MISRA C:2012 Rule 22.12

Thread objects, thread synchronization objects, and thread-specific storage pointers shall only be accessed by the appropriate Standard Library functions

Since R2025b

Description

Rule Definition

Thread objects, thread synchronization objects, and thread-specific storage pointers shall only be accessed by the appropriate Standard Library functions.¹

Rationale

The Standard Library provides designated functions for accessing thread objects, thread synchronization objects and thread-specific storage pointers. Direct manipulation of these objects without using the designated Standard Library functions can lead to situations where the behavior is undefined.

For instance:

• Functions such as thrd_create and thrd_join ensure that a thread object is unique for a given thread. Likewise, functions such as mtx_lock and mtx_unlock ensure that a thread synchronization object is unique for a given mutex. Direct copy or assignment of these objects violate the uniqueness and can lead to undefined behavior.

• To implement thread-specific storage, you create a new thread-specific storage key using the Standard Library function tss_create and then associate memory with this key using functions such as tss_set. If you directly manipulate the key in between the creation and the usage, the behavior is undefined.

Polyspace Implementation

The rule checker reports a violation if:

• Thread objects or objects of type thrd_t (declared in threads.h) are manipulated without using thrd_create, thrd_join, or similar Standard Library functions.

• Mutex objects or objects of type mtx_t (declared in threads.h) are manipulated without using mtx_lock, mtx_unlock, or similar Standard Library functions.

• Condition objects or objects of type cnd_t (declared in threads.h) are manipulated without using cnd_init, cnd_signal, or similar Standard Library functions.

• Thread-specific storage keys or objects of type tss_t (declared in threads.h) are manipulated without using tss_get, tss_set, or similar Standard Library functions.

The checker does not flag the uses of these objects with the sizeof or alignof operators.

Troubleshooting

If you expect a rule violation but Polyspace^® does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Accessing Thread Objects Without Using Standard Library Functions

In this example, the function manipulateThreads() illustrates various direct manipulations of thrd_t objects that violate the rule. The function accessThreadsUsingLibraryFunctions() shows thread object accesses that are compliant with the rule.

#include <threads.h>
thrd_t  thread1;
thrd_t  thread2;

int startFunc(void * data);
void thrd_unknown(thrd_t);

void manipulateThreads() {
  thrd_t* thp = &thread1;                         // Noncompliant
  thread1 = thread2;                              // Noncompliant
  thread2 = 0;                                    // Noncompliant
  if (thread1) {                                  // Noncompliant
    memset(&thread1, sizeof(thrd_t), 0);          // Noncompliant
  }
  if (thread1 == thread2) {                       // Noncompliant
    thrd_unknown(thread2);                        // Noncompliant
  }
}

void accessThreadsUsingLibraryFunctions() {
  if (thrd_create( &thread1, startFunc, "Thread data" )) {  // Compliant
    thrd_join(thread2, 0);                                  // Compliant   
  }
  if (thrd_equal(thread1, thread2)) {                       // Compliant    
    thrd_detach(thread1);                                   // Compliant 
  }
}

Check Information

Group: Resources

Category: Mandatory

AGC Category: Mandatory

Version History

Introduced in R2025b