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#include <threads.h>
#include <stdbool.h>
 
extern bool until_finish(void);
extern mtx_t lock;
extern cnd_t condition;
 
void func(void) {
  if (thrd_success != mtx_lock(&lock)) {
    /* Handle error */
  }

  while (until_finish()) {  /* Predicate does not hold */
    if (thrd_success != cnd_wait(&condition, &lock)) {
      /* Handle error */
    }
  }
 
  /* Resume when condition holds */

  if (thrd_success != mtx_unlock(&lock)) {
    /* Handle error */
  }
}

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This thread pauses execution using cnd_wait() and resumes when notified, presumably when the list has elements to be consumed. It is possible for the thread to be notified even if the list is still empty, perhaps because the notifying thread used cnd_broadcast(), which notifies all threads. Notification using cnd_broadcast() is frequently preferred over using cnd_signal(). (see See CON38-C. Preserve thread safety and liveness when using condition variables for more information.).

Note that a condition A condition predicate is typically the negation of the condition expression in the loop. In this noncompliant code example, the condition predicate for removing an element from a linked list is (list->next != NULL), whereas the condition expression for the while loop condition is (list->next == NULL).

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Failure to enclose calls to the cnd_wait() or cnd_timedwait() functions inside a while loop can lead to indefinite blocking and denial of service (DoS).

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website. 

Related Guidelines

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Bibliography

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Bibliography

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[Lea 2000]

1.3.2, "Liveness" 3.2.2, "Monitor Mechanics"

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