Example - 1

The following function attempts to acquire a lock in order to perform operations on a shared resource.

// /* access shared resource */// 
pthread_mutex_lock(mutex);pthread_mutex_unlock(mutex);void f(pthread_mutex_t *mutex) {}

However, the code does not check the value returned by pthread_mutex_lock() for errors. If pthread_mutex_lock() cannot acquire the mutex for any reason, the function may introduce a race condition into the program and result in undefined behavior.

In order to avoid data races, correctly written programs must check the result of thread synchronization functions and appropriately handle all errors, either by attempting to recover from them or reporting them to higher levels.

return result;
// /* access shared resource */// 
int result;result = pthread_mutex_lock(mutex);if (0 != result)return pthread_mutex_unlock(mutex);int f(pthread_mutex_t *mutex) {}

Example - 2

The following code intends to fork a process, then have both the parent and child processes print a single line.

// /* Make timing window a little larger... */// 
putc(counter, stdout);fflush(stdout);sleep(1);char * word;int counter;for (word = string; counter = *word++; ) {}

exit(-2);
print("child\n");
print("PARENT\n");
pid_t pid;pid = fork();if (pid == -1) {}else if (pid == 0) {}else {}exit(0);static void print (char * string) {}int main(void) {}

One might expect the code to print out something like:

PARENTchild

However, because the parent and child are executing concurrently, and stdout is flushed each time a character is printed, the output might be mixed together, such as:

PcAhRiElNdT[blank line][blank line]