rspec/rules/S5486/rule.adoc

_Mutexes_ are synchronization primitives that allow to manage concurrency.

* _non recursive mutexes_ are targeted by this rule. They can be locked/unlocked only once. Any locking/unlocking sequence that contains two consecutive identical operations leads to an undefined behaviour.
* _recursive mutexes_ are not target by this rule.  They can be locked several times and unlocked several times as long as the number of locks/unlocks is the same.

This rule raises an issue when a ``++pthread_mutex_t++`` is locked or unlocked several times in a row. We assume that all ``++pthread_mutex_t++`` are non-recursive (this is the most common case).


== Noncompliant Code Example

----
pthread_mutex_t mtx1;

void bad1(void)
{
  pthread_mutex_lock(&mtx1);
  pthread_mutex_lock(&mtx1);
}

void bad2(void)
{
  pthread_mutex_unlock(&mtx1);
  pthread_mutex_unlock(&mtx1);
}
----


== Compliant Solution

----
pthread_mutex_t mtx1;

void ok(void)
{
  pthread_mutex_lock(&mtx1);
  pthread_mutex_unlock(&mtx1);
}
----


== See

* https://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_mutex_destroy.html[The Open Group] pthread_mutex_init, pthread_mutex_destroy