patacongo edited a comment on issue #587: pthread_mutex_lock() does not resume waiting after signal URL: https://github.com/apache/incubator-nuttx/issues/587#issuecomment-601276937 NOTE: Passing the value false to pthread_mutex_take() is not a solution. That argument is passed to pthread_sem_take() and if the argument is false it calls: 117 if (abs_timeout == NULL) 118 { 119 ret = nxsem_wait_uninterruptible(sem); 120 } 121 else 122 { 123 ret = nxsem_timedwait_uninterruptible(sem, abs_timeout); 124 } But nxsem_wait_uninterruptble does more than just ignore signal interrupts: 544 static inline int nxsem_wait_uninterruptible(FAR sem_t *sem) 545 { 546 int ret; 547 548 do 549 { 550 /* Take the semaphore (perhaps waiting) */ 551 552 ret = nxsem_wait(sem); 553 } 554 while (ret == -EINTR || ret == -ECANCELED); 555 556 return ret; 557 } It also breaks thread cancellation. When cancellation points are enabled, semaphore waits will be awakened with ECANCELED and must return. In the deferred cancellation mode all resources will be cleaned-up and that task will terminated when it attempts to exit the cancellation point. Since the loop prevents the task from exiting the cancellation point, it will prent the task from being terminated. The above breaks thread cancellation because in the event that the thread is cancelled, it simply loops back and waits again. The thread cannot be cancelled in the recommended deferred cancellation most. That is seriaous OS breakage. This is a bug in the existing implementation. ALL semaphore waits must return in the event of thread cancellation, otherwise thread cancellation is broken (it is broken in many cases). A better solution in pthread_sem_take() would be to set up a sigprocmask and block relevant signals instead of calling nxsem_wait_uninterruptible(). That is too brutal. All signals should be blocked except (1) the signal that wakes up the timed event and (2) any signals associated with thread cancellation.
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