danicoin/external/glim/channel.hpp
Thomas Winget 90d6f8bf62 Adding libglim as an external library
libglim is an Apache-licensed C++ wrapper for lmdb, and rather than
rolling our own it seems prudent to use it.

Note: lmdb is not included in it, and unless something happens as did
with libunbound, should be installed via each OS' package manager or
equivalent.
2015-01-04 18:41:44 -08:00

40 lines
1.1 KiB
C++

#ifndef _GLIM_CHANNEL_INCLUDED
#define _GLIM_CHANNEL_INCLUDED
#include <atomic>
#include <mutex>
#include <thread>
namespace glim {
/// Unbuffered channel.
/// Optimized for a single value (busy-waits on a second one).
template <typename V>
struct Channel {
V _v;
std::mutex _mutex; // Locked when there is no value.
std::atomic_int_fast8_t _state; enum State {EMPTY = 0, WRITING = 1, FULL = 2};
Channel(): _state (EMPTY) {_mutex.lock();}
// Waits until the Channel is empty then stores the value.
template <typename VA> void send (VA&& v) {
for (;;) {
int_fast8_t expectEmpty = EMPTY; if (_state.compare_exchange_weak (expectEmpty, WRITING)) break;
std::this_thread::sleep_for (std::chrono::milliseconds (20));
}
try {_v = std::forward<V> (v);} catch (...) {_state = EMPTY; throw;}
_state = FULL;
_mutex.unlock(); // Allows the reader to proceed.
}
// Waits untill there is a value to receive.
V receive() {
_mutex.lock(); // Wait.
V tmp = std::move (_v);
assert (_state == FULL);
_state = EMPTY;
return tmp;
}
};
} // namespace glim
#endif