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The C Standard, 7.26.5.6 [ISO/IEC 9899:2011], states that a thread shall not be joined once it was previously joined or detached. Similarly, subclause 7.26.5.3 states that a thread shall not be detached once it was previously joined or detached. Violating either of these subclauses results in undefined behavior.

Noncompliant Code Example

This noncompliant code example detaches a thread that is later joined.

#include <stddef.h>
#include <threads.h>
 
int thread_func(void *arg) {
  /* Do work */
  thrd_detach(thrd_current());
  return 0;
}

int main(void) {
  thrd_t t;

  if (thrd_success != thrd_create(&t, thread_func, NULL)) {
    /* Handle error */
    return 0;
  }

  if (thrd_success != thrd_join(t, 0)) {
    /* Handle error */
    return 0;
  }
  return 0;
}

Compliant Solution

 This compliant solution does not detach the thread. Its resources are released upon successfully joining with the main thread:

#include <stddef.h>
#include <threads.h>
  
int thread_func(void *arg) {
  /* Do work */
  return 0;
}

int main(void) {
  thrd_t t;

  if (thrd_success != thrd_create(&t, thread_func, NULL)) {
    /* Handle error */
    return 0;
  }

  if (thrd_success != thrd_join(t, 0)) {
    /* Handle error */
    return 0;
  }
  return 0;
} 

Risk Assessment

Joining or detaching a previously joined or detached thread is undefined behavior.

Rule

Severity

Likelihood

Remediation Cost

Priority

Level

CON39-C

Low

Likely

Medium

P6

L2

Automated Detection

Tool

Version

Checker

Description

Astrée
19.04

Supported, but no explicit checker
Parasoft C/C++test

10.4.2

CERT_C-CON39-a

Do not join or detach a thread that was previously joined or detached

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Bibliography

[ISO/IEC 9899:2011]

Subclause 7.26.5.3, "The thrd_detach Function"
Subclause 7.26.5.6, "The thrd_join Function"



1 Comment

  1. There seem to be alot of undefined behaviors in C11 dealing with threading that aren't explicitlly listed in Annex J:

    The C Standard, subclause 7.26.5.6 [ISO/IEC 9899:2011], specifically states that a thread shall not be joined once it was previously joined or detached. Similarly, subclause 7.26.5.3 states that a thread shall not be detached once it was previously joined or detached.