[metadata]
id = "CON36-C"
type = "rule"
category = "CON"
number = 36
title = "Wrap functions that can spuriously wake up in a loop"
description = """
Thecnd_wait()andcnd_timedwait()functionstemporarily cede possession of a mutex
so that other threads that may be requesting the mutex can proceed. These
functions must always be called from code that is protected by locking a mutex.
The waiting thread resumes execution only after it has been notified, generally
as the result of the invocation of thecnd_signal()orcnd_broadcast()function
invoked by another thread. Thecnd_wait()function must be invoked from a loop
that checks whether acondition predicateholds. A condition predicate is an
expression constructed from the variables of a function that must be true for a
thread to be allowed to continue execution. The thread pauses execution,
viacnd_wait(),cnd_timedwait(), or some other mechanism, and is resumed later,
presumably when the condition predicate is true and the thread is notified.
#include <threads.h> #include <stdbool.h> extern bool until_finish(void); extern
mtx_t lock; extern cnd_t condition; void func(void) { if (thrd_success !=
mtx_lock(&lock)) { /* Handle error */ } while (until_finish()) { /* Predicate
does not hold */ if (thrd_success != cnd_wait(&condition, &lock)) { /* Handle
error */ } } /* Resume when condition holds */ if (thrd_success !=
mtx_unlock(&lock)) { /* Handle error */ } } The notification mechanism notifies
the waiting thread and allows it to check its condition predicate. The
invocation ofcnd_broadcast()in another thread cannot precisely determine which
waiting thread will be resumed. Condition predicate statements allow notified
threads to determine whether they should resume upon receiving the notification.
"""
severity = "Low"
likelihood = "Unlikely"
priority = "P2"
level = "L3"
cert_version = "2016 Edition (Wiki)"
last_modified = "May 05, 2025"
[rules.cert_c.CON36-C]
enabled = true
[references]
wiki = "https://wiki.sei.cmu.edu/confluence/display/c/CON36-C.+Wrap+functions+that+can+spuriously+wake+up+in+a+loop"