I have a situation where I would like to cancel a thread if it requires too much to complete. To do this, I use the second thread, which waits for the completion of the first thread, but not more than a few seconds. The pthread_cond_timedwait () function seems to be ideal for my use case, however, it does not seem to behave as I expected. More specifically, even though the pthread_cond_timedwait () function returns ETIMEDOUT, it only does this after the thread that was supposed to cancel completion, which is detrimental to the whole target.
This is my test code:
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <iostream>
#include <cstring>
#define WAIT_INTERVAL 5
#define THREAD_SLEEP 10
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condition = PTHREAD_COND_INITIALIZER;
pthread_t t1;
pthread_t t2;
void* f1(void*);
void* f2(void*);
int main()
{
pthread_create(&t1, NULL, &f1, NULL);
pthread_create(&t2, NULL, &f2, NULL);
pthread_join(t1, NULL);
pthread_join(t2, NULL);
std::cout << "Thread(s) successfully finished" << std::endl << std::flush;
exit(EXIT_SUCCESS);
}
void* f1(void*)
{
pthread_mutex_lock(&mutex);
timespec ts = {0};
clock_gettime(CLOCK_REALTIME, &ts);
ts.tv_sec += WAIT_INTERVAL;
std::cout << __FUNCTION__ << ": Waiting for at most " << WAIT_INTERVAL << " seconds starting now" << std::endl << std::flush;
int waitResult = pthread_cond_timedwait(&condition, &mutex, &ts);
if (waitResult == ETIMEDOUT)
{
std::cout << __FUNCTION__ << ": Timed out" << std::endl << std::flush;
int cancelResult = pthread_cancel(t2);
if (cancelResult)
{
std::cout << __FUNCTION__ << ": Could not cancel T2 : " << strerror(cancelResult) << std::endl << std::flush;
}
else
{
std::cout << __FUNCTION__ << ": Cancelled T2" << std::endl << std::flush;
}
}
std::cout << __FUNCTION__ << ": Finished waiting with code " << waitResult << std::endl << std::flush;
pthread_mutex_unlock(&mutex);
}
void* f2(void*)
{
pthread_mutex_lock(&mutex);
std::cout << __FUNCTION__ << ": Started simulating lengthy operation for " << THREAD_SLEEP << " seconds" << std::endl << std::flush;
sleep(THREAD_SLEEP);
std::cout << __FUNCTION__ << ": Finished simulation, signaling the condition variable" << std::endl << std::flush;
pthread_cond_signal(&condition);
pthread_mutex_unlock(&mutex);
}
The result obtained from the above code is as follows:
f1: Waiting for at most 5 seconds starting now
f2: Started simulating lengthy operation for 10 seconds
f2: Finished simulation, signaling the condition variable
f1: Timed out
f1: Could not cancel T2 : No such process
f1: Finished waiting with code 110
Thread(s) successfully finished
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POSIX CentOS 6.5. :
2.6.32-431.5.1.el6.centos.plus.x86_64 # 1 SMP x86_64 x86_64 x86_64 GNU/Linux
g++ (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4)
: g++ -o executable_binary -pthread -lrt source_code.cpp