MISRA C:2023 Rule 21.26

The Standard Library function mtx_timedlock() shall only be invoked on mutex objects of appropriate mutex type

Since R2025b

Description

Rule Definition

The Standard Library function mtx_timedlock() shall only be invoked on mutex objects of appropriate mutex type.¹

Rationale

The function mtx_timedlock() should only be used on mutexes that support a timeout functionality, specifically those initialized with the type mtx_timed or mtx_timed | mtx_recursive. Using mtx_timedlock() on a mutex initialized with other types, such as mtx_plain, results in undefined behavior.

For example, the following code results in undefined behavior:

mtx_t m;
mtx_init(&m, mtx_plain);
mtx_timedlock(&m, ts);

Polyspace Implementation

The rule checker reports a violation if a mutex of type mtx_t used by mtx_timedlock() was not previously initialized with type mtx_timed or mtx_timed | mtx_recursive.

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

Mutex That Does Not Support Timeout Used With mtx_locked()

In this example, the mutexes R2 and R4 are not initialized to support a timeout and therefore violate the rule.

#include <stdint.h>
#include <time.h>
#include <threads.h>

mtx_t R1;
mtx_t R2;
mtx_t R3;
mtx_t R4;

void init_mutexes(void) {
    mtx_init(&R1, mtx_timed);                    
    mtx_init(&R2, mtx_plain);                    
    mtx_init(&R3, mtx_timed | mtx_recursive);    
    mtx_init(&R4, mtx_plain | mtx_recursive);    
}

void lock_mutexes(struct timespec* ts) {
    mtx_timedlock(&R1, ts); // Compliant: R1 was initialized with mtx_timed
    mtx_timedlock(&R2, ts); // Noncompliant R2 was not initialized with mtx_timed
    mtx_timedlock(&R3, ts); // Compliant: R3 was initialized with mtx_timed | mtx_recursive
    mtx_timedlock(&R4, ts); // Noncompliant: R4 was not initialized with mtx_timed
}

int main(void) {
    struct timespec ts;
    init_mutexes();
    lock_mutexes(&ts);
    return 0;
}

Check Information

Group: Standard libraries

Category: Required

AGC Category: Required

Version History

Introduced in R2025b