Add SkCachedData and use it for SkMipMap

src/core/SkCachedData.cpp

Index: src/core/SkCachedData.cpp
diff --git a/src/core/SkCachedData.cpp b/src/core/SkCachedData.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..93d119820ee203eab440bc359c9fcd8ef0ed473e
--- /dev/null
+++ b/src/core/SkCachedData.cpp
@@ -0,0 +1,175 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCachedData.h"
+#include "SkRefCnt.h"
+#include "SkDiscardableMemory.h"
+
+SkCachedData::SkCachedData(void* data, size_t size)
+    : fData(data)
+    , fSize(size)
+    , fRefCnt(1)
+    , fStorageType(kMalloc_StorageType)
+    , fInCache(false)
+    , fIsLocked(true)
+{
+    fStorage.fMalloc = data;
+}
+
+SkCachedData::SkCachedData(size_t size, SkDiscardableMemory* dm)
+    : fData(dm->data())
+    , fSize(size)
+    , fRefCnt(1)
+    , fStorageType(kDiscardableMemory_StorageType)
+    , fInCache(false)
+    , fIsLocked(true)
+{
+    fStorage.fDM = dm;
+}
+
+SkCachedData::~SkCachedData() {
+    switch (fStorageType) {
+        case kMalloc_StorageType:
+            sk_free(fStorage.fMalloc);
+            break;
+        case kDiscardableMemory_StorageType:
+            SkDELETE(fStorage.fDM);
+            break;
+    }
+}
+
+class SkCachedData::AutoMutexWritable {
+public:
+    AutoMutexWritable(const SkCachedData* cd) : fCD(const_cast<SkCachedData*>(cd)) {
+        fCD->fMutex.acquire();
+        fCD->validate();
+    }
+    ~AutoMutexWritable() {
+        fCD->validate();
+        fCD->fMutex.release();
+    }
+
+    SkCachedData* get() { return fCD; }
+    SkCachedData* operator->() { return fCD; }
+
+private:
+    SkCachedData* fCD;
+};
+
+void SkCachedData::internalRef(bool fromCache) const {
+    AutoMutexWritable(this)->inMutexRef(fromCache);
+}
+
+void SkCachedData::internalUnref(bool fromCache) const {
+    if (AutoMutexWritable(this)->inMutexUnref(fromCache)) {
+        // can't delete inside doInternalUnref, since it is locking a mutex (which we own)
+        SkDELETE(this);
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+void SkCachedData::inMutexRef(bool fromCache) {
+    if ((1 == fRefCnt) && fInCache) {
+        this->inMutexLock();
+    }
+    
+    fRefCnt += 1;
+    if (fromCache) {
+        SkASSERT(!fInCache);
+        fInCache = true;
+    }
+}
+
+bool SkCachedData::inMutexUnref(bool fromCache) {
+    switch (--fRefCnt) {
+        case 0:
+            // we're going to be deleted, so we need to be unlocked (for DiscardableMemory)
+            if (fIsLocked) {
+                this->inMutexUnlock();
+            }
+            break;
+        case 1:
+            if (fInCache && !fromCache) {
+                // If we're down to 1 owner, and that owner is the cache, this it is safe
+                // to unlock (and mutate fData) even if the cache is in a different thread,
+                // as the cache is NOT allowed to inspect or use fData.
+                this->inMutexUnlock();
+            }
+            break;
+        default:
+            break;
+    }
+    
+    if (fromCache) {
+        SkASSERT(fInCache);
+        fInCache = false;
+    }
+    
+    // return true when we need to be deleted
+    return 0 == fRefCnt;
+}
+
+void SkCachedData::inMutexLock() {
+    fMutex.assertHeld();
+    
+    SkASSERT(!fIsLocked);
+    fIsLocked = true;
+    
+    switch (fStorageType) {
+        case kMalloc_StorageType:
+            this->setData(fStorage.fMalloc);
+            break;
+        case kDiscardableMemory_StorageType:
+            if (fStorage.fDM->lock()) {
+                this->setData(fStorage.fDM->data());
+            } else {
+                this->setData(NULL);   // signal failure to lock, contents are gone
+            }
+            break;
+    }
+}
+
+void SkCachedData::inMutexUnlock() {
+    fMutex.assertHeld();
+    
+    SkASSERT(fIsLocked);
+    fIsLocked = false;
+    
+    switch (fStorageType) {
+        case kMalloc_StorageType:
+            // nothing to do/check
+            break;
+        case kDiscardableMemory_StorageType:
+            if (fData) {    // did the previous lock succeed?
+                fStorage.fDM->unlock();
+            }
+            break;
+    }
+    this->setData(NULL);   // signal that we're in an unlocked state
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+#ifdef SK_DEBUG
+void SkCachedData::validate() const {
+    if (fIsLocked) {
+        SkASSERT((fInCache && fRefCnt > 1) || !fInCache);
+        switch (fStorageType) {
+            case kMalloc_StorageType:
+                SkASSERT(fData == fStorage.fMalloc);
+                break;
+            case kDiscardableMemory_StorageType:
+                // fData can be null or the actual value, depending if DM's lock succeeded
+                break;
+        }
+    } else {
+        SkASSERT((fInCache && 1 == fRefCnt) || (0 == fRefCnt));
+        SkASSERT(NULL == fData);
+    }
+}
+#endif