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
+{}
+
+void SkCachedData::ref() {
+    const int32_t count = sk_atomic_add(&fRefCnt, 2) + 2;
+    const int owners = count >> 1;
+    const int in_cache = count & 1;
+
+    SkASSERT(owners >= 2);
+
+    if (2 == owners) {
+        sk_membar_acquire__after_atomic_dec();
+        if (in_cache) {

[mtklein, 2014/09/23 22:16:55]

So, if I add SkASSERT(in_cache) just before each if (in_cache) { ...},
everything seems to run fine.  This makes me think we've got more power encoded
into fRefCnt than we need.

[reed2, 2014/09/24 01:23:57]

Sounds like I need to expand my tests to (try to) exercise the case when we're
not in the cache...

+            this->lock();
+        }
+    }
+}
+
+void SkCachedData::unref() {
+    const int32_t count = sk_atomic_add(&fRefCnt, -2) - 2;
+    const int owners = count >> 1;
+    const int in_cache = 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::ref_from_cache() {
+    SkASSERT(0 == (fRefCnt & 1));
+    sk_atomic_add(&fRefCnt, 3);
+}
+
+void SkCachedData::unref_from_cache() {
+    SkASSERT(1 == (fRefCnt & 1));
+    sk_atomic_add(&fRefCnt, -3);
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+class SkCachedData_Discardable : public SkCachedData {
+public:
+    // we take ownership of dm
+    SkCachedData_Discardable(SkDiscardableMemory* dm, size_t size)
+        : INHERITED(dm->data(), size)
+        , fDM(dm)
+        , fSuccessfulLock(false)
+    {}
+    
+    virtual ~SkCachedData_Discardable() {
+        SkDELETE(fDM);
+    }
+    
+protected:
+    virtual void onLock() SK_OVERRIDE {
+        fSuccessfulLock = fDM->lock();
+        this->setData(fSuccessfulLock ? fDM->data() : NULL);
+    }
+    
+    virtual void onUnlock() SK_OVERRIDE {
+        if (fSuccessfulLock) {
+            fDM->unlock();
+        }
+    }
+    
+private:
+    SkDiscardableMemory*    fDM;
+    bool                    fSuccessfulLock;
+
+    typedef SkCachedData INHERITED;
+};
+
+class SkCachedData_Malloc : public SkCachedData {
+public:
+    // data was allocated via sk_malloc
+    SkCachedData_Malloc(void* data, size_t size) : INHERITED(data, size), fMallocData(data) {}
+    
+    virtual ~SkCachedData_Malloc() {
+        sk_free(fMallocData);
+    }
+    
+    virtual void onLock() SK_OVERRIDE {
+        this->setData(fMallocData);
+    }
+
+    virtual void onUnlock() SK_OVERRIDE {}
+
+private:
+    void* fMallocData;
+
+    typedef SkCachedData INHERITED;
+};
+
+SkCachedData* SkCachedData::Create(size_t size, SkDiscardableMemory* dm) {
+    if (dm) {
+        return SkNEW_ARGS(SkCachedData_Discardable, (dm, size));
+    } else {
+        return SkNEW_ARGS(SkCachedData_Malloc, (sk_malloc_throw(size), size));
+    }
+}
+