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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



thr_suspend, thr_continue - suspend or continue thread execution


#include <thread.h> 

int thr_suspend(thread_t target_thread);
int thr_continue(thread_t target_thread);


The thr_suspend() function immediately suspends the execution of the thread specified by target_thread. On successful return from thr_suspend(), the suspended thread is no longer executing. Once a thread is suspended, subsequent calls to thr_suspend() have no effect.

The thr_continue() function resumes the execution of a suspended thread. Once a suspended thread is continued, subsequent calls to thr_continue() have no effect.

A suspended thread will not be awakened by any mechanism other than a call to thr_continue(). Signals and the effect of calls to mutex_unlock(3C), rw_unlock(3C), sema_post(3C), cond_signal(3C), and cond_broadcast(3C) remain pending until the execution of the thread is resumed by thr_continue().

Return Values

If successful, the thr_suspend() and thr_continue() functions return 0. Otherwise, a non-zero value is returned to indicate the error. It is not an error for the target thread to be a zombie thread.


The thr_suspend() and thr_continue() functions will fail if:


The target_thread cannot be found in the current process.


See attributes(7) for descriptions of the following attributes:


See Also

thr_create(3C), thr_join(3C), attributes(7), standards(7)


The thr_suspend() function is extremely difficult to use safely because it suspends the target thread with no concern for the target thread's state. The target thread could be holding locks, waiting for a lock, or waiting on a condition variable when it is unconditionally suspended. The thread will not run until thr_continue() is applied, regardless of any calls to mutex_unlock(), cond_signal(), or cond_broadcast() by other threads. Its existence on a sleep queue can interfere with the waking up of other threads that are on the same sleep queue.

The thr_suspend() and thr_continue() functions should be avoided. Mechanisms that involve the cooperation of the targeted thread, such as mutex locks and condition variables, should be employed instead.