w32pthreads: always use Vista+ API, drop XP support

This removes the XP compatibility code, and switches entirely to SWR
locks, which are available starting at Windows Vista.

This removes CRITICAL_SECTION use, which allows us to add
PTHREAD_MUTEX_INITIALIZER, which will be useful later.

Windows XP is hereby not a supported build target anymore. It was
decided in a project vote that this is OK.

7 files changed, 19 insertions, 278 deletions

diff --git a/Changelog b/Changelog
index f44cec679f..2ebdf00ff1 100644
--- a/Changelog
+++ b/Changelog
@@ -28,6 +28,8 @@ version <next>:
 - nsp demuxer
 - support LibreSSL (via libtls)
 - AVX-512/ZMM support added
+- Dropped support for building for Windows XP. The minimum supported Windows
+  version is Windows Vista.
 
 
 version 3.4:
diff --git a/compat/w32pthreads.h b/compat/w32pthreads.h
index eeead6051f..237cab5677 100644
--- a/compat/w32pthreads.h
+++ b/compat/w32pthreads.h
@@ -56,19 +56,12 @@ typedef struct pthread_t {
     void *ret;
 } pthread_t;
 
-/* the conditional variable api for windows 6.0+ uses critical sections and
- * not mutexes */
-typedef CRITICAL_SECTION pthread_mutex_t;
-
-/* This is the CONDITION_VARIABLE typedef for using Windows' native
- * conditional variables on kernels 6.0+. */
-#if HAVE_CONDITION_VARIABLE_PTR
+/* use light weight mutex/condition variable API for Windows Vista and later */
+typedef SRWLOCK pthread_mutex_t;
 typedef CONDITION_VARIABLE pthread_cond_t;
-#else
-typedef struct pthread_cond_t {
-    void *Ptr;
-} pthread_cond_t;
-#endif
+
+#define PTHREAD_MUTEX_INITIALIZER SRWLOCK_INIT
+#define PTHREAD_COND_INITIALIZER CONDITION_VARIABLE_INIT
 
 #if _WIN32_WINNT >= 0x0600
 #define InitializeCriticalSection(x) InitializeCriticalSectionEx(x, 0, 0)
@@ -114,26 +107,25 @@ static av_unused int pthread_join(pthread_t thread, void **value_ptr)
 
 static inline int pthread_mutex_init(pthread_mutex_t *m, void* attr)
 {
-    InitializeCriticalSection(m);
+    InitializeSRWLock(m);
     return 0;
 }
 static inline int pthread_mutex_destroy(pthread_mutex_t *m)
 {
-    DeleteCriticalSection(m);
+    /* Unlocked SWR locks use no resources */
     return 0;
 }
 static inline int pthread_mutex_lock(pthread_mutex_t *m)
 {
-    EnterCriticalSection(m);
+    AcquireSRWLockExclusive(m);
     return 0;
 }
 static inline int pthread_mutex_unlock(pthread_mutex_t *m)
 {
-    LeaveCriticalSection(m);
+    ReleaseSRWLockExclusive(m);
     return 0;
 }
 
-#if _WIN32_WINNT >= 0x0600
 typedef INIT_ONCE pthread_once_t;
 #define PTHREAD_ONCE_INIT INIT_ONCE_STATIC_INIT
 
@@ -167,7 +159,7 @@ static inline int pthread_cond_broadcast(pthread_cond_t *cond)
 
 static inline int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
 {
-    SleepConditionVariableCS(cond, mutex, INFINITE);
+    SleepConditionVariableSRW(cond, mutex, INFINITE, 0);
     return 0;
 }
 
@@ -177,242 +169,4 @@ static inline int pthread_cond_signal(pthread_cond_t *cond)
     return 0;
 }
 
-#else // _WIN32_WINNT < 0x0600
-
-/* atomic init state of dynamically loaded functions */
-static LONG w32thread_init_state = 0;
-static av_unused void w32thread_init(void);
-
-/* for pre-Windows 6.0 platforms, define INIT_ONCE struct,
- * compatible to the one used in the native API */
-
-typedef union pthread_once_t  {
-    void * Ptr;    ///< For the Windows 6.0+ native functions
-    LONG state;    ///< For the pre-Windows 6.0 compat code
-} pthread_once_t;
-
-#define PTHREAD_ONCE_INIT {0}
-
-/* function pointers to init once API on windows 6.0+ kernels */
-static BOOL (WINAPI *initonce_begin)(pthread_once_t *lpInitOnce, DWORD dwFlags, BOOL *fPending, void **lpContext);
-static BOOL (WINAPI *initonce_complete)(pthread_once_t *lpInitOnce, DWORD dwFlags, void *lpContext);
-
-/* pre-Windows 6.0 compat using a spin-lock */
-static inline void w32thread_once_fallback(LONG volatile *state, void (*init_routine)(void))
-{
-    switch (InterlockedCompareExchange(state, 1, 0)) {
-    /* Initial run */
-    case 0:
-        init_routine();
-        InterlockedExchange(state, 2);
-        break;
-    /* Another thread is running init */
-    case 1:
-        while (1) {
-            MemoryBarrier();
-            if (*state == 2)
-                break;
-            Sleep(0);
-        }
-        break;
-    /* Initialization complete */
-    case 2:
-        break;
-    }
-}
-
-static av_unused int pthread_once(pthread_once_t *once_control, void (*init_routine)(void))
-{
-    w32thread_once_fallback(&w32thread_init_state, w32thread_init);
-
-    /* Use native functions on Windows 6.0+ */
-    if (initonce_begin && initonce_complete) {
-        BOOL pending = FALSE;
-        initonce_begin(once_control, 0, &pending, NULL);
-        if (pending)
-            init_routine();
-        initonce_complete(once_control, 0, NULL);
-        return 0;
-    }
-
-    w32thread_once_fallback(&once_control->state, init_routine);
-    return 0;
-}
-
-/* for pre-Windows 6.0 platforms we need to define and use our own condition
- * variable and api */
-
-typedef struct  win32_cond_t {
-    pthread_mutex_t mtx_broadcast;
-    pthread_mutex_t mtx_waiter_count;
-    volatile int waiter_count;
-    HANDLE semaphore;
-    HANDLE waiters_done;
-    volatile int is_broadcast;
-} win32_cond_t;
-
-/* function pointers to conditional variable API on windows 6.0+ kernels */
-static void (WINAPI *cond_broadcast)(pthread_cond_t *cond);
-static void (WINAPI *cond_init)(pthread_cond_t *cond);
-static void (WINAPI *cond_signal)(pthread_cond_t *cond);
-static BOOL (WINAPI *cond_wait)(pthread_cond_t *cond, pthread_mutex_t *mutex,
-                                DWORD milliseconds);
-
-static av_unused int pthread_cond_init(pthread_cond_t *cond, const void *unused_attr)
-{
-    win32_cond_t *win32_cond = NULL;
-
-    w32thread_once_fallback(&w32thread_init_state, w32thread_init);
-
-    if (cond_init) {
-        cond_init(cond);
-        return 0;
-    }
-
-    /* non native condition variables */
-    win32_cond = (win32_cond_t*)av_mallocz(sizeof(win32_cond_t));
-    if (!win32_cond)
-        return ENOMEM;
-    cond->Ptr = win32_cond;
-    win32_cond->semaphore = CreateSemaphore(NULL, 0, 0x7fffffff, NULL);
-    if (!win32_cond->semaphore)
-        return ENOMEM;
-    win32_cond->waiters_done = CreateEvent(NULL, TRUE, FALSE, NULL);
-    if (!win32_cond->waiters_done)
-        return ENOMEM;
-
-    pthread_mutex_init(&win32_cond->mtx_waiter_count, NULL);
-    pthread_mutex_init(&win32_cond->mtx_broadcast, NULL);
-    return 0;
-}
-
-static av_unused int pthread_cond_destroy(pthread_cond_t *cond)
-{
-    win32_cond_t *win32_cond = (win32_cond_t*)cond->Ptr;
-    /* native condition variables do not destroy */
-    if (cond_init)
-        return 0;
-
-    /* non native condition variables */
-    CloseHandle(win32_cond->semaphore);
-    CloseHandle(win32_cond->waiters_done);
-    pthread_mutex_destroy(&win32_cond->mtx_waiter_count);
-    pthread_mutex_destroy(&win32_cond->mtx_broadcast);
-    av_freep(&win32_cond);
-    cond->Ptr = NULL;
-    return 0;
-}
-
-static av_unused int pthread_cond_broadcast(pthread_cond_t *cond)
-{
-    win32_cond_t *win32_cond = (win32_cond_t*)cond->Ptr;
-    int have_waiter;
-
-    if (cond_broadcast) {
-        cond_broadcast(cond);
-        return 0;
-    }
-
-    /* non native condition variables */
-    pthread_mutex_lock(&win32_cond->mtx_broadcast);
-    pthread_mutex_lock(&win32_cond->mtx_waiter_count);
-    have_waiter = 0;
-
-    if (win32_cond->waiter_count) {
-        win32_cond->is_broadcast = 1;
-        have_waiter = 1;
-    }
-
-    if (have_waiter) {
-        ReleaseSemaphore(win32_cond->semaphore, win32_cond->waiter_count, NULL);
-        pthread_mutex_unlock(&win32_cond->mtx_waiter_count);
-        WaitForSingleObject(win32_cond->waiters_done, INFINITE);
-        ResetEvent(win32_cond->waiters_done);
-        win32_cond->is_broadcast = 0;
-    } else
-        pthread_mutex_unlock(&win32_cond->mtx_waiter_count);
-    pthread_mutex_unlock(&win32_cond->mtx_broadcast);
-    return 0;
-}
-
-static av_unused int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
-{
-    win32_cond_t *win32_cond = (win32_cond_t*)cond->Ptr;
-    int last_waiter;
-    if (cond_wait) {
-        cond_wait(cond, mutex, INFINITE);
-        return 0;
-    }
-
-    /* non native condition variables */
-    pthread_mutex_lock(&win32_cond->mtx_broadcast);
-    pthread_mutex_lock(&win32_cond->mtx_waiter_count);
-    win32_cond->waiter_count++;
-    pthread_mutex_unlock(&win32_cond->mtx_waiter_count);
-    pthread_mutex_unlock(&win32_cond->mtx_broadcast);
-
-    // unlock the external mutex
-    pthread_mutex_unlock(mutex);
-    WaitForSingleObject(win32_cond->semaphore, INFINITE);
-
-    pthread_mutex_lock(&win32_cond->mtx_waiter_count);
-    win32_cond->waiter_count--;
-    last_waiter = !win32_cond->waiter_count || !win32_cond->is_broadcast;
-    pthread_mutex_unlock(&win32_cond->mtx_waiter_count);
-
-    if (last_waiter)
-        SetEvent(win32_cond->waiters_done);
-
-    // lock the external mutex
-    return pthread_mutex_lock(mutex);
-}
-
-static av_unused int pthread_cond_signal(pthread_cond_t *cond)
-{
-    win32_cond_t *win32_cond = (win32_cond_t*)cond->Ptr;
-    int have_waiter;
-    if (cond_signal) {
-        cond_signal(cond);
-        return 0;
-    }
-
-    pthread_mutex_lock(&win32_cond->mtx_broadcast);
-
-    /* non-native condition variables */
-    pthread_mutex_lock(&win32_cond->mtx_waiter_count);
-    have_waiter = win32_cond->waiter_count;
-    pthread_mutex_unlock(&win32_cond->mtx_waiter_count);
-
-    if (have_waiter) {
-        ReleaseSemaphore(win32_cond->semaphore, 1, NULL);
-        WaitForSingleObject(win32_cond->waiters_done, INFINITE);
-        ResetEvent(win32_cond->waiters_done);
-    }
-
-    pthread_mutex_unlock(&win32_cond->mtx_broadcast);
-    return 0;
-}
-#endif
-
-static av_unused void w32thread_init(void)
-{
-#if _WIN32_WINNT < 0x0600
-    HMODULE kernel_dll = GetModuleHandle(TEXT("kernel32.dll"));
-    /* if one is available, then they should all be available */
-    cond_init      = (void (WINAPI*)(pthread_cond_t *))
-        GetProcAddress(kernel_dll, "InitializeConditionVariable");
-    cond_broadcast = (void (WINAPI*)(pthread_cond_t *))
-        GetProcAddress(kernel_dll, "WakeAllConditionVariable");
-    cond_signal    = (void (WINAPI*)(pthread_cond_t *))
-        GetProcAddress(kernel_dll, "WakeConditionVariable");
-    cond_wait      = (BOOL (WINAPI*)(pthread_cond_t *, pthread_mutex_t *, DWORD))
-        GetProcAddress(kernel_dll, "SleepConditionVariableCS");
-    initonce_begin = (BOOL (WINAPI*)(pthread_once_t *, DWORD, BOOL *, void **))
-        GetProcAddress(kernel_dll, "InitOnceBeginInitialize");
-    initonce_complete = (BOOL (WINAPI*)(pthread_once_t *, DWORD, void *))
-        GetProcAddress(kernel_dll, "InitOnceComplete");
-#endif
-
-}
-
 #endif /* COMPAT_W32PTHREADS_H */
diff --git a/configure b/configure
index d3187d71ed..19a0f310cf 100755
--- a/configure
+++ b/configure
@@ -2092,7 +2092,6 @@ TOOLCHAIN_FEATURES="
 "
 
 TYPES_LIST="
-    CONDITION_VARIABLE_Ptr
     kCMVideoCodecType_HEVC
     socklen_t
     struct_addrinfo
@@ -5159,6 +5158,8 @@ probe_libc(){
         add_${pfx}cppflags -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
         eval test \$${pfx_no_}cc_type = "gcc" &&
             add_${pfx}cppflags -D__printf__=__gnu_printf__
+        check_${pfx}cpp_condition windows.h "!defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0600" &&
+            add_${pfx}cppflags -D_WIN32_WINNT=0x0600
     elif check_${pfx}cpp_condition _mingw.h "defined __MINGW_VERSION"  ||
          check_${pfx}cpp_condition _mingw.h "defined __MINGW32_VERSION"; then
         eval ${pfx}libc_type=mingw32
@@ -5168,8 +5169,8 @@ probe_libc(){
         add_${pfx}cppflags -U__STRICT_ANSI__ -D__USE_MINGW_ANSI_STDIO=1
         check_${pfx}cpp_condition _mingw.h "__MSVCRT_VERSION__ < 0x0700" &&
             add_${pfx}cppflags -D__MSVCRT_VERSION__=0x0700
-        check_${pfx}cpp_condition windows.h "defined(_WIN32_WINNT) && _WIN32_WINNT < 0x0502" &&
-            add_${pfx}cppflags -D_WIN32_WINNT=0x0502
+        check_${pfx}cpp_condition windows.h "!defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0600" &&
+            add_${pfx}cppflags -D_WIN32_WINNT=0x0600
         eval test \$${pfx_no_}cc_type = "gcc" &&
             add_${pfx}cppflags -D__printf__=__gnu_printf__
     elif check_${pfx}cpp_condition crtversion.h "defined _VC_CRT_MAJOR_VERSION"; then
@@ -5189,14 +5190,14 @@ probe_libc(){
         # 0x601 by default unless something else is set by the user.
         # This can easily lead to us detecting functions only present
         # in such new versions and producing binaries requiring windows 7.0.
-        # Therefore explicitly set the default to XP unless the user has
+        # Therefore explicitly set the default to Vista unless the user has
         # set something else on the command line.
         # Don't do this if WINAPI_FAMILY is set and is set to a non-desktop
         # family. For these cases, configure is free to use any functions
         # found in the SDK headers by default. (Alternatively, we could force
         # _WIN32_WINNT to 0x0602 in that case.)
         check_${pfx}cpp_condition stdlib.h "defined(_WIN32_WINNT)" ||
-            { check_${pfx}cpp <<EOF && add_${pfx}cppflags -D_WIN32_WINNT=0x0502; }
+            { check_${pfx}cpp <<EOF && add_${pfx}cppflags -D_WIN32_WINNT=0x0600; }
 #ifdef WINAPI_FAMILY
 #include <winapifamily.h>
 #if !WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
@@ -5674,7 +5675,6 @@ check_func_headers windows.h SetConsoleTextAttribute
 check_func_headers windows.h SetConsoleCtrlHandler
 check_func_headers windows.h Sleep
 check_func_headers windows.h VirtualAlloc
-check_struct windows.h "CONDITION_VARIABLE" Ptr
 check_func_headers glob.h glob
 enabled xlib &&
     check_func_headers "X11/Xlib.h X11/extensions/Xvlib.h" XvGetPortAttribute -lXv -lX11 -lXext
@@ -5758,6 +5758,7 @@ check_cpp_condition windows.h "!WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP
 
 if ! disabled w32threads && ! enabled pthreads; then
     check_func_headers "windows.h process.h" _beginthreadex &&
+        check_type "windows.h" CONDITION_VARIABLE &&
         enable w32threads || disable w32threads
     if ! enabled w32threads && enabled winrt; then
         check_func_headers "windows.h" CreateThread &&
diff --git a/libavcodec/pthread_frame.c b/libavcodec/pthread_frame.c
index e6e6d1f599..25aa3e2cd2 100644
--- a/libavcodec/pthread_frame.c
+++ b/libavcodec/pthread_frame.c
@@ -728,10 +728,6 @@ int ff_frame_thread_init(AVCodecContext *avctx)
     FrameThreadContext *fctx;
     int i, err = 0;
 
-#if HAVE_W32THREADS
-    w32thread_init();
-#endif
-
     if (!thread_count) {
         int nb_cpus = av_cpu_count();
 #if FF_API_DEBUG_MV
diff --git a/libavcodec/pthread_slice.c b/libavcodec/pthread_slice.c
index d659f9b0ba..77cfe3c9f6 100644
--- a/libavcodec/pthread_slice.c
+++ b/libavcodec/pthread_slice.c
@@ -132,10 +132,6 @@ int ff_slice_thread_init(AVCodecContext *avctx)
     int thread_count = avctx->thread_count;
     static void (*mainfunc)(void *);
 
-#if HAVE_W32THREADS
-    w32thread_init();
-#endif
-
     // We cannot do this in the encoder init as the threads are created before
     if (av_codec_is_encoder(avctx->codec) &&
         avctx->codec_id == AV_CODEC_ID_MPEG1VIDEO &&
diff --git a/libavfilter/pthread.c b/libavfilter/pthread.c
index 567dd4c178..7e37c73ca3 100644
--- a/libavfilter/pthread.c
+++ b/libavfilter/pthread.c
@@ -85,10 +85,6 @@ int ff_graph_thread_init(AVFilterGraph *graph)
 {
     int ret;
 
-#if HAVE_W32THREADS
-    w32thread_init();
-#endif
-
     if (graph->nb_threads == 1) {
         graph->thread_type = 0;
         return 0;
diff --git a/libavutil/slicethread.c b/libavutil/slicethread.c
index c43f87a2aa..dfbe551ef2 100644
--- a/libavutil/slicethread.c
+++ b/libavutil/slicethread.c
@@ -99,10 +99,6 @@ int avpriv_slicethread_create(AVSliceThread **pctx, void *priv,
     AVSliceThread *ctx;
     int nb_workers, i;
 
-#if HAVE_W32THREADS
-    w32thread_init();
-#endif
-
     av_assert0(nb_threads >= 0);
     if (!nb_threads) {
         int nb_cpus = av_cpu_count();