Convert child FPs from refs to pending executions when parent converts

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 GrGpuResourceRef;
 
 /**
- * Base class for GrProcessor. GrDrawState uses this to manage
- * transitioning a GrProcessor 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.
+ * Base class for GrProcessor. This exists to manage transitioning a GrProcessor from being owned by
+ * a client to being scheduled for execution. While a GrProcessor is ref'ed by drawing code its
+ * GrGpu resources must also be ref'ed to prevent incorrectly recycling them through the cache.
+ * However, once the GrProcessor is baked into a GrPipeline and the drawing code has stopped ref'ing
+ * it, it's internal resources can be recycled in some cases.
  *
- * All GrGpuResource objects owned by a GrProgramElement or derived classes (either directly or
- * indirectly) must be wrapped in a GrGpuResourceRef and registered with the GrProgramElement using
- * addGpuResource(). This allows the regular refs to be converted to pending IO events
- * when the program element is scheduled for deferred execution.
+ * We track this using two types of refs on GrProgramElement. A regular ref is owned by any client
+ * that may continue to issue draws that use the GrProgramElement. The GrPipeline owns "pending
+ * executions" instead of refs. A pending execution is cleared by ~GrPipeline().
+ *
+ * While a GrProgramElement is ref'ed any resources it owns are also ref'ed. However, once it gets
+ * into the state where it has pending executions AND no refs then it converts its ownership of
+ * its GrGpuResources from refs to pending IOs. The pending IOs allow the cache to track when it is
+ * safe to recycle a resource even though we still have buffered GrBatches that read or write to the
+ * the resource.
+ *
+ * To make this work all GrGpuResource objects owned by a GrProgramElement or derived classes
+ * (either directly or indirectly) must be wrapped in a GrGpuResourceRef and registered with the
+ * GrProgramElement using addGpuResource(). This allows the regular refs to be converted to pending
+ * IO events when the program element is scheduled for deferred execution.
+ *
+ * Moreover, a GrProgramElement that in turn owns other GrProgramElements must convert its ownership
+ * of its children to pending executions when its ref count reaches zero so that the GrGpuResources
+ * owned by the children GrProgramElements are correctly converted from ownership by ref to
+ * ownership by pending IO. Any GrProgramElement hierarchy is managed by subclasses which must
+ * implement notifyRefCntIsZero() in order to convert refs of children to pending executions.
  */
 class GrProgramElement : public SkNoncopyable {
 public:
     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 {
         this->validate();
         // Once the ref cnt reaches zero it should never be ref'ed again.
         SkASSERT(fRefCnt > 0);
         ++fRefCnt;
         this->validate();
     }
 
     void unref() const {
         this->validate();
         --fRefCnt;
         if (0 == fRefCnt) {
+            this->notifyRefCntIsZero();
             if (0 == fPendingExecutions) {
                 delete this;
                 return;
             } else {
                 this->removeRefs();
             }
         }
         this->validate();
     }
 
@@ skipping 14 matching lines @@
     GrProgramElement() : fRefCnt(1), fPendingExecutions(0), fUniqueID(CreateUniqueID()) {}
 
     /** 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
         GrGpuResourceRef is registered its setResource must not be called.
      */
     void addGpuResource(const GrGpuResourceRef* res) {
         fGpuResources.push_back(res);
     }
 
-private:
-    static uint32_t CreateUniqueID();
-
     void addPendingExecution() const {
         this->validate();
         SkASSERT(fRefCnt > 0);
         if (0 == fPendingExecutions) {
             this->addPendingIOs();
         }
         ++fPendingExecutions;
         this->validate();
     }
 
     void completedExecution() const {
         this->validate();
         --fPendingExecutions;
         if (0 == fPendingExecutions) {
             if (0 == fRefCnt) {
                 delete this;
                 return;
             } else {
                 this->pendingIOComplete();
             }
         }
         this->validate();
     }
 
+private:
+    /** This will be called when the ref cnt is zero. The object may or may not have pending
+        executions. */
+    virtual void notifyRefCntIsZero() const = 0;
+
+    static uint32_t CreateUniqueID();
+
     void removeRefs() const;
     void addPendingIOs() const;
     void pendingIOComplete() const;
 
     mutable int32_t fRefCnt;
     // Count of deferred executions not yet issued to the 3D API.
     mutable int32_t fPendingExecutions;
     uint32_t        fUniqueID;
 
     SkSTArray<4, const GrGpuResourceRef*, true> fGpuResources;
 
     // Only this class can access addPendingExecution() and completedExecution().
     template <typename T> friend class GrPendingProgramElement;
 
     typedef SkNoncopyable INHERITED;
 };
 
 #endif