HP-UX Reference (11i v3 07/02) - 3 Library Functions N-Z (vol 7)

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pthread_resume_np(3T) pthread_resume_np(3T)

(Pthread Library)

In either of the above conditions, it is strongly recommended to set the environment variable

PTHREAD_SUSPEND_SYNC

to 1 if the application uses

pthread_suspend()

which is not POSIX

compliant. Failing to do so, can lead to undeﬁned behavior.

RETURN VALUE

If successful,

pthread_continue()

, pthread_suspend()

and pthread_resume_np()

return

zero. Otherwise, an error number shall be returned to indicate the error (the

errno variable is not set).

ERRORS

If any of the following occur, the

pthread_suspend()

function returns the corresponding error

number.

[ESRCH] The target thread thread is not in the current process.

[EDEADLK] The target thread thread is the last running thread in the process. The operation

would result in deadlock for the process.

If any of the following occur, the

pthread_continue()

and pthread_resume_np()

functions

return the corresponding error number.

[ESRCH] The target thread thread is not in the current process.

[EINVAL] The value speciﬁed by ﬂags is invalid.

APPLICATION USAGE

This functionality enables a process that is multithreaded to temporarily suspend all activity to a single

thread of control. When the process is single threaded, the address space is not changing, and a consistent

view of the process can be gathered. One example of its use is for garbage collecting. The garbage collector

runs asynchronously within the process and assumes that the process is not changing while it is running.

Suspending a thread may have adverse effects on an application. If a thread is suspended while it holds a

critical resource, such as a mutex or a read-write lock, the application may stop or even deadlock until the

thread is continued. While the thread is suspended, other threads which may contend for the same resource

must block until the thread is continued. Depending on application behavior, this may even result in

deadlock. Application programmers are advised to either a) only suspend threads which call async-signal

safe functions or b) ensure that the suspending thread does not contend for the same resources that the

suspended thread may have acquired. Note: this includes resources that may be acquired by libraries.

The

pthread_suspend()

, pthread_continue(), and pthread_resume_np()

functions can-

not reliably be used for thread synchronization. Synchronization primitives like mutexes, semaphores,

read-write locks, and condition variables should be used instead.

AUTHOR

pthread_suspend()

and pthread_continue() were developed by X/Open.

pthread_resume_np()

was developed by HP.