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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:nil -*-
#pragma once
#include "common/ceph_mutex.h"
#include <thread>
#include <string>
namespace ceph {
/// a FIFO mutex
class fair_mutex {
public:
fair_mutex(const std::string& name)
: mutex{ceph::make_mutex(name)}
{}
~fair_mutex() = default;
fair_mutex(const fair_mutex&) = delete;
fair_mutex& operator=(const fair_mutex&) = delete;
void lock()
{
std::unique_lock lock(mutex);
const unsigned my_id = next_id++;
cond.wait(lock, [&] {
return my_id == unblock_id;
});
_set_locked_by();
}
bool try_lock()
{
std::lock_guard lock(mutex);
if (is_locked()) {
return false;
}
++next_id;
_set_locked_by();
return true;
}
void unlock()
{
std::lock_guard lock(mutex);
++unblock_id;
_reset_locked_by();
cond.notify_all();
}
bool is_locked() const
{
return next_id != unblock_id;
}
#ifdef CEPH_DEBUG_MUTEX
bool is_locked_by_me() const {
return is_locked() && locked_by == std::this_thread::get_id();
}
private:
void _set_locked_by() {
locked_by = std::this_thread::get_id();
}
void _reset_locked_by() {
locked_by = {};
}
#else
void _set_locked_by() {}
void _reset_locked_by() {}
#endif
private:
unsigned next_id = 0;
unsigned unblock_id = 0;
ceph::condition_variable cond;
ceph::mutex mutex;
#ifdef CEPH_DEBUG_MUTEX
std::thread::id locked_by = {};
#endif
};
} // namespace ceph
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