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This statement implies that destroying a mutex while a thread is waiting on it is undefined behavior.
Noncompliant Code Example
This noncompliant code example creates several threads that each invoke the do_work() function, passing a unique number as an ID.
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| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <mutex>
#include <thread>
const size_t max_threads = 10;
void do_work(size_t i, std::mutex *lockp)
{
std::lock_guard<std::mutex> guard(*lockp);
// Access data protected by the lock.
}
void start_threads(void)
{
std::thread threads[max_threads];
std::mutex lock;
for (size_t i = 0; i < max_threads; ++i) {
threads[i] = std::thread(do_work, i, &lock);
}
}
|
Compliant Solution
This compliant solution eliminates the race condition by extending the lifetime of the lock:
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <mutex>
#include <thread>
const size_t max_threads = 10;
void do_work(size_t i, std::mutex *lockp)
{
std::lock_guard<std::mutex> guard(*lockp);
// Access data protected by the lock.
}
std::mutex lock;
void start_threads(void)
{
std::thread threads[max_threads];
for (size_t i = 0; i < max_threads; ++i) {
threads[i] = std::thread(do_work, i, &lock);
}
}
|
Compliant Solution
This compliant solution eliminates the race condition by joining the threads before the lock's destructor is invoked:
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <mutex>
#include <thread>
const size_t max_threads = 10;
void do_work(size_t i, std::mutex *lockp)
{
std::lock_guard<std::mutex> guard(*lockp);
// Access data protected by the lock.
}
void run_threads(void)
{
std::thread threads[max_threads];
std::mutex lock;
for (size_t i = 0; i < max_threads; ++i) {
threads[i] = std::thread(do_work, i, &lock);
}
for (size_t i = 0; i < max_threads; ++i) {
threads[i].join();
}
} |
Risk Assessment
Destroying a mutex while it is locked may result in invalid control flow and data corruption.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
CON50-CPP | Medium | Probable | High | P4 | L3 |
Automated Detection
Tool | Version | Checker | Description |
|---|---|---|---|
5.0 |
| Can detect violations of this rule with CERT C Rule Pack | |
| Parasoft C/C++test | 9.5 | BD-RES-FREE, BD-RES-INVFREE |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
Bibliography
| [ISO/IEC 9899:2011] | 7.26.4.1, "The mtx_destroy Function" |
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