--- /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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