90e77cc3a0
Tell all waiters that something bad happened and they should all go away. Can be used only once; waiters should clean up and there must not be any new waiters.
81 lines
2.3 KiB
C++
81 lines
2.3 KiB
C++
/*
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* Copyright (C) 2014 Cloudius Systems, Ltd.
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*/
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#ifndef CORE_SEMAPHORE_HH_
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#define CORE_SEMAPHORE_HH_
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#include "future.hh"
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#include "circular_buffer.hh"
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#include <stdexcept>
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class broken_semaphore : public std::exception {
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public:
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virtual const char* what() const noexcept {
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return "Semaphore broken";
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}
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};
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class semaphore {
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private:
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size_t _count;
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circular_buffer<std::pair<promise<>, size_t>> _wait_list;
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public:
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semaphore(size_t count = 1) : _count(count) {}
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future<> wait(size_t nr = 1) {
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if (_count >= nr && _wait_list.empty()) {
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_count -= nr;
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return make_ready_future<>();
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}
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promise<> pr;
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auto fut = pr.get_future();
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_wait_list.push_back({ std::move(pr), nr });
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return fut;
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}
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void signal(size_t nr = 1) {
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_count += nr;
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while (!_wait_list.empty() && _wait_list.front().second <= _count) {
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auto& x = _wait_list.front();
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_count -= x.second;
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x.first.set_value();
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_wait_list.pop_front();
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}
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}
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bool try_wait(size_t nr = 1) {
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if (_count >= nr && _wait_list.empty()) {
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_count -= nr;
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return true;
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} else {
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return false;
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}
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}
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size_t current() const { return _count; }
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// Signal to waiters that an error occured. wait() will see
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// an exceptional future<> containing a broken_semaphore exception.
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//
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// This may only be used once per semaphore; after using it the
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// semaphore is in an indeterminite state and should not be waited on.
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void broken() { broken(broken_semaphore()); }
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// Signal to waiters that an error occured. wait() will see
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// an exceptional future<> containing the provided exception parameter.
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//
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// This may only be used once per semaphore; after using it the
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// semaphore is in an indeterminite state and should not be waited on.
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template <typename Exception>
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void broken(const Exception& ex);
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};
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template <typename Exception>
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void semaphore::broken(const Exception& ex) {
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auto xp = std::make_exception_ptr(ex);
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while (!_wait_list.empty()) {
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auto& x = _wait_list.front();
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x.first.set_exception(xp);
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_wait_list.pop_front();
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}
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}
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#endif /* CORE_SEMAPHORE_HH_ */
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