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Merge pull request #9684 from liamwhite/read-the-spec

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polyfill_thread: satisfy execution ordering requirements of stop_callback
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liamwhite 2023-01-29 09:35:42 -05:00 committed by GitHub
parent 9170387e71 619c0e70f0
commit d960723dc9
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 48 additions and 39 deletions
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77
src/common/polyfill_thread.h
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@ -41,17 +41,18 @@ bool StoppableTimedWait(std::stop_token token, const std::chrono::duration<Rep,
#include <chrono> #include <chrono>
#include <condition_variable> #include <condition_variable>
#include <functional> #include <functional>
#include <list> #include <map>
#include <memory> #include <memory>
#include <mutex> #include <mutex>
#include <optional> #include <optional>
#include <thread> #include <thread>
#include <type_traits> #include <type_traits>
#include <utility>
namespace std { namespace std {
namespace polyfill { namespace polyfill {
using stop_state_callbacks = list<function<void()>>; using stop_state_callback = size_t;
class stop_state { class stop_state {
public: public:
@ -59,61 +60,69 @@ public:
~stop_state() = default; ~stop_state() = default;
bool request_stop() { bool request_stop() {
stop_state_callbacks callbacks; unique_lock lk{m_lock};
{ if (m_stop_requested) {
scoped_lock lk{m_lock}; // Already set, nothing to do.
if (m_stop_requested.load()) {
// Already set, nothing to do
return false; return false;
} }
// Set as requested // Mark stop requested.
m_stop_requested = true; m_stop_requested = true;
// Copy callback list while (!m_callbacks.empty()) {
callbacks = m_callbacks; // Get an iterator to the first element.
} const auto it = m_callbacks.begin();
for (auto callback : callbacks) { // Move the callback function out of the map.
callback(); function<void()> f;
swap(it->second, f);
// Erase the now-empty map element.
m_callbacks.erase(it);
// Run the callback.
if (f) {
f();
}
} }
return true; return true;
} }
bool stop_requested() const { bool stop_requested() const {
return m_stop_requested.load(); unique_lock lk{m_lock};
return m_stop_requested;
} }
stop_state_callbacks::const_iterator insert_callback(function<void()> f) { stop_state_callback insert_callback(function<void()> f) {
stop_state_callbacks::const_iterator ret{}; unique_lock lk{m_lock};
bool should_run{};
{ if (m_stop_requested) {
scoped_lock lk{m_lock}; // Stop already requested. Don't insert anything,
should_run = m_stop_requested.load(); // just run the callback synchronously.
m_callbacks.push_front(f); if (f) {
ret = m_callbacks.begin();
}
if (should_run) {
f(); f();
} }
return 0;
}
// Insert the callback.
stop_state_callback ret = ++m_next_callback;
m_callbacks.emplace(ret, move(f));
return ret; return ret;
} }
void remove_callback(stop_state_callbacks::const_iterator it) { void remove_callback(stop_state_callback cb) {
scoped_lock lk{m_lock}; unique_lock lk{m_lock};
m_callbacks.erase(it); m_callbacks.erase(cb);
} }
private: private:
mutex m_lock; mutable recursive_mutex m_lock;
atomic<bool> m_stop_requested; map<stop_state_callback, function<void()>> m_callbacks;
stop_state_callbacks m_callbacks; stop_state_callback m_next_callback{0};
bool m_stop_requested{false};
}; };
} // namespace polyfill } // namespace polyfill
@ -223,7 +232,7 @@ public:
} }
~stop_callback() { ~stop_callback() {
if (m_stop_state && m_callback) { if (m_stop_state && m_callback) {
m_stop_state->remove_callback(*m_callback); m_stop_state->remove_callback(m_callback);
} }
} }
@ -234,7 +243,7 @@ public:
private: private:
shared_ptr<polyfill::stop_state> m_stop_state; shared_ptr<polyfill::stop_state> m_stop_state;
optional<polyfill::stop_state_callbacks::const_iterator> m_callback; polyfill::stop_state_callback m_callback;
}; };
template <typename Callback> template <typename Callback>