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(int refAmount) {
+#ifdef SK_DEBUG
+    SkASSERT(2 == refAmount || 3 == refAmount);
+    if (3 == refAmount) {
+        // assert that we are not already attached (i.e. the low-bit is 0)
+        SkASSERT(0 == (fRefCnt & 1));
+    }
+#endif
+
+    const int32_t new_count = sk_atomic_add(&fRefCnt, refAmount) + refAmount;
+    const int owners = new_count >> 1;
+    const int in_cache = new_count & 1;
+
+    SkASSERT(owners >= 2);
+
+    if (2 == owners) {

[qiankun, 2014/09/25 07:15:11]

In some cases, owners may exceed 2 before SkCachedData is attached. Is it
correct for such case?

+        sk_membar_acquire__after_atomic_dec();
+        if (in_cache) {
+            this->lock();
+        }
+    }
+}
+
+void SkCachedData::internalUnref(int refAmount) {
+#ifdef SK_DEBUG
+    SkASSERT(2 == refAmount || 3 == refAmount);
+    if (3 == refAmount) {
+        // assert that we are already attached (i.e. the low-bit is 1)
+        SkASSERT(1 == (fRefCnt & 1));
+    }
+#endif
+
+    const int32_t new_count = sk_atomic_add(&fRefCnt, -refAmount) - refAmount;
+    const int owners = new_count >> 1;
+    const int in_cache = new_count & 1;
+
+    switch (owners) {
+        case 0:
+            sk_membar_acquire__after_atomic_dec();
+            SkDELETE(this);
+            break;
+        case 1:
+            sk_membar_acquire__after_atomic_dec();
+            if (in_cache) {
+                this->unlock();
+            }
+            break;
+        default:
+            break;
+    }
+}
+
+void SkCachedData::lock() {
+    switch (fStorageType) {
+        case kMalloc_StorageType:
+            fData = fStorage.fMalloc;
+            break;
+        case kDiscardableMemory_StorageType:
+            if (fStorage.fDM->lock()) {
+                fData = fStorage.fDM->data();
+            } else {
+                fData = NULL;   // signal failure to lock, contents are gone
+            }
+            break;
+    }
+}
+
+void SkCachedData::unlock() {
+    switch (fStorageType) {
+        case kMalloc_StorageType:
+            // nothing to do/check
+            break;
+        case kDiscardableMemory_StorageType:
+            if (fData) {    // did the previous lock succeed?
+                fStorage.fDM->unlock();
+            }
+            break;
+    }
+    fData = NULL;   // signal that we're in an unlocked state
+}
+