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.
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; } |
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; } |
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 |
Tool | Version | Checker | Description |
---|---|---|---|
Astrée | Supported, but no explicit checker | ||
CodeSonar | CONCURRENCY.TNJ | Thread is not Joinable | |
Helix QAC | C1776 | ||
Parasoft C/C++test | CERT_C-CON39-a | Do not join or detach a thread that was previously joined or detached | |
Polyspace Bug Finder | CERT C: Rule CON39-C | Checks for join or detach of a joined or detached thread (rule fully covered) |
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
[ISO/IEC 9899:2011] | Subclause 7.26.5.3, "The |