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Unfortunately, this code contains a race condition, allowing the mutex to be destroyed before while it is unlockedstill owned, because start_threads() may invoke the lockmutex's destructor before all of the threads have finished using the lock. This behavior is undefined.exited.
| Code Block | ||||
|---|---|---|---|---|
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#include <mutex>
#include <thread>
const size_t max_threads = 10;
void do_work(size_t i, std::mutex *pm) {
std::lock_guard<std::mutex> guard(*pm);
// Access data protected by the lock.
}
void start_threads() {
std::thread threads[max_threads];
std::mutex m;
for (size_t i = 0; i < max_threads; ++i) {
threads[i] = std::thread(do_work, i, &m);
}
}
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This compliant solution eliminates the race condition by extending the lifetime of the lockmutex:
| Code Block | ||||
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#include <mutex>
#include <thread>
const size_t max_threads = 10;
void do_work(size_t i, std::mutex *pm) {
std::lock_guard<std::mutex> guard(*pm);
// Access data protected by the lock.
}
std::mutex m;
void start_threads() {
std::thread threads[max_threads];
for (size_t i = 0; i < max_threads; ++i) {
threads[i] = std::thread(do_work, i, &m);
}
}
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