code snippet to quickly test if an API is cancellable

cancelling a thread may have unexpected results, E.g., memory leak, dangling mutex, global state inconsistency ect.

However, there still are scenarios that you need to check if a long lasting blocking API is cancellable or not, below code can test that quickly:

#include <pthread.h>

#include <stdio.h>

#include <errno.h>

#include <stdlib.h>

#include <unistd.h>

#define handle_error_en(en, msg) \

do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

static void *

thread_func(void *ignored_argument)

{

int s;

int a = 0;

char buf[1024];

/* Disable cancellation for a while, so that we don't

immediately react to a cancellation request */

s = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, NULL);

if (s != 0)

handle_error_en(s, "pthread_setcancelstate");

printf("thread_func(): started; cancellation disabled\n");

sleep(5);

printf("thread_func(): about to enable cancellation\n");

s = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);

if (s != 0)

handle_error_en(s, "pthread_setcancelstate");

s = pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);

if (s != 0)

handle_error_en(s, "pthread_setcanceltype");

/* block on a long lasting blocking call */

// put your blocking call API here, e.g., sleep a long time */

/* Should never get here */

printf("thread_func(): not canceled!\n");

return NULL;

}

int

main(void)

{

pthread_t thr;

void *res;

int s;

/* Start a thread and then send it a cancellation request */

s = pthread_create(&thr, NULL, &thread_func, NULL);

if (s != 0)

handle_error_en(s, "pthread_create");

sleep(2); /* Give thread a chance to get started */

printf("main(): sending cancellation request\n");

s = pthread_cancel(thr);

if (s != 0)

handle_error_en(s, "pthread_cancel");

/* Join with thread to see what its exit status was */

s = pthread_join(thr, &res);

if (s != 0)

handle_error_en(s, "pthread_join");

if (res == PTHREAD_CANCELED)

printf("main(): thread was canceled\n");

else

printf("main(): thread wasn't canceled (shouldn't happen!)\n");

exit(EXIT_SUCCESS);

}