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Thread execution starts at the beginning of the function func. To terminate the thread correctly, func must call _endthread or end with "return 0", freeing memory allocated by the run time library to support the thread.
Terminate – Abnormal termination of the process. The process is terminated with all the consequences of _exit() except that the status made available to wait() and waitpid() indicates abnormal termination by the specified signal.
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).
Furthermore, analogous context switching happens between user threads, notably green threads, and is often very lightweight, saving and restoring minimal context. In extreme cases, such as switching between goroutines in Go , a context switch is equivalent to a coroutine yield, which is only marginally more expensive than a subroutine call.
More generally, an exit in a multithreading environment means that a thread of execution has stopped running. For resource management, the operating system reclaims resources (memory, files, etc.) that were used by the process. The process is said to be a dead process after it terminates.
A critical section will usually terminate in finite time, [2] and a thread, task, or process must wait for a fixed time to enter it (bounded waiting). To ensure exclusive use of critical sections, some synchronization mechanism is required at the entry and exit of the program.
Take an example for thread, known as the thread barrier. The thread barrier needs a variable to keep track of the total number of threads that have entered the barrier. [3] Whenever there are enough threads enter the barrier, it will be lifted. A synchronization primitive like mutex is also needed when implementing the thread barrier.
Modern operating systems also provide system calls that allow a process's thread to create other threads and wait for them to terminate ("join" them) in a similar fashion. An operating system may provide variations of the wait call that allow a process to wait for any of its child processes to exit , or to wait for a single specific child ...