C and C++ Binaries

CONCURRENCY.DL : Double Lock

Summary

A mutex has been locked twice, but there is no intervening unlock.

For broader checking for double-locking phenomena, enable warning classes Locked Twice and Missing Lock Release.

Properties

Class Name Double Lock
Significance reliability
Mnemonic CONCURRENCY.DL
Categories
MisraC2023 MisraC2023:22.18 Non-recursive mutexes shall not be recursively locked
  MisraC2023:D.4.1 Run-time failures shall be minimized
Misra2012 Misra2012:22.18 Non-recursive mutexes shall not be recursively locked
  Misra2012:D.4.1 Run-time failures shall be minimized
CWE CWE:764 Multiple Locks of a Critical Resource
Availability Available for C and C++.
Enabling Checks for this warning class are enabled by default. To disable them, add the following WARNING_FILTER rule to the project configuration file. 
WARNING_FILTER += discard class="Double Lock"

Triggering Functions

A warning is triggered if a lock acquisition function is called to acquire a mutex that has definitely already been acquired.

For the purpose of this check:

Example 

#include <pthread.h>

void dl_1(pthread_mutex_t lock){
  pthread_mutex_lock(&lock);
  pthread_mutex_lock(&lock);     /* 'Double Lock' warning issued here. */
}

void dl_2(pthread_mutex_t lock){
  pthread_mutex_lock(&lock);
  pthread_mutex_unlock(&lock);
  pthread_mutex_lock(&lock);     /* 'Double Lock' warning issued here - pthread_mutex_unlock()
                                  *  may have failed to release the lock.
                                  */
}

int no_dl(pthread_mutex_t lock){
  if (!pthread_mutex_lock(&lock)){return -1;}
  if (!pthread_mutex_unlock(&lock)){return -1;}
  return pthread_mutex_lock(&lock);                /* ok: if control reaches this line,
                                                    * the call to pthread_mutex_unlock() must have succeeded
                                                    */
}

Notes

Trying to lock an already-locked mutex can cause deadlock or undefined behavior.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.