pthread sleep linux

Question

I am creating a program with multiple threads using pthreads.

Is sleep() causing the process (all the threads) to stop executing or just the thread where I am calling sleep?

Guimar

Answer 1

Just the thread. The POSIX documentation for sleep() says:

The sleep() function shall cause the calling thread to be suspended from execution...

Seismoscope

Here's what "man 3 sleep" says: "sleep() makes the calling process sleep until seconds seconds have elapsed..." (Ubuntu 10). The function is in unistd.h. Is this documentation wrong or is there a second sleep function? – Saucedo

@user48956: For historical reasons, the man pages often use "process" where the behaviour now applies to the "thread" - this is the case in the sleep(3) man page that you refer to. I suggest submitting a bug to Ubuntu about the documentation. – Seismoscope

Answer 2

Try this,

#include <unistd.h>

usleep(microseconds);

Etherealize

Yep, that's easier to use than nanosleep in most cases. – Vuillard

Note that usleep() is obsolete and has been removed from POSIX.1-2008. You should use either sleep(), or nanosleep() if higher resolution is required. – Getaway

Answer 3

I usually use nanosleep and it works fine. Nanosleep supends the execution of the calling thread. I have had the same doubt because in some man pages sleep refers to the entire process.

Middleweight

Answer 4

In practice, there are few cases where you just want to sleep for a small delay (milliseconds). For Linux, read time(7), and see also this answer. For a delay of more than a second, see sleep(3), for a small delay, see nanosleep(2). (A counter example might be a RasPerryPi running some embedded Linux and driving a robot; in such case you might indeed read from some hardware device every tenth of seconds). Of course what is sleeping is just a single kernel-scheduled task (so a process or thread).

It is likely that you want to code some event loop. In such a case, you probably want something like poll(2) or select(2), or you want to use condition variables (read a Pthread tutorial about pthread_cond_init etc...) associated with mutexes.

Threads are expensive resources (since each needs a call stack, often of a megabyte at least). You should prefer having one or a few event loops instead of having thousands of threads.

If you are coding for Linux, read also Advanced Linux Programming and syscalls(2) and pthreads(7).

Templeton

Answer 5

Posix sleep function is not thread safe. https://clang.llvm.org/extra/clang-tidy/checks/concurrency/mt-unsafe.html

Returnee

Answer 6

sleep() function does not cease a specific thread, but it stops the whole process for the specified amount of time. For stopping the execution of a particular thread, we can use one pthread condition object and use pthread_cond_timedwait() function for making the thread wait for a specific amount of time. Each thread will have its own condition object and it will never receive a signal from any other thread.

Nahuatlan

This is inaccurate. The sleep() will cause the current thread to sleep. See sleep(3). Lots of older man pages still use the word "process," but in reality a thread is a process. – Wilcox