[gfm] add thread-safety support for Windows (#34)

CMakeLists.txt

@@ -18,7 +18,7 @@ option(CMARK_TESTS "Build cmark-gfm tests and enable testing" ON)
 option(CMARK_STATIC "Build static libcmark-gfm library" ON)
 option(CMARK_SHARED "Build shared libcmark-gfm library" ON)
 option(CMARK_LIB_FUZZER "Build libFuzzer fuzzing harness" OFF)
-option(CMARK_THREADING "Add locks around static accesses via pthreads" OFF)
+option(CMARK_THREADING "Add locks around static accesses" OFF)
 
 add_subdirectory(src)
 add_subdirectory(extensions)

src/include/mutex.h

@@ -5,6 +5,12 @@
 
 #ifdef CMARK_THREADING
 
+#if __has_include(<unistd.h>)
+#include <unistd.h>
+#endif
+
+#if defined (_POSIX_THREADS)
+
 #include <pthread.h>
 
 #define CMARK_DEFINE_ONCE(NAME) static pthread_once_t NAME##_once = PTHREAD_ONCE_INIT;
@@ -22,6 +28,29 @@ pthread_mutex_lock(&NAME##_lock);
 
 #define CMARK_UNLOCK(NAME) pthread_mutex_unlock(&NAME##_lock);
 
+#elif defined(_WIN32) // building for windows
+
+#define _WIN32_WINNT 0x0600
+#include <synchapi.h>
+
+#define CMARK_DEFINE_ONCE(NAME) static INIT_ONCE NAME##_once = INIT_ONCE_STATIC_INIT;
+
+#define CMARK_RUN_ONCE(NAME, FUNC) do { \
+  BOOL fStatus; BOOL fPending; \
+  fStatus = InitOnceBeginInitialize(&NAME##_once, 0, &fPending, NULL); \
+  if (!fStatus || !fPending) break; \
+  FUNC(); \
+  InitOnceComplete(&NAME##_once, 0, NULL); \
+} while (0);
+
+#define CMARK_DEFINE_LOCK(NAME) static SRWLOCK NAME##_lock = SRWLOCK_INIT;
+
+#define CMARK_INITIALIZE_AND_LOCK(NAME) AcquireSRWLockExclusive(&NAME##_lock);
+
+#define CMARK_UNLOCK(NAME) ReleaseSRWLockExclusive(&NAME##_lock);
+
+#endif
+
 #else // no threading support
 
 static CMARK_INLINE bool check_latch(int *latch) {