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Schematic representation of how threads work under GIL. Green - thread holding GIL, red - blocked threads. A global interpreter lock (GIL) is a mechanism used in computer-language interpreters to synchronize the execution of threads so that only one native thread (per process) can execute basic operations (such as memory allocation and reference counting) at a time. [1]
This program creates five threads, each executing the function perform_work that prints the unique number of this thread to standard output. If a programmer wanted the threads to communicate with each other, this would require defining a variable outside of the scope of any of the functions, making it a global variable .
In both cases, the features must be part of the language syntax and not an extension such as a library (libraries such as the posix-thread library implement a parallel execution model but lack the syntax and grammar required to be a programming language).
Instead of waiting for the stall to resolve, a threaded processor would switch execution to another thread that was ready to run. Only when the data for the previous thread had arrived, would the previous thread be placed back on the list of ready-to-run threads. For example: Cycle i: instruction j from thread A is issued.
This approach does not work on multiprocessor systems where it is possible for two programs sharing a semaphore to run on different processors at the same time. To solve this problem in a multiprocessor system, a locking variable can be used to control access to the semaphore. The locking variable is manipulated using a test-and-set-lock command.
Thread Control Block (TCB) is a data structure in an operating system kernel that contains thread-specific information needed to manage the thread. [1] The TCB is "the manifestation of a thread in an operating system." Each thread has a thread control block. An operating system keeps track of the thread control blocks in kernel memory. [2]
There is a Win32 Thread Information Block for each thread. One of the entries in this block is the thread-local storage table for that thread. [1] Each call of TlsAlloc returns a unique index into this table. Each thread can independently use TlsSetValue(index, value) and obtain the specified value via TlsGetValue(index), because these set and ...
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.