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Test Your Knowledge in Computers #906
Difficulty: Easy
A Unix shell repeatedly prints a prompt, waits for a command line on stdin, and then carries out some action, as directed by the contents of the command line.
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thr_suspend(3c) [opensolaris man page]

thr_suspend(3C) 					   Standard C Library Functions 					   thr_suspend(3C)

thr_suspend, thr_continue - suspend or continue thread execution SYNOPSIS
cc -mt [ flag... ] file...[ library... ] #include <thread.h> int thr_suspend(thread_t target_thread); int thr_continue(thread_t target_thread); DESCRIPTION
The thr_suspend() function immediately suspends the execution of the thread specified by target_thread. On successful return from thr_sus- pend(), 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_con- tinue() 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 tomu- tex_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. ERRORS
The thr_suspend() and thr_continue() functions will fail if: ESRCH The target_thread cannot be found in the current process. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
thr_create(3C), thr_join(3C), attributes(5), standards(5) WARNINGS
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. SunOS 5.11 22 Mar 2002 thr_suspend(3C)

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