Add GrProgramElement base class for GrEffect with deferred exec ref.

include/gpu/GrProgramElement.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrProgramElement_DEFINED
+#define GrProgramElement_DEFINED
+
+#include "SkRefCnt.h"
+#include "SkTArray.h"
+
+class GrProgramResource;
+
+/**
+ * Base class for GrEffect (and future GrGeometryProcessor). GrDrawState uses this to manage
+ * transitioning a GrEffect from being owned by a client to being scheduled for execution. It
+ * converts resources owned by the effect from being ref'ed to having pending reads/writes.
+ *
+ * All GrGpuResource objects owned by a GrProgramElement or derived classes (either directly or
+ * indirectly) must be wrapped in a GrProgramResource and registered with the GrProgramElement using
+ * addGrProgramResource(). This allows the regular refs to be converted to pending IO events
+ * when the program element is scheduled for deferred execution.
+ */
+class GrProgramElement : public SkNoncopyable {
+public:
+    SK_DECLARE_INST_COUNT_ROOT(GrProgramElement)
+
+    virtual ~GrProgramElement() {
+        // fRefCnt can be one when an effect is created statically using GR_CREATE_STATIC_EFFECT
+        SkASSERT((0 == fRefCnt || 1 == fRefCnt) && 0 == fPendingExecutions);
+        // Set to invalid values.
+        SkDEBUGCODE(fRefCnt = fPendingExecutions = -10;)
+    }
+
+    void ref() const {
+        // Once the ref cnt reaches zero it should never be ref'ed again.
+        SkASSERT(fRefCnt > 0);
+        this->validate();
+        ++fRefCnt;
+    }
+
+    void unref() const {
+        this->validate();
+        --fRefCnt;
+        if (0 == fRefCnt && 0 == fPendingExecutions) {
+            SkDELETE(this);
+        }
+    }
+
+    void validate() const {
+#ifdef SK_DEBUG
+        SkASSERT(fRefCnt >= 0);
+        SkASSERT(fPendingExecutions >= 0);
+        SkASSERT(fRefCnt + fPendingExecutions > 0);
+#endif
+    }
+
+protected:
+    GrProgramElement() : fRefCnt(1), fPendingExecutions(0) {}
+
+    /** Subclasses registers their resources using this function. It is assumed the GrProgramResouce
+        is and will remain owned by the subclass and this function will retain a raw ptr. Once a
+        GrProgramResource is registered its setResource must not be called.
+     */
+    void addProgramResource(const GrProgramResource* res) {
+        fProgramResources.push_back(res);
+    }
+
+private:
+    void convertRefToPendingExecution() const;
+
+    void completedExecution() const {
+        this->validate();
+        --fPendingExecutions;
+        if (0 == fRefCnt && 0 == fPendingExecutions) {
+            SkDELETE(this);
+        }
+    }
+
+    mutable int32_t fRefCnt;
+    // Count of deferred executions not yet issued to the 3D API.
+    mutable int32_t fPendingExecutions;
+
+    SkSTArray<4, const GrProgramResource*, true> fProgramResources;
+
+    // Only this class can access convertRefToPendingExecution() and completedExecution().
+    template <typename T> friend class GrProgramElementRef;
+
+    typedef SkNoncopyable INHERITED;
+};
+
+#endif