+++ /dev/null
-// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
-// vim: ts=8 sw=2 smarttab
-
-#ifndef CEPH_COMMON_SHUNIQUE_LOCK_H
-#define CEPH_COMMON_SHUNIQUE_LOCK_H
-
-#include <mutex>
-#include <system_error>
-#include <boost/thread/shared_mutex.hpp>
-
-namespace ceph {
-// This is a 'lock' class in the style of shared_lock and
-// unique_lock. Like shared_mutex it implements both Lockable and
-// SharedLockable.
-
-// My rationale is thus: one of the advantages of unique_lock is that
-// I can pass a thread of execution's control of a lock around as a
-// parameter. So that methods further down the call stack can unlock
-// it, do something, relock it, and have the lock state be known by
-// the caller afterward, explicitly. The shared_lock class offers a
-// similar advantage to shared_lock, but each class is one or the
-// other. In Objecter we have calls that in most cases need /a/ lock
-// on the shared mutex, and whether it's shared or exclusive doesn't
-// matter. In some circumstances they may drop the shared lock and
-// reacquire an exclusive one. This could be handled by passing both a
-// shared and unique lock down the call stack. This is vexacious and
-// shameful.
-
-// Wanting to avoid heaping shame and vexation upon myself, I threw
-// this class together.
-
-// This class makes no attempt to support atomic upgrade or
-// downgrade. I don't want either. Matt has convinced me that if you
-// think you want them you've usually made a mistake somewhere. It is
-// exactly and only a reification of the state held on a shared mutex.
-
-/// Acquire unique ownership of the mutex.
-struct acquire_unique_t { };
-
-/// Acquire shared ownership of the mutex.
-struct acquire_shared_t { };
-
-constexpr acquire_unique_t acquire_unique { };
-constexpr acquire_shared_t acquire_shared { };
-
-template<typename Mutex>
-class shunique_lock {
-public:
- typedef Mutex mutex_type;
- typedef std::unique_lock<Mutex> unique_lock_type;
- typedef boost::shared_lock<Mutex> shared_lock_type;
-
- shunique_lock() noexcept : m(nullptr), o(ownership::none) { }
-
- // We do not provide a default locking/try_locking constructor that
- // takes only the mutex, since it is not clear whether to take it
- // shared or unique. We explicitly require the use of lock_deferred
- // to prevent Nasty Surprises.
-
- shunique_lock(mutex_type& m, std::defer_lock_t) noexcept
- : m(&m), o(ownership::none) { }
-
- shunique_lock(mutex_type& m, acquire_unique_t)
- : m(&m), o(ownership::none) {
- lock();
- }
-
- shunique_lock(mutex_type& m, acquire_shared_t)
- : m(&m), o(ownership::none) {
- lock_shared();
- }
-
- template<typename AcquireType>
- shunique_lock(mutex_type& m, AcquireType at, std::try_to_lock_t)
- : m(&m), o(ownership::none) {
- try_lock(at);
- }
-
- shunique_lock(mutex_type& m, acquire_unique_t, std::adopt_lock_t)
- : m(&m), o(ownership::unique) {
- // You'd better actually have a lock, or I will find you and I
- // will hunt you down.
- }
-
- shunique_lock(mutex_type& m, acquire_shared_t, std::adopt_lock_t)
- : m(&m), o(ownership::shared) {
- }
-
- template<typename AcquireType, typename Clock, typename Duration>
- shunique_lock(mutex_type& m, AcquireType at,
- const std::chrono::time_point<Clock, Duration>& t)
- : m(&m), o(ownership::none) {
- try_lock_until(at, t);
- }
-
- template<typename AcquireType, typename Rep, typename Period>
- shunique_lock(mutex_type& m, AcquireType at,
- const std::chrono::duration<Rep, Period>& dur)
- : m(&m), o(ownership::none) {
- try_lock_for(at, dur);
- }
-
- ~shunique_lock() {
- switch (o) {
- case ownership::none:
- return;
- break;
- case ownership::unique:
- m->unlock();
- break;
- case ownership::shared:
- m->unlock_shared();
- break;
- }
- }
-
- shunique_lock(shunique_lock const&) = delete;
- shunique_lock& operator=(shunique_lock const&) = delete;
-
- shunique_lock(shunique_lock&& l) noexcept : shunique_lock() {
- swap(l);
- }
-
- shunique_lock(unique_lock_type&& l) noexcept {
- if (l.owns_lock())
- o = ownership::unique;
- else
- o = ownership::none;
- m = l.release();
- }
-
- shunique_lock(shared_lock_type&& l) noexcept {
- if (l.owns_lock())
- o = ownership::shared;
- else
- o = ownership::none;
- m = l.release();
- }
-
- shunique_lock& operator=(shunique_lock&& l) noexcept {
- shunique_lock(std::move(l)).swap(*this);
- return *this;
- }
-
- shunique_lock& operator=(unique_lock_type&& l) noexcept {
- shunique_lock(std::move(l)).swap(*this);
- return *this;
- }
-
- shunique_lock& operator=(shared_lock_type&& l) noexcept {
- shunique_lock(std::move(l)).swap(*this);
- return *this;
- }
-
- void lock() {
- lockable();
- m->lock();
- o = ownership::unique;
- }
-
- void lock_shared() {
- lockable();
- m->lock_shared();
- o = ownership::shared;
- }
-
- void lock(ceph::acquire_unique_t) {
- lock();
- }
-
- void lock(ceph::acquire_shared_t) {
- lock_shared();
- }
-
- bool try_lock() {
- lockable();
- if (m->try_lock()) {
- o = ownership::unique;
- return true;
- }
- return false;
- }
-
- bool try_lock_shared() {
- lockable();
- if (m->try_lock_shared()) {
- o = ownership::shared;
- return true;
- }
- return false;
- }
-
- bool try_lock(ceph::acquire_unique_t) {
- return try_lock();
- }
-
- bool try_lock(ceph::acquire_shared_t) {
- return try_lock_shared();
- }
-
- template<typename Rep, typename Period>
- bool try_lock_for(const std::chrono::duration<Rep, Period>& dur) {
- lockable();
- if (m->try_lock_for(dur)) {
- o = ownership::unique;
- return true;
- }
- return false;
- }
-
- template<typename Rep, typename Period>
- bool try_lock_shared_for(const std::chrono::duration<Rep, Period>& dur) {
- lockable();
- if (m->try_lock_shared_for(dur)) {
- o = ownership::shared;
- return true;
- }
- return false;
- }
-
- template<typename Rep, typename Period>
- bool try_lock_for(ceph::acquire_unique_t,
- const std::chrono::duration<Rep, Period>& dur) {
- return try_lock_for(dur);
- }
-
- template<typename Rep, typename Period>
- bool try_lock_for(ceph::acquire_shared_t,
- const std::chrono::duration<Rep, Period>& dur) {
- return try_lock_shared_for(dur);
- }
-
- template<typename Clock, typename Duration>
- bool try_lock_until(const std::chrono::time_point<Clock, Duration>& time) {
- lockable();
- if (m->try_lock_until(time)) {
- o = ownership::unique;
- return true;
- }
- return false;
- }
-
- template<typename Clock, typename Duration>
- bool try_lock_shared_until(const std::chrono::time_point<Clock,
- Duration>& time) {
- lockable();
- if (m->try_lock_shared_until(time)) {
- o = ownership::shared;
- return true;
- }
- return false;
- }
-
- template<typename Clock, typename Duration>
- bool try_lock_until(ceph::acquire_unique_t,
- const std::chrono::time_point<Clock, Duration>& time) {
- return try_lock_until(time);
- }
-
- template<typename Clock, typename Duration>
- bool try_lock_until(ceph::acquire_shared_t,
- const std::chrono::time_point<Clock, Duration>& time) {
- return try_lock_shared_until(time);
- }
-
- // Only have a single unlock method. Otherwise we'd be building an
- // Acme lock class suitable only for ravenous coyotes desparate to
- // devour a road runner. It would be bad. It would be disgusting. It
- // would be infelicitous as heck. It would leave our developers in a
- // state of seeming safety unaware of the yawning chasm of failure
- // that had opened beneath their feet that would soon transition
- // into a sickening realization of the error they made and a brief
- // moment of blinking self pity before their program hurled itself
- // into undefined behaviour and plummeted up the stack with core
- // dumps trailing behind it.
-
- void unlock() {
- switch (o) {
- case ownership::none:
- throw std::system_error((int)std::errc::resource_deadlock_would_occur,
- std::generic_category());
- break;
-
- case ownership::unique:
- m->unlock();
- break;
-
- case ownership::shared:
- m->unlock_shared();
- break;
- }
- o = ownership::none;
- }
-
- // Setters
-
- void swap(shunique_lock& u) noexcept {
- std::swap(m, u.m);
- std::swap(o, u.o);
- }
-
- mutex_type* release() noexcept {
- o = ownership::none;
- mutex_type* tm = m;
- m = nullptr;
- return tm;
- }
-
- // Ideally I'd rather make a move constructor for std::unique_lock
- // that took a shunique_lock, but obviously I can't.
- unique_lock_type release_to_unique() {
- if (o == ownership::unique) {
- o = ownership::none;
- unique_lock_type tu(*m, std::adopt_lock);
- m = nullptr;
- return tu;
- } else if (o == ownership::none) {
- unique_lock_type tu(*m, std::defer_lock);
- m = nullptr;
- return tu;
- } else if (m == nullptr) {
- return unique_lock_type();
- }
- throw std::system_error((int)std::errc::operation_not_permitted,
- std::generic_category());
- return unique_lock_type();
- }
-
- shared_lock_type release_to_shared() {
- if (o == ownership::shared) {
- o = ownership::none;
- shared_lock_type ts(*m, std::adopt_lock);
- m = nullptr;
- return ts;
- } else if (o == ownership::none) {
- shared_lock_type ts(*m, std::defer_lock);
- m = nullptr;
- return ts;
- } else if (m == nullptr) {
- return shared_lock_type();
- }
- throw std::system_error((int)std::errc::operation_not_permitted,
- std::generic_category());
- return shared_lock_type();
- }
-
- // Getters
-
- // Note that this returns true if the lock UNIQUE, it will return
- // false for shared
- bool owns_lock() const noexcept {
- return o == ownership::unique;
- }
-
- bool owns_lock_shared() const noexcept {
- return o == ownership::shared;
- }
-
- // If you want to make sure you have a lock of some sort on the
- // mutex, just treat as a bool.
- explicit operator bool() const noexcept {
- return o != ownership::none;
- }
-
- mutex_type* mutex() const noexcept {
- return m;
- }
-
-private:
- void lockable() const {
- if (m == nullptr)
- throw std::system_error((int)std::errc::operation_not_permitted,
- std::generic_category());
- if (o != ownership::none)
- throw std::system_error((int)std::errc::resource_deadlock_would_occur,
- std::generic_category());
- }
-
- mutex_type* m;
- enum struct ownership : uint8_t {
- none, unique, shared
- };
- ownership o;
-};
-} // namespace ceph
-
-namespace std {
- template<typename Mutex>
- void swap(ceph::shunique_lock<Mutex> sh1,
- ceph::shunique_lock<Mutex> sha) {
- sh1.swap(sha);
- }
-} // namespace std
-
-#endif // CEPH_COMMON_SHUNIQUE_LOCK_H
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