Add SkCachedData and use it for SkMipMap

src/core/SkCachedData.cpp

+/*
+ * 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_priv.h"
+#include "SkRefCnt.h"
+#include "SkDiscardableMemory.h"
+
+SkCachedData::SkCachedData(void* data, size_t size)
+    : fData(data)
+    , fSize(size)
+    , fRefCnt(2)    // 1 owner, not in cache
+{
+    fStorage.fMalloc = data;
+    fStorageType = kMalloc_StorageType;
+}
+
+SkCachedData::SkCachedData(size_t size, SkDiscardableMemory* dm)
+    : fData(dm->data())
+    , fSize(size)
+    , fRefCnt(2)    // 1 owner, not in cache
+{
+    fStorage.fDM = dm;
+    fStorageType = kDiscardableMemory_StorageType;
+}
+
+SkCachedData::~SkCachedData() {
+    switch (fStorageType) {
+        case kMalloc_StorageType:
+            sk_free(fStorage.fMalloc);
+            break;
+        case kDiscardableMemory_StorageType:
+            SkDELETE(fStorage.fDM);
+            break;
+    }
+}
+
+void SkCachedData::internalRef(bool fromCache) const {
+    SkCachedData* writable = const_cast<SkCachedData*>(this);
+    SkAutoMutexAcquire ama(writable->get_mutex());
+    
+    int32_t amount;
+    if (fromCache) {
+        // assert that we are not already attached (i.e. the low-bit is 0)
+        SkASSERT(0 == (writable->fRefCnt & 1));
+        amount = 3;
+    } else {
+        // from client
+        amount = 2;
+    }
+
+    const int32_t new_count = (writable->fRefCnt += amount);
+    const int new_owners = new_count >> 1;
+    const int in_cache = new_count & 1;
+
+    SkASSERT(new_owners >= 2);
+
+    if (2 == new_owners && !fromCache) {
+        if (in_cache) {
+            writable->in_mutex_lock();
+        }
+    }
+}
+
+bool SkCachedData::doInternalUnref(bool fromCache) const {
+    SkCachedData* writable = const_cast<SkCachedData*>(this);
+    SkAutoMutexAcquire ama(writable->get_mutex());
+
+    int32_t amount;
+    if (fromCache) {
+        // assert that we are already attached (i.e. the low-bit is 1)
+        SkASSERT(1 == (fRefCnt & 1));
+        amount = 3;
+    } else {
+        // from client
+        amount = 2;
+    }
+    
+    const int32_t new_count = (writable->fRefCnt -= amount);
+    const int new_owners = new_count >> 1;
+    const int in_cache = new_count & 1;
+
+    switch (new_owners) {
+        case 0:
+            writable->in_mutex_prepareToDelete();
+            break;
+        case 1:
+            if (in_cache) {
+                // 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.
+                writable->in_mutex_unlock();
+            }
+            break;
+        default:
+            break;
+    }
+    return 0 == new_owners;
+}
+
+void SkCachedData::internalUnref(bool fromCache) const {
+    if (this->doInternalUnref(fromCache)) {
+        // can't delete inside doInternalUnref, since it is locking a mutex (which we own)
+        SkDELETE(this);
+    }
+}
+
+void SkCachedData::in_mutex_lock() {
+    this->assert_in_mutex();
+
+    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::in_mutex_unlock() {
+    this->assert_in_mutex();
+    
+    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
+}
+
+void SkCachedData::in_mutex_prepareToDelete() {
+    this->assert_in_mutex();
+    
+    switch (fStorageType) {
+        case kMalloc_StorageType:
+            // nothing to do/check
+            break;
+        case kDiscardableMemory_StorageType:
+            // discardable request that it be unlocked before being deleted
+            if (fData) {
+                fStorage.fDM->unlock();
+            }
+            break;
+    }
+}
+