Make mutex semaphore based.

include/core/SkMutex.h

Index: include/core/SkMutex.h
diff --git a/include/core/SkMutex.h b/include/core/SkMutex.h
index eb5e29b80a7e1c0ad06ec8d4f292711aeae08599..77a00f02354074ab6b6635ffaba4d3b48746401d 100644
--- a/include/core/SkMutex.h
+++ b/include/core/SkMutex.h
@@ -9,15 +9,73 @@
 #define SkMutex_DEFINED
 
 // This file is not part of the public Skia API.
+#include "../private/SkSemaphore.h"
 #include "SkTypes.h"
 
-// IWYU pragma: begin_exports
-#if defined(SK_BUILD_FOR_WIN)
-    #include "../ports/SkMutex_win.h"
+#define SK_MUTEX_SEMAPHORE_INIT {1, {0}}
+
+#ifdef SK_DEBUG
+    #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT, 0}
 #else
-    #include "../ports/SkMutex_pthread.h"
+    #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT}
+#endif
+
+// Using POD-style initialization prevents the generation of a static initializer.
+//
+// Without magic statics there are no thread safety guarantees on initialization
+// of local statics (even POD). As a result, it is illegal to use
+// SK_DECLARE_STATIC_MUTEX in a function.
+//
+// Because SkBaseMutex is not a primitive, a static SkBaseMutex cannot be
+// initialized in a class with this macro.
+#define SK_DECLARE_STATIC_MUTEX(name) namespace {} static SkBaseMutex name = SK_BASE_MUTEX_INIT;
+
+// TODO(herb): unify this with the ThreadID in SkSharedMutex.cpp.
+#ifdef SK_DEBUG
+    #ifdef SK_BUILD_FOR_WIN
+        #include <windows.h>
+        inline int64_t sk_get_thread_id() { return GetCurrentThreadId(); }
+    #else
+        #include <pthread.h>
+        inline int64_t sk_get_thread_id() { return (int64_t)pthread_self(); }
+    #endif
 #endif
-// IWYU pragma: end_exports
+
+typedef int64_t SkThreadID;
+
+SkDEBUGCODE(static const SkThreadID kNoOwner = 0;)
+
+struct SkBaseMutex {
+    void acquire() {
+        fSemaphore.wait();
+        SkDEBUGCODE(fOwner = sk_get_thread_id();)
+    }
+
+    void release() {
+        this->assertHeld();
+        SkDEBUGCODE(fOwner = kNoOwner;)
+        fSemaphore.signal();
+    }
+
+    void assertHeld() {
+        SkASSERT(fOwner == sk_get_thread_id());
+    }
+
+    SkBaseSemaphore fSemaphore;
+    SkDEBUGCODE(SkThreadID fOwner;)
+};
+
+// This needs to use subclassing instead of encapsulation to make SkAutoMutexAcquire to work.
+class SkMutex : public SkBaseMutex {
+public:
+    SkMutex () {
+        fSemaphore = SK_MUTEX_SEMAPHORE_INIT;
+        SkDEBUGCODE(fOwner = kNoOwner);
+    }
+    ~SkMutex () { fSemaphore.deleteSemaphore(); }
+    SkMutex(const SkMutex&) = delete;
+    SkMutex& operator=(const SkMutex&) = delete;
+};
 
 template <typename Lock>
 class SkAutoTAcquire : SkNoncopyable {
@@ -59,8 +117,6 @@ private:
 };
 
 typedef SkAutoTAcquire<SkBaseMutex> SkAutoMutexAcquire;
-
 #define SkAutoMutexAcquire(...) SK_REQUIRE_LOCAL_VAR(SkAutoMutexAcquire)
 
-
 #endif//SkMutex_DEFINED