It is both complicated and differs from Unix to Unix variant. In Linux, for example, a system called Futex (Short for Fast Userspace Mutex) is used. In this system an atomic increment and test operation is performed on the mutex variable in user space. If the result of the operation indicates that there was no … Read more
What? The person asked for Linux specific, and the equivalent of getpid(). Not BSD or Apple. The answer is gettid() and returns an integral type. You will have to call it using syscall(), like this: #include <sys/types.h> #include <unistd.h> #include <sys/syscall.h> …. pid_t x = syscall(__NR_gettid); While this may not be portable to non-linux systems, … Read more
If your goal is to have the main thread wait for all threads to reach the same point before continuing onward, I would suggest using pthread_barrier_wait: void worker(void*); int main(int argc, char **argv) { pthread_barrier_t b; pthread_t children[TCOUNT]; int child; /* +1 for our main thread */ pthread_barrier_init(&b, NULL, TCOUNT+1); for (child = 0; child … Read more
The POSIX equivalent for what you described is POSIX condition variables. Note that condition variable must always be used in pair with a POSIX mutex, but quite frequently several condition variables use the same mutex, so if you aren’t going to use the mutex exclusively for the condition variable, you shouldn’t place it in the … Read more
This is happening because once you pass a pointer to i you now have multiple threads using the same value. This causes a data race because the first thread is modifying i and your second thread is expecting it to never change. You can always allocate a temporary int and pass it to the thread … Read more
Yes, it is the signature of a nameless function pointer that takes and returns void *. If it had a name (as in a variable) it would be: void *(*myFuncName)(void*)
If you are running your application on Linux, you may be interested to know that: int pthread_tryjoin_np(pthread_t thread, void **retval); int pthread_timedjoin_np(pthread_t thread, void **retval, const struct timespec *abstime); Be careful, as the suffix suggests it, “np” means “non-portable”. They are not POSIX standard, gnu extensions, useful though. link to man page
There are several problems with your code: ptr is not initialised, so all the ptr-> parts will crash the program you are calling pthread_kill() immediately, very likely before the signal handler has been installed, and in a thread (which has unspecified behaviour) you call printf() from a signal handler, which is not guaranteed to work … Read more
A thread’s resources are not immediately released at termination, unless the thread was created with the detach state attribute set to PTHREAD_CREATE_DETACHED, or if pthread_detach is called for its pthread_t. An undetached thread will remain terminated state until its identifier is passed to pthread_join or pthread_detach. To sum it up, you have three options: create … Read more
You are right in saying that the order of thread execution is not sequential. To some extent, that is the whole point of using threads, i.e. to run other tasks concurrently. The output you are seeing is as expected, and can possibly be different. Perhaps this will help: main thread1 thread2 | |–create——–+———–\ | | … Read more