded waiting). Some synchronization mechanism is required at the entry and exit of the critical section to ensure exclusive use, for example a semaphore.By carefully controlling which variables are modified inside and outside the critical section, concurrent access to that state is prevented. A critical section is typically used when a multithreaded program must update multiple related variables without a separate thread making conflicting changes to that data. In a related situation, a critical section may be used to ensure a shared resource, for example a printer, can only be accessed by one process at a time.How critical sections are implemented varies among operating systems.The simplest method is to prevent any change of processor control inside the critical section. On uni-processor systems, this can be done by disabling interrupts on entry into the critical section, avoiding system calls that can cause a context switch while inside the section, and restoring interrupts to their previous state on exit. Any thread of execution entering any critical section anywhere in the system will, with this implementation, prevent any other thread, including an interrupt, from being granted processing time on the CPU - and therefore from entering any other critical section or, indeed, any code whatsoever - until the original thread leaves its critical section.This brute-force approach can be improved upon by using semaphores. To enter a critical section, a thread must obtain a semaphore, which it releases on leaving the section. Other threads are prevented from entering the critical section at the same time as the original thread, but are free to gain control of the CPU and execute other code, including other critical sections that are protected by different semaphores.Some confusion exists in literature about the relationship between different critical sections in the same program. Clearly, a resource that must be protected from concurrent access must be accessible by several entry points in the code. If the resource were only accessible through a single entry point, then multithreaded processing would not be a necessary consideration. Each resource must be guarded by a common, "global" semaphore. Is each piece now a critical section, or are all the pieces guarded by the same semaphore in aggregate a single critical section? This confusion is evident in definitions of a critical section such as "... a piece of code that can only be executed by one process or thread at a time".".
• Critical_section wikiPageExternalLink ms682530.aspx.
• Critical_section wikiPageExternalLink parallel-programming-understanding-impact-critical-sections.html.
• Critical_section wikiPageID "638312".
• Critical_section wikiPageRevisionID "639649857".
• Critical_section hasPhotoCollection Critical_section.
• Critical_section subject Category:Concurrency_control.
• Critical_section subject Category:Programming_constructs.
• Critical_section type Abstraction100002137.
• Critical_section type Cognition100023271.
• Critical_section type Concept105835747.
• Critical_section type Content105809192.
• Critical_section type Idea105833840.
• Critical_section type ProgrammingConstructs.
• Critical_section type PsychologicalFeature100023100.
• Critical_section comment "In concurrent programming, a critical section is a piece of code that accesses a shared resource (data structure or device) that must not be concurrently accessed by more than one thread of execution. A critical section will usually terminate in fixed time, and a thread, task, or process will have to wait for a fixed time to enter it (aka bounded waiting).".
• Critical_section label "Critical section".
• Critical_section label "Kritická sekce".
• Critical_section label "Kritieke sectie".
• Critical_section label "Kritischer Abschnitt".
• Critical_section label "Região crítica".
• Critical_section label "Secció crítica".
• Critical_section label "Sección crítica".
• Critical_section label "Section critique".
• Critical_section label "Sekcja krytyczna".
• Critical_section label "Sezione critica".
• Critical_section label "Критическая секция".
• Critical_section label "クリティカルセクション".
• Critical_section label "임계 구역".
• Critical_section sameAs Kritická_sekce.
• Critical_section sameAs Kritischer_Abschnitt.
• Critical_section sameAs Sección_crítica.
• Critical_section sameAs Section_critique.
• Critical_section sameAs Sezione_critica.
• Critical_section sameAs クリティカルセクション.
• Critical_section sameAs 임계_구역.
• Critical_section sameAs Kritieke_sectie.
• Critical_section sameAs Sekcja_krytyczna.
• Critical_section sameAs Região_crítica.
• Critical_section sameAs m.02zf3_.
• Critical_section sameAs Q1046373.
• Critical_section sameAs Q1046373.
• Critical_section sameAs Critical_section.
• Critical_section wasDerivedFrom Critical_section?oldid=639649857.
• Critical_section isPrimaryTopicOf Critical_section.