rwlock: Added SDL_rwlock API for shared locks.

src/thread/generic/SDL_sysmutex.c

@@ -159,3 +159,4 @@ int SDL_UnlockMutex(SDL_mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doe
     return 0;
 #endif /* SDL_THREADS_DISABLED */
 }
+

src/thread/generic/SDL_sysrwlock.c

@@ -0,0 +1,185 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+/* An implementation of rwlocks using mutexes, condition variables, and atomics. */
+
+#include "SDL_systhread_c.h"
+
+#include "../generic/SDL_sysrwlock_c.h"
+
+/* If two implementations are to be compiled into SDL (the active one
+ * will be chosen at runtime), the function names need to be
+ * suffixed
+ */
+/* !!! FIXME: this is quite a tapdance with macros and the build system, maybe we can simplify how we do this. --ryan. */
+#ifndef SDL_THREAD_GENERIC_RWLOCK_SUFFIX
+#define SDL_CreateRWLock_generic SDL_CreateRWLock
+#define SDL_DestroyRWLock_generic SDL_DestroyRWLock
+#define SDL_LockRWLockForReading_generic SDL_LockRWLockForReading
+#define SDL_LockRWLockForWriting_generic SDL_LockRWLockForWriting
+#define SDL_TryLockRWLockForReading_generic SDL_TryLockRWLockForReading
+#define SDL_TryLockRWLockForWriting_generic SDL_TryLockRWLockForWriting
+#define SDL_UnlockRWLock_generic SDL_UnlockRWLock
+#endif
+
+struct SDL_rwlock
+{
+    SDL_mutex *lock;
+    SDL_cond *condition;
+    SDL_threadID writer_thread;
+    SDL_AtomicInt reader_count;
+    SDL_AtomicInt writer_count;
+};
+
+SDL_rwlock *SDL_CreateRWLock_generic(void)
+{
+    SDL_rwlock *rwlock = (SDL_rwlock *) SDL_malloc(sizeof (*rwlock));
+
+    if (!rwlock) {
+        SDL_OutOfMemory();
+        return NULL;
+    }
+
+    rwlock->lock = SDL_CreateMutex();
+    if (!rwlock->lock) {
+        SDL_free(rwlock);
+        return NULL;
+    }
+
+    rwlock->condition = SDL_CreateCond();
+    if (!rwlock->condition) {
+        SDL_DestroyMutex(rwlock->lock);
+        SDL_free(rwlock);
+        return NULL;
+    }
+
+    SDL_AtomicSet(&rwlock->reader_count, 0);
+    SDL_AtomicSet(&rwlock->writer_count, 0);
+
+    return rwlock;
+}
+
+void SDL_DestroyRWLock_generic(SDL_rwlock *rwlock)
+{
+    if (rwlock) {
+        SDL_DestroyMutex(rwlock->lock);
+        SDL_DestroyCond(rwlock->condition);
+        SDL_free(rwlock);
+    }
+}
+
+int SDL_LockRWLockForReading_generic(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    } else if (SDL_LockMutex(rwlock->lock) == -1) {
+        return -1;
+    }
+
+    SDL_assert(SDL_AtomicGet(&rwlock->writer_count) == 0);  /* shouldn't be able to grab lock if there's a writer! */
+
+    SDL_AtomicAdd(&rwlock->reader_count, 1);
+    SDL_UnlockMutex(rwlock->lock);   /* other readers can attempt to share the lock. */
+    return 0;
+}
+
+int SDL_LockRWLockForWriting_generic(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    } else if (SDL_LockMutex(rwlock->lock) == -1) {
+        return -1;
+    }
+
+    while (SDL_AtomicGet(&rwlock->reader_count) > 0) {  /* while something is holding the shared lock, keep waiting. */
+        SDL_CondWait(rwlock->condition, rwlock->lock);  /* release the lock and wait for readers holding the shared lock to release it, regrab the lock. */
+    }
+
+    /* we hold the lock! */
+    SDL_AtomicAdd(&rwlock->writer_count, 1);  /* we let these be recursive, but the API doesn't require this. It _does_ trust you unlock correctly! */
+
+    return 0;
+}
+
+int SDL_TryLockRWLockForReading_generic(SDL_rwlock *rwlock)
+{
+    int rc;
+
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    }
+
+    rc = SDL_TryLockMutex(rwlock->lock);
+    if (rc != 0) {
+        /* !!! FIXME: there is a small window where a reader has to lock the mutex, and if we hit that, we will return SDL_RWLOCK_TIMEDOUT even though we could have shared the lock. */
+        return rc;
+    }
+
+    SDL_assert(SDL_AtomicGet(&rwlock->writer_count) == 0);  /* shouldn't be able to grab lock if there's a writer! */
+
+    SDL_AtomicAdd(&rwlock->reader_count, 1);
+    SDL_UnlockMutex(rwlock->lock);   /* other readers can attempt to share the lock. */
+    return 0;
+}
+
+int SDL_TryLockRWLockForWriting_generic(SDL_rwlock *rwlock)
+{
+    int rc;
+
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    } else if ((rc = SDL_TryLockMutex(rwlock->lock)) != 0) {
+        return rc;
+    }
+
+    if (SDL_AtomicGet(&rwlock->reader_count) > 0) {  /* a reader is using the shared lock, treat it as unavailable. */
+        SDL_UnlockMutex(rwlock->lock);
+        return SDL_RWLOCK_TIMEDOUT;
+    }
+
+    /* we hold the lock! */
+    SDL_AtomicAdd(&rwlock->writer_count, 1);  /* we let these be recursive, but the API doesn't require this. It _does_ trust you unlock correctly! */
+
+    return 0;
+}
+
+int SDL_UnlockRWLock_generic(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    }
+
+    SDL_LockMutex(rwlock->lock);  /* recursive lock for writers, readers grab lock to make sure things are sane. */
+
+    if (SDL_AtomicGet(&rwlock->reader_count) > 0) {  /* we're a reader */
+        SDL_AtomicAdd(&rwlock->reader_count, -1);
+        SDL_CondBroadcast(rwlock->condition);  /* alert any pending writers to attempt to try to grab the lock again. */
+    } else if (SDL_AtomicGet(&rwlock->writer_count) > 0) {  /* we're a writer */
+        SDL_AtomicAdd(&rwlock->writer_count, -1);
+        SDL_UnlockMutex(rwlock->lock);  /* recursive unlock. */
+    }
+
+    SDL_UnlockMutex(rwlock->lock);
+
+    return 0;
+}
+

src/thread/generic/SDL_sysrwlock_c.h

@@ -0,0 +1,38 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+#ifndef SDL_sysrwlock_c_h_
+#define SDL_sysrwlock_c_h_
+
+#ifdef SDL_THREAD_GENERIC_RWLOCK_SUFFIX
+
+SDL_rwlock *SDL_CreateRWLock_generic(void);
+void SDL_DestroyRWLock_generic(SDL_rwlock *rwlock);
+int SDL_LockRWLockForReading_generic(SDL_rwlock *rwlock);
+int SDL_LockRWLockForWriting_generic(SDL_rwlock *rwlock);
+int SDL_TryLockRWLockForReading_generic(SDL_rwlock *rwlock);
+int SDL_TryLockRWLockForWriting_generic(SDL_rwlock *rwlock);
+int SDL_UnlockRWLock_generic(SDL_rwlock *rwlock);
+
+#endif /* SDL_THREAD_GENERIC_RWLOCK_SUFFIX */
+
+#endif /* SDL_sysrwlock_c_h_ */

src/thread/ngage/SDL_sysmutex.cpp

@@ -109,3 +109,4 @@ int SDL_UnlockMutex(SDL_mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doe
 
     return 0;
 }
+

src/thread/ngage/SDL_syssem.cpp

@@ -24,6 +24,7 @@
 
 #include <e32std.h>
 
+/* !!! FIXME: Should this be SDL_MUTEX_TIMEDOUT? */
 #define SDL_MUTEX_TIMEOUT -2
 
 struct SDL_semaphore

src/thread/pthread/SDL_sysmutex.c

@@ -23,20 +23,7 @@
 #include <errno.h>
 #include <pthread.h>
 
-
-#if !(defined(SDL_THREAD_PTHREAD_RECURSIVE_MUTEX) || \
-    defined(SDL_THREAD_PTHREAD_RECURSIVE_MUTEX_NP))
-#define FAKE_RECURSIVE_MUTEX
-#endif
-
-struct SDL_mutex
-{
-    pthread_mutex_t id;
-#ifdef FAKE_RECURSIVE_MUTEX
-    int recursive;
-    pthread_t owner;
-#endif
-};
+#include "SDL_sysmutex_c.h"
 
 SDL_mutex *
 SDL_CreateMutex(void)
@@ -186,3 +173,4 @@ int SDL_UnlockMutex(SDL_mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doe
 
     return 0;
 }
+

src/thread/pthread/SDL_sysmutex_c.h

@@ -23,9 +23,18 @@
 #ifndef SDL_mutex_c_h_
 #define SDL_mutex_c_h_
 
+#if !(defined(SDL_THREAD_PTHREAD_RECURSIVE_MUTEX) || \
+    defined(SDL_THREAD_PTHREAD_RECURSIVE_MUTEX_NP))
+#define FAKE_RECURSIVE_MUTEX
+#endif
+
 struct SDL_mutex
 {
     pthread_mutex_t id;
+#ifdef FAKE_RECURSIVE_MUTEX
+    int recursive;
+    pthread_t owner;
+#endif
 };
 
 #endif /* SDL_mutex_c_h_ */

src/thread/pthread/SDL_sysrwlock.c

@@ -0,0 +1,127 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+#include <errno.h>
+#include <pthread.h>
+
+struct SDL_rwlock
+{
+    pthread_rwlock_t id;
+};
+
+
+SDL_rwlock *
+SDL_CreateRWLock(void)
+{
+    SDL_rwlock *rwlock;
+
+    /* Allocate the structure */
+    rwlock = (SDL_rwlock *)SDL_calloc(1, sizeof(*rwlock));
+    if (rwlock) {
+        if (pthread_rwlock_init(&rwlock->id, NULL) != 0) {
+            SDL_SetError("pthread_rwlock_init() failed");
+            SDL_free(rwlock);
+            rwlock = NULL;
+        }
+    } else {
+        SDL_OutOfMemory();
+    }
+    return rwlock;
+}
+
+void SDL_DestroyRWLock(SDL_rwlock *rwlock)
+{
+    if (rwlock) {
+        pthread_rwlock_destroy(&rwlock->id);
+        SDL_free(rwlock);
+    }
+}
+
+int SDL_LockRWLockForReading(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (rwlock == NULL) {
+        return SDL_InvalidParamError("rwlock");
+    } else if (pthread_rwlock_rdlock(&rwlock->id) != 0) {
+        return SDL_SetError("pthread_rwlock_rdlock() failed");
+    }
+    return 0;
+}
+
+int SDL_LockRWLockForWriting(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (rwlock == NULL) {
+        return SDL_InvalidParamError("rwlock");
+    } else if (pthread_rwlock_wrlock(&rwlock->id) != 0) {
+        return SDL_SetError("pthread_rwlock_wrlock() failed");
+    }
+    return 0;
+}
+
+int SDL_TryLockRWLockForReading(SDL_rwlock *rwlock)
+{
+    int retval = 0;
+
+    if (rwlock == NULL) {
+        retval = SDL_InvalidParamError("rwlock");
+    } else {
+        const int result = pthread_rwlock_tryrdlock(&rwlock->id);
+        if (result != 0) {
+            if (result == EBUSY) {
+                retval = SDL_RWLOCK_TIMEDOUT;
+            } else {
+                retval = SDL_SetError("pthread_rwlock_tryrdlock() failed");
+            }
+        }
+    }
+    return retval;
+}
+
+int SDL_TryLockRWLockForWriting(SDL_rwlock *rwlock)
+{
+    int retval = 0;
+
+    if (rwlock == NULL) {
+        retval = SDL_InvalidParamError("rwlock");
+    } else {
+        const int result = pthread_rwlock_trywrlock(&rwlock->id);
+        if (result != 0) {
+            if (result == EBUSY) {
+                retval = SDL_RWLOCK_TIMEDOUT;
+            } else {
+                retval = SDL_SetError("pthread_rwlock_tryrdlock() failed");
+            }
+        }
+    }
+
+    return retval;
+}
+
+int SDL_UnlockRWLock(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (rwlock == NULL) {
+        return SDL_InvalidParamError("rwlock");
+    } else if (pthread_rwlock_unlock(&rwlock->id) != 0) {
+        return SDL_SetError("pthread_rwlock_unlock() failed");
+    }
+    return 0;
+}
+

src/thread/stdcpp/SDL_sysmutex.cpp

@@ -97,3 +97,4 @@ SDL_UnlockMutex(SDL_mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't
     mutex->cpp_mutex.unlock();
     return 0;
 }
+

src/thread/stdcpp/SDL_sysmutex_c.h

@@ -26,3 +26,4 @@ struct SDL_mutex
 {
     std::recursive_mutex cpp_mutex;
 };
+

src/thread/stdcpp/SDL_sysrwlock.cpp

@@ -0,0 +1,130 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+#include <shared_mutex>
+#include <system_error>
+#include <Windows.h>
+
+struct SDL_rwlock
+{
+    std::shared_mutex cpp_mutex;
+    SDL_threadID write_owner;
+};
+
+/* Create a rwlock */
+extern "C" SDL_rwlock *SDL_CreateRWLock(void)
+{
+    /* Allocate and initialize the rwlock */
+    try {
+        SDL_rwlock *rwlock = new SDL_rwlock;
+        return rwlock;
+    } catch (std::system_error &ex) {
+        SDL_SetError("unable to create a C++ rwlock: code=%d; %s", ex.code(), ex.what());
+        return NULL;
+    } catch (std::bad_alloc &) {
+        SDL_OutOfMemory();
+        return NULL;
+    }
+}
+
+/* Free the rwlock */
+extern "C" void SDL_DestroyRWLock(SDL_rwlock *rwlock)
+{
+    if (rwlock != NULL) {
+        delete rwlock;
+    }
+}
+
+/* Lock the rwlock */
+extern "C" int SDL_LockRWLockForReading(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    }
+
+    try {
+        rwlock->cpp_mutex.lock_shared();
+        return 0;
+    } catch (std::system_error &ex) {
+        return SDL_SetError("unable to lock a C++ rwlock: code=%d; %s", ex.code(), ex.what());
+    }
+}
+
+/* Lock the rwlock for writing */
+extern "C" int SDL_LockRWLockForWriting(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    }
+
+    try {
+        rwlock->cpp_mutex.lock();
+        rwlock->write_owner = SDL_ThreadID();
+        return 0;
+    } catch (std::system_error &ex) {
+        return SDL_SetError("unable to lock a C++ rwlock: code=%d; %s", ex.code(), ex.what());
+    }
+}
+
+/* TryLock the rwlock for reading */
+int SDL_TryLockRWLockForReading(SDL_rwlock *rwlock)
+{
+    int retval = 0;
+
+    if (!rwlock) {
+        retval = SDL_InvalidParamError("rwlock");
+    } else if (rwlock->cpp_mutex.try_lock_shared() == false) {
+        retval = SDL_RWLOCK_TIMEDOUT;
+    }
+    return retval;
+}
+
+/* TryLock the rwlock for writing */
+int SDL_TryLockRWLockForWriting(SDL_rwlock *rwlock)
+{
+    int retval = 0;
+
+    if (!rwlock) {
+        retval = SDL_InvalidParamError("rwlock");
+    } else if (rwlock->cpp_mutex.try_lock() == false) {
+        retval = SDL_RWLOCK_TIMEDOUT;
+    } else {
+        rwlock->write_owner = SDL_ThreadID();
+    }
+    return retval;
+}
+
+/* Unlock the rwlock */
+extern "C" int
+SDL_UnlockRWLock(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    if (!rwlock) {
+        return SDL_InvalidParamError("rwlock");
+    } else if (rwlock->write_owner == SDL_ThreadID()) {
+        rwlock->write_owner = 0;
+        rwlock->cpp_mutex.unlock();
+    } else {
+        rwlock->cpp_mutex.unlock_shared();
+    }
+    return 0;
+}
+

src/thread/windows/SDL_sysrwlock_srw.c

@@ -0,0 +1,258 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+/**
+ * Implementation based on Slim Reader/Writer (SRW) Locks for Win 7 and newer.
+ */
+
+/* This header makes sure SRWLOCK is actually declared, even on ancient WinSDKs. */
+#include "SDL_sysmutex_c.h"
+
+typedef VOID(WINAPI *pfnInitializeSRWLock)(PSRWLOCK);
+typedef VOID(WINAPI *pfnReleaseSRWLockShared)(PSRWLOCK);
+typedef VOID(WINAPI *pfnAcquireSRWLockShared)(PSRWLOCK);
+typedef BOOLEAN(WINAPI *pfnTryAcquireSRWLockShared)(PSRWLOCK);
+typedef VOID(WINAPI *pfnReleaseSRWLockExclusive)(PSRWLOCK);
+typedef VOID(WINAPI *pfnAcquireSRWLockExclusive)(PSRWLOCK);
+typedef BOOLEAN(WINAPI *pfnTryAcquireSRWLockExclusive)(PSRWLOCK);
+
+#ifdef __WINRT__
+/* Functions are guaranteed to be available */
+#define pTryAcquireSRWLockExclusive TryAcquireSRWLockExclusive
+#define pInitializeSRWLock InitializeSRWLock
+#define pReleaseSRWLockShared ReleaseSRWLockShared
+#define pAcquireSRWLockShared AcquireSRWLockShared
+#define pTryAcquireSRWLockShared TryAcquireSRWLockShared
+#define pReleaseSRWLockExclusive ReleaseSRWLockExclusive
+#define pAcquireSRWLockExclusive AcquireSRWLockExclusive
+#define pTryAcquireSRWLockExclusive TryAcquireSRWLockExclusive
+#else
+static pfnInitializeSRWLock pInitializeSRWLock = NULL;
+static pfnReleaseSRWLockShared pReleaseSRWLockShared = NULL;
+static pfnAcquireSRWLockShared pAcquireSRWLockShared = NULL;
+static pfnTryAcquireSRWLockShared  pTryAcquireSRWLockShared = NULL;
+static pfnReleaseSRWLockExclusive pReleaseSRWLockExclusive = NULL;
+static pfnAcquireSRWLockExclusive pAcquireSRWLockExclusive = NULL;
+static pfnTryAcquireSRWLockExclusive pTryAcquireSRWLockExclusive = NULL;
+#endif
+
+typedef SDL_rwlock *(*pfnSDL_CreateRWLock)(void);
+typedef void (*pfnSDL_DestroyRWLock)(SDL_rwlock *);
+typedef int (*pfnSDL_LockRWLockForReading)(SDL_rwlock *);
+typedef int (*pfnSDL_LockRWLockForWriting)(SDL_rwlock *);
+typedef int (*pfnSDL_TryLockRWLockForReading)(SDL_rwlock *);
+typedef int (*pfnSDL_TryLockRWLockForWriting)(SDL_rwlock *);
+typedef int (*pfnSDL_UnlockRWLock)(SDL_rwlock *);
+
+typedef struct SDL_rwlock_impl_t
+{
+    pfnSDL_CreateRWLock Create;
+    pfnSDL_DestroyRWLock Destroy;
+    pfnSDL_LockRWLockForReading LockForReading;
+    pfnSDL_LockRWLockForWriting LockForWriting;
+    pfnSDL_TryLockRWLockForReading TryLockForReading;
+    pfnSDL_TryLockRWLockForWriting TryLockForWriting;
+    pfnSDL_UnlockRWLock Unlock;
+} SDL_rwlock_impl_t;
+
+/* Implementation will be chosen at runtime based on available Kernel features */
+static SDL_rwlock_impl_t SDL_rwlock_impl_active = { 0 };
+
+/* rwlock implementation using Win7+ slim read/write locks (SRWLOCK) */
+
+typedef struct SDL_rwlock_srw
+{
+    SRWLOCK srw;
+    SDL_threadID write_owner;
+} SDL_rwlock_srw;
+
+static SDL_rwlock *SDL_CreateRWLock_srw(void)
+{
+    SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *)SDL_calloc(1, sizeof(*rwlock));
+    if (rwlock == NULL) {
+        SDL_OutOfMemory();
+    }
+    pInitializeSRWLock(&rwlock->srw);
+    return (SDL_rwlock *)rwlock;
+}
+
+static void SDL_DestroyRWLock_srw(SDL_rwlock *_rwlock)
+{
+    SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
+    if (rwlock) {
+        /* There are no kernel allocated resources */
+        SDL_free(rwlock);
+    }
+}
+
+static int SDL_LockRWLockForReading_srw(SDL_rwlock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
+    if (rwlock == NULL) {
+        return SDL_InvalidParamError("rwlock");
+    }
+    pAcquireSRWLockShared(&rwlock->srw);
+    return 0;
+}
+
+static int SDL_LockRWLockForWriting_srw(SDL_rwlock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
+    if (rwlock == NULL) {
+        return SDL_InvalidParamError("rwlock");
+    }
+    pAcquireSRWLockExclusive(&rwlock->srw);
+    rwlock->write_owner = SDL_ThreadID();
+    return 0;
+}
+
+static int SDL_TryLockRWLockForReading_srw(SDL_rwlock *_rwlock)
+{
+    SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
+    int retval = 0;
+
+    if (rwlock == NULL) {
+        retval = SDL_InvalidParamError("rwlock");
+    } else {
+        retval = pTryAcquireSRWLockShared(&rwlock->srw) ? 0 : SDL_RWLOCK_TIMEDOUT;
+    }
+    return retval;
+}
+
+static int SDL_TryLockRWLockForWriting_srw(SDL_rwlock *_rwlock)
+{
+    SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
+    int retval = 0;
+
+    if (rwlock == NULL) {
+        retval = SDL_InvalidParamError("rwlock");
+    } else {
+        retval = pTryAcquireSRWLockExclusive(&rwlock->srw) ? 0 : SDL_RWLOCK_TIMEDOUT;
+    }
+    return retval;
+}
+
+static int SDL_UnlockRWLock_srw(SDL_rwlock *_rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    SDL_rwlock_srw *rwlock = (SDL_rwlock_srw *) _rwlock;
+    if (rwlock == NULL) {
+        return SDL_InvalidParamError("rwlock");
+    } else if (rwlock->write_owner == SDL_ThreadID()) {
+        rwlock->write_owner = 0;
+        pReleaseSRWLockExclusive(&rwlock->srw);
+    } else {
+        pReleaseSRWLockShared(&rwlock->srw);
+    }
+    return 0;
+}
+
+static const SDL_rwlock_impl_t SDL_rwlock_impl_srw = {
+    &SDL_CreateRWLock_srw,
+    &SDL_DestroyRWLock_srw,
+    &SDL_LockRWLockForReading_srw,
+    &SDL_LockRWLockForWriting_srw,
+    &SDL_TryLockRWLockForReading_srw,
+    &SDL_TryLockRWLockForWriting_srw,
+    &SDL_UnlockRWLock_srw
+};
+
+#ifndef __WINRT__
+
+#include "../generic/SDL_sysrwlock_c.h"
+
+/* Generic rwlock implementation using SDL_mutex, SDL_cond, and SDL_AtomicInt */
+static const SDL_rwlock_impl_t SDL_rwlock_impl_generic = {
+    &SDL_CreateRWLock_generic,
+    &SDL_DestroyRWLock_generic,
+    &SDL_LockRWLockForReading_generic,
+    &SDL_LockRWLockForWriting_generic,
+    &SDL_TryLockRWLockForReading_generic,
+    &SDL_TryLockRWLockForWriting_generic,
+    &SDL_UnlockRWLock_generic
+};
+#endif
+
+SDL_rwlock *SDL_CreateRWLock(void)
+{
+    if (SDL_rwlock_impl_active.Create == NULL) {
+        const SDL_rwlock_impl_t *impl;
+
+#ifdef __WINRT__
+        /* Link statically on this platform */
+        impl = &SDL_rwlock_impl_srw;
+#else
+        /* Default to generic implementation, works with all mutex implementations */
+        impl = &SDL_rwlock_impl_generic;
+        {
+            HMODULE kernel32 = GetModuleHandle(TEXT("kernel32.dll"));
+            if (kernel32) {
+                SDL_bool okay = SDL_TRUE;
+                #define LOOKUP_SRW_SYM(sym) if (okay) { if ((p##sym = (pfn##sym)GetProcAddress(kernel32, #sym)) == NULL) { okay = SDL_FALSE; } }
+                LOOKUP_SRW_SYM(InitializeSRWLock);
+                LOOKUP_SRW_SYM(ReleaseSRWLockShared);
+                LOOKUP_SRW_SYM(AcquireSRWLockShared);
+                LOOKUP_SRW_SYM(TryAcquireSRWLockShared);
+                LOOKUP_SRW_SYM(ReleaseSRWLockExclusive);
+                LOOKUP_SRW_SYM(AcquireSRWLockExclusive);
+                LOOKUP_SRW_SYM(TryAcquireSRWLockExclusive);
+                #undef LOOKUP_SRW_SYM
+                if (okay) {
+                    impl = &SDL_rwlock_impl_srw;  /* Use the Windows provided API instead of generic fallback */
+                }
+            }
+        }
+#endif
+
+        SDL_copyp(&SDL_rwlock_impl_active, impl);
+    }
+    return SDL_rwlock_impl_active.Create();
+}
+
+void SDL_DestroyRWLock(SDL_rwlock *rwlock)
+{
+    SDL_rwlock_impl_active.Destroy(rwlock);
+}
+
+int SDL_LockRWLockForReading(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    return SDL_rwlock_impl_active.LockForReading(rwlock);
+}
+
+int SDL_LockRWLockForWriting(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    return SDL_rwlock_impl_active.LockForWriting(rwlock);
+}
+
+int SDL_TryLockRWLockForReading(SDL_rwlock *rwlock)
+{
+    return SDL_rwlock_impl_active.TryLockForReading(rwlock);
+}
+
+int SDL_TryLockRWLockForWriting(SDL_rwlock *rwlock)
+{
+    return SDL_rwlock_impl_active.TryLockForWriting(rwlock);
+}
+
+int SDL_UnlockRWLock(SDL_rwlock *rwlock) SDL_NO_THREAD_SAFETY_ANALYSIS /* clang doesn't know about NULL mutexes */
+{
+    return SDL_rwlock_impl_active.Unlock(rwlock);
+}