A src/third-party/discord-rpc/include/mingw-std-threads/shared_mutex

@@ -0,0 +1,497 @@
+/// \file mingw.shared_mutex.h
+/// \brief Standard-compliant shared_mutex for MinGW
+///
+/// (c) 2017 by Nathaniel J. McClatchey, Athens OH, United States
+/// \author Nathaniel J. McClatchey
+///
+/// \copyright Simplified (2-clause) BSD License.
+///
+/// \note This file may become part of the mingw-w64 runtime package. If/when
+/// this happens, the appropriate license will be added, i.e. this code will
+/// become dual-licensed, and the current BSD 2-clause license will stay.
+/// \note Target Windows version is determined by WINVER, which is determined in
+/// <windows.h> from _WIN32_WINNT, which can itself be set by the user.
+
+//  Notes on the namespaces:
+//  - The implementation can be accessed directly in the namespace
+//    mingw_stdthread.
+//  - Objects will be brought into namespace std by a using directive. This
+//    will cause objects declared in std (such as MinGW's implementation) to
+//    hide this implementation's definitions.
+//  - To avoid poluting the namespace with implementation details, all objects
+//    to be pushed into std will be placed in mingw_stdthread::visible.
+//  The end result is that if MinGW supplies an object, it is automatically
+//  used. If MinGW does not supply an object, this implementation's version will
+//  instead be used.
+
+#ifndef MINGW_SHARED_MUTEX_H_
+#define MINGW_SHARED_MUTEX_H_
+
+#if !defined(__cplusplus) || (__cplusplus < 201103L)
+#error A C++11 compiler is required!
+#endif
+
+#include <cassert>
+//  For descriptive errors.
+#include <system_error>
+//    Implementing a shared_mutex without OS support will require atomic read-
+//  modify-write capacity.
+#include <atomic>
+//  For timing in shared_lock and shared_timed_mutex.
+#include <chrono>
+#include <limits>
+
+//    Use MinGW's shared_lock class template, if it's available. Requires C++14.
+//  If unavailable (eg. because this library is being used in C++11), then an
+//  implementation of shared_lock is provided by this header.
+#if (__cplusplus >= 201402L)
+#include_next <shared_mutex>
+#endif
+
+//  For defer_lock_t, adopt_lock_t, and try_to_lock_t
+#include <mutex>
+//  For this_thread::yield.
+#include <thread>
+
+//  Might be able to use native Slim Reader-Writer (SRW) locks.
+#ifdef _WIN32
+#include <windows.h>
+#endif
+
+namespace mingw_stdthread
+{
+//  Define a portable atomics-based shared_mutex
+namespace portable
+{
+class shared_mutex
+{
+    typedef uint_fast16_t counter_type;
+    std::atomic<counter_type> mCounter {0};
+    static constexpr counter_type kWriteBit = 1 << (std::numeric_limits<counter_type>::digits - 1);
+
+#if STDMUTEX_RECURSION_CHECKS
+//  Runtime checker for verifying owner threads. Note: Exclusive mode only.
+    _OwnerThread mOwnerThread {};
+#endif
+public:
+    typedef shared_mutex * native_handle_type;
+
+    shared_mutex () = default;
+
+//  No form of copying or moving should be allowed.
+    shared_mutex (const shared_mutex&) = delete;
+    shared_mutex & operator= (const shared_mutex&) = delete;
+
+    ~shared_mutex ()
+    {
+//  Terminate if someone tries to destroy an owned mutex.
+        assert(mCounter.load(std::memory_order_relaxed) == 0);
+    }
+
+    void lock_shared (void)
+    {
+        counter_type expected = mCounter.load(std::memory_order_relaxed);
+        do
+        {
+//  Delay if writing or if too many readers are attempting to read.
+            if (expected >= kWriteBit - 1)
+            {
+                using namespace std;
+                using namespace this_thread;
+                yield();
+                expected = mCounter.load(std::memory_order_relaxed);
+                continue;
+            }
+            if (mCounter.compare_exchange_weak(expected,
+                                               static_cast<counter_type>(expected + 1),
+                                               std::memory_order_acquire,
+                                               std::memory_order_relaxed))
+                break;
+        }
+        while (true);
+    }
+
+    bool try_lock_shared (void)
+    {
+        counter_type expected = mCounter.load(std::memory_order_relaxed) & static_cast<counter_type>(~kWriteBit);
+        if (expected + 1 == kWriteBit)
+            return false;
+        else
+            return mCounter.compare_exchange_strong( expected,
+                                                    static_cast<counter_type>(expected + 1),
+                                                    std::memory_order_acquire,
+                                                    std::memory_order_relaxed);
+    }
+
+    void unlock_shared (void)
+    {
+        using namespace std;
+#ifndef NDEBUG
+        if (!(mCounter.fetch_sub(1, memory_order_release) & static_cast<counter_type>(~kWriteBit)))
+            throw system_error(make_error_code(errc::operation_not_permitted));
+#else
+        mCounter.fetch_sub(1, memory_order_release);
+#endif
+    }
+
+//  Behavior is undefined if a lock was previously acquired.
+    void lock (void)
+    {
+#if STDMUTEX_RECURSION_CHECKS
+        DWORD self = mOwnerThread.checkOwnerBeforeLock();
+#endif
+        using namespace std;
+//  Might be able to use relaxed memory order...
+//  Wait for the write-lock to be unlocked, then claim the write slot.
+        counter_type current;
+        while ((current = mCounter.fetch_or(kWriteBit, std::memory_order_acquire)) & kWriteBit)
+            this_thread::yield();
+//  Wait for readers to finish up.
+        while (current != kWriteBit)
+        {
+            this_thread::yield();
+            current = mCounter.load(std::memory_order_acquire);
+        }
+#if STDMUTEX_RECURSION_CHECKS
+        mOwnerThread.setOwnerAfterLock(self);
+#endif
+    }
+
+    bool try_lock (void)
+    {
+#if STDMUTEX_RECURSION_CHECKS
+        DWORD self = mOwnerThread.checkOwnerBeforeLock();
+#endif
+        counter_type expected = 0;
+        bool ret = mCounter.compare_exchange_strong(expected, kWriteBit,
+                                                    std::memory_order_acquire,
+                                                    std::memory_order_relaxed);
+#if STDMUTEX_RECURSION_CHECKS
+        if (ret)
+            mOwnerThread.setOwnerAfterLock(self);
+#endif
+        return ret;
+    }
+
+    void unlock (void)
+    {
+#if STDMUTEX_RECURSION_CHECKS
+        mOwnerThread.checkSetOwnerBeforeUnlock();
+#endif
+        using namespace std;
+#ifndef NDEBUG
+        if (mCounter.load(memory_order_relaxed) != kWriteBit)
+            throw system_error(make_error_code(errc::operation_not_permitted));
+#endif
+        mCounter.store(0, memory_order_release);
+    }
+
+    native_handle_type native_handle (void)
+    {
+        return this;
+    }
+};
+
+} //  Namespace portable
+
+//    The native shared_mutex implementation primarily uses features of Windows
+//  Vista, but the features used for try_lock and try_lock_shared were not
+//  introduced until Windows 7. To allow limited use while compiling for Vista,
+//  I define the class without try_* functions in that case.
+//    Only fully-featured implementations will be placed into namespace std.
+#if defined(_WIN32) && (WINVER >= _WIN32_WINNT_VISTA)
+namespace vista
+{
+class condition_variable_any;
+}
+
+namespace windows7
+{
+//  We already #include "mingw.mutex.h". May as well reduce redundancy.
+class shared_mutex : windows7::mutex
+{
+//    Allow condition_variable_any (and only condition_variable_any) to treat a
+//  shared_mutex as its base class.
+    friend class vista::condition_variable_any;
+public:
+    using windows7::mutex::native_handle_type;
+    using windows7::mutex::lock;
+    using windows7::mutex::unlock;
+    using windows7::mutex::native_handle;
+
+    void lock_shared (void)
+    {
+        AcquireSRWLockShared(native_handle());
+    }
+
+    void unlock_shared (void)
+    {
+        ReleaseSRWLockShared(native_handle());
+    }
+
+//  TryAcquireSRW functions are a Windows 7 feature.
+#if (WINVER >= _WIN32_WINNT_WIN7)
+    bool try_lock_shared (void)
+    {
+        return TryAcquireSRWLockShared(native_handle()) != 0;
+    }
+
+    using windows7::mutex::try_lock;
+#endif
+};
+
+} //  Namespace windows7
+#endif  //  Compiling for Vista
+#if (defined(_WIN32) && (WINVER >= _WIN32_WINNT_WIN7))
+using windows7::shared_mutex;
+#else
+using portable::shared_mutex;
+#endif
+
+class shared_timed_mutex : shared_mutex
+{
+    typedef shared_mutex Base;
+public:
+    using Base::lock;
+    using Base::try_lock;
+    using Base::unlock;
+    using Base::lock_shared;
+    using Base::try_lock_shared;
+    using Base::unlock_shared;
+
+    template< class Clock, class Duration >
+    bool try_lock_until ( const std::chrono::time_point<Clock,Duration>& cutoff )
+    {
+        do
+        {
+            if (try_lock())
+                return true;
+        }
+        while (std::chrono::steady_clock::now() < cutoff);
+        return false;
+    }
+
+    template< class Rep, class Period >
+    bool try_lock_for (const std::chrono::duration<Rep,Period>& rel_time)
+    {
+        return try_lock_until(std::chrono::steady_clock::now() + rel_time);
+    }
+
+    template< class Clock, class Duration >
+    bool try_lock_shared_until ( const std::chrono::time_point<Clock,Duration>& cutoff )
+    {
+        do
+        {
+            if (try_lock_shared())
+                return true;
+        }
+        while (std::chrono::steady_clock::now() < cutoff);
+        return false;
+    }
+
+    template< class Rep, class Period >
+    bool try_lock_shared_for (const std::chrono::duration<Rep,Period>& rel_time)
+    {
+        return try_lock_shared_until(std::chrono::steady_clock::now() + rel_time);
+    }
+};
+
+#if __cplusplus >= 201402L
+using std::shared_lock;
+#else
+//    If not supplied by shared_mutex (eg. because C++14 is not supported), I
+//  supply the various helper classes that the header should have defined.
+template<class Mutex>
+class shared_lock
+{
+    Mutex * mMutex;
+    bool mOwns;
+//  Reduce code redundancy
+    void verify_lockable (void)
+    {
+        using namespace std;
+        if (mMutex == nullptr)
+            throw system_error(make_error_code(errc::operation_not_permitted));
+        if (mOwns)
+            throw system_error(make_error_code(errc::resource_deadlock_would_occur));
+    }
+public:
+    typedef Mutex mutex_type;
+
+    shared_lock (void) noexcept
+        : mMutex(nullptr), mOwns(false)
+    {
+    }
+
+    shared_lock (shared_lock<Mutex> && other) noexcept
+        : mMutex(other.mutex_), mOwns(other.owns_)
+    {
+        other.mMutex = nullptr;
+        other.mOwns = false;
+    }
+
+    explicit shared_lock (mutex_type & m)
+        : mMutex(&m), mOwns(true)
+    {
+        mMutex->lock_shared();
+    }
+
+    shared_lock (mutex_type & m, defer_lock_t) noexcept
+        : mMutex(&m), mOwns(false)
+    {
+    }
+
+    shared_lock (mutex_type & m, adopt_lock_t)
+        : mMutex(&m), mOwns(true)
+    {
+    }
+
+    shared_lock (mutex_type & m, try_to_lock_t)
+        : mMutex(&m), mOwns(m.try_lock_shared())
+    {
+    }
+
+    template< class Rep, class Period >
+    shared_lock( mutex_type& m, const std::chrono::duration<Rep,Period>& timeout_duration )
+        : mMutex(&m), mOwns(m.try_lock_shared_for(timeout_duration))
+    {
+    }
+
+    template< class Clock, class Duration >
+    shared_lock( mutex_type& m, const std::chrono::time_point<Clock,Duration>& timeout_time )
+        : mMutex(&m), mOwns(m.try_lock_shared_until(timeout_time))
+    {
+    }
+
+    shared_lock& operator= (shared_lock<Mutex> && other) noexcept
+    {
+        if (&other != this)
+        {
+            if (mOwns)
+                mMutex->unlock_shared();
+            mMutex = other.mMutex;
+            mOwns = other.mOwns;
+            other.mMutex = nullptr;
+            other.mOwns = false;
+        }
+        return *this;
+    }
+
+
+    ~shared_lock (void)
+    {
+        if (mOwns)
+            mMutex->unlock_shared();
+    }
+
+    shared_lock (const shared_lock<Mutex> &) = delete;
+    shared_lock& operator= (const shared_lock<Mutex> &) = delete;
+
+//  Shared locking
+    void lock (void)
+    {
+        verify_lockable();
+        mMutex->lock_shared();
+        mOwns = true;
+    }
+
+    bool try_lock (void)
+    {
+        verify_lockable();
+        mOwns = mMutex->try_lock_shared();
+        return mOwns;
+    }
+
+    template< class Clock, class Duration >
+    bool try_lock_until( const std::chrono::time_point<Clock,Duration>& cutoff )
+    {
+        verify_lockable();
+        do
+        {
+            mOwns = mMutex->try_lock_shared();
+            if (mOwns)
+                return mOwns;
+        }
+        while (std::chrono::steady_clock::now() < cutoff);
+        return false;
+    }
+
+    template< class Rep, class Period >
+    bool try_lock_for (const std::chrono::duration<Rep,Period>& rel_time)
+    {
+        return try_lock_until(std::chrono::steady_clock::now() + rel_time);
+    }
+
+    void unlock (void)
+    {
+        using namespace std;
+        if (!mOwns)
+            throw system_error(make_error_code(errc::operation_not_permitted));
+        mMutex->unlock_shared();
+        mOwns = false;
+    }
+
+//  Modifiers
+    void swap (shared_lock<Mutex> & other) noexcept
+    {
+        using namespace std;
+        swap(mMutex, other.mMutex);
+        swap(mOwns, other.mOwns);
+    }
+
+    mutex_type * release (void) noexcept
+    {
+        mutex_type * ptr = mMutex;
+        mMutex = nullptr;
+        mOwns = false;
+        return ptr;
+    }
+//  Observers
+    mutex_type * mutex (void) const noexcept
+    {
+        return mMutex;
+    }
+
+    bool owns_lock (void) const noexcept
+    {
+        return mOwns;
+    }
+
+    explicit operator bool () const noexcept
+    {
+        return owns_lock();
+    }
+};
+
+template< class Mutex >
+void swap( shared_lock<Mutex>& lhs, shared_lock<Mutex>& rhs ) noexcept
+{
+    lhs.swap(rhs);
+}
+#endif  //  C++11
+} //  Namespace mingw_stdthread
+
+namespace std
+{
+//    Because of quirks of the compiler, the common "using namespace std;"
+//  directive would flatten the namespaces and introduce ambiguity where there
+//  was none. Direct specification (std::), however, would be unaffected.
+//    Take the safe option, and include only in the presence of MinGW's win32
+//  implementation.
+#if (__cplusplus < 201703L) || (defined(__MINGW32__ ) && !defined(_GLIBCXX_HAS_GTHREADS))
+using mingw_stdthread::shared_mutex;
+#endif
+#if (__cplusplus < 201402L) || (defined(__MINGW32__ ) && !defined(_GLIBCXX_HAS_GTHREADS))
+using mingw_stdthread::shared_timed_mutex;
+using mingw_stdthread::shared_lock;
+#elif !defined(MINGW_STDTHREAD_REDUNDANCY_WARNING)  //  Skip repetition
+#define MINGW_STDTHREAD_REDUNDANCY_WARNING
+#pragma message "This version of MinGW seems to include a win32 port of\
+ pthreads, and probably already has C++ std threading classes implemented,\
+ based on pthreads. These classes, found in namespace std, are not overridden\
+ by the mingw-std-thread library. If you would still like to use this\
+ implementation (as it is more lightweight), use the classes provided in\
+ namespace mingw_stdthread."
+#endif
+} //  Namespace std
+#endif // MINGW_SHARED_MUTEX_H_