Revert of Modernize SkMutex and SkSemaphore.

include/private/SkMutex.h

Index: include/private/SkMutex.h
diff --git a/include/private/SkMutex.h b/include/private/SkMutex.h
index b9af00f8a8be02fc1e3b7794e23d761b1c94c761..8c78e1205c8796261be4b19468338a00af8afdc5 100644
--- a/include/private/SkMutex.h
+++ b/include/private/SkMutex.h
@@ -8,20 +8,33 @@
 #ifndef SkMutex_DEFINED
 #define SkMutex_DEFINED
 
+// This file is not part of the public Skia API.
 #include "../private/SkSemaphore.h"
-#include "../private/SkThreadID.h"
 #include "SkTypes.h"
 
-// TODO: no need for this anymore.
-#define SK_DECLARE_STATIC_MUTEX(name) static SkMutex name;
+#ifdef SK_DEBUG
+    #include "../private/SkThreadID.h"
+#endif
 
-class SkMutex {
-public:
-    constexpr SkMutex() = default;
+#define SK_MUTEX_SEMAPHORE_INIT {1, {0}}
 
-    SkMutex(const SkMutex&)            = delete;
-    SkMutex& operator=(const SkMutex&) = delete;
+#ifdef SK_DEBUG
+    #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT, 0}
+#else
+    #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;
+
+struct SkBaseMutex {
     void acquire() {
         fSemaphore.wait();
         SkDEBUGCODE(fOwner = SkGetThreadID();)
@@ -37,9 +50,20 @@
         SkASSERT(fOwner == SkGetThreadID());
     }
 
-private:
-    SkSemaphore fSemaphore{1};
-    SkDEBUGCODE(SkThreadID fOwner{kIllegalThreadID};)
+    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 = kIllegalThreadID);
+    }
+    ~SkMutex () { fSemaphore.deleteSemaphore(); }
+    SkMutex(const SkMutex&) = delete;
+    SkMutex& operator=(const SkMutex&) = delete;
 };
 
 template <typename Lock>
@@ -92,10 +116,10 @@
     Lock &fLock;
 };
 
-typedef SkAutoTAcquire<SkMutex> SkAutoMutexAcquire;
+typedef SkAutoTAcquire<SkBaseMutex> SkAutoMutexAcquire;
 #define SkAutoMutexAcquire(...) SK_REQUIRE_LOCAL_VAR(SkAutoMutexAcquire)
 
-typedef SkAutoTExclusive<SkMutex> SkAutoMutexExclusive;
+typedef SkAutoTExclusive<SkBaseMutex> SkAutoMutexExclusive;
 #define SkAutoMutexExclusive(...) SK_REQUIRE_LOCAL_VAR(SkAutoMutexExclusive)
 
 #endif//SkMutex_DEFINED