Page History

...

Blocking calls include, but are not limited to: network, file, and console I/O. This rule is a specific instance of CON36CON05-C. Do not perform operations that can block while holding a lock using POSIX threads.

Noncompliant Code Example

...

void thread_foo(void *ptr) {
  uint32_t num;
  int result;
  int sock;

  /* sock is a connected TCP socket */

  if ((result = recv(sock, (void *)&num, sizeof(uint32_t), 0)) < 0) {
    /* Handle Error */
  }

  if ((result = pthread_mutex_lock(&mutex)) != 0) {
    /* Handle Error */
  }

  /* ... */

  if ((result = pthread_mutex_unlock(&mutex)) != 0) {
    /* Handle Error */
  }
}

Compliant Solution (Use a

...

Nonblocking Call)

This compliant solution performs the recv() call with the parameter oMSG_nonblockDONTWAIT, which causes the call to fail if no messages are available on the socket:

void thread_foo(void *ptr) {
  uint32_t num;
  int result;

  /* sock is a connected TCP socket */

  if ((result = recv(sock, (void *)&num, sizeof(uint32_t), OMSG_NONBLOCKDONTWAIT)) < 0) {
    /* Handle Error */
  }

  if ((result = pthread_mutex_lock(&mutex)) != 0) {
    /* Handle Error */
  }

  /* ... */

  if ((result = pthread_mutex_unlock(&mutex)) != 0) {
    /* Handle Error */
  }
}

Exceptions

POS52-C-EX1: A thread may block while holding one or more locks and waiting to acquire another lock. When acquiring multiple locks, the order of locking must avoid deadlock, as specified in CON35-C. Avoid deadlock by locking in a predefined order.

...

Blocking or lengthy operations performed within synchronized regions could result in a deadlocked or an unresponsive system.

Automated Detection

Related Guidelines

Key here (explains table format and definitions)

CERT-CWE Mapping Notes

Key here for mapping notes

CWE-557 and POS52-C

CWE-557 = Union( POS52-C, list) where list =

• Concurrency issues besides blocking while holding a POSIX lock

Bibliography

...

...

Image ModifiedImage ModifiedImage Modified