Add IORef capability to GrSurfaceProxy objects - take 2

Re-landing of https://skia-review.googlesource.com/c/4734/ (Add IORef capability to GrSurfaceProxy objects) with fixes for:
 platforms that don't support discards.
 memory leak due to copying over of GrSurfaceProxy's creation ref to instantiated GrSurface in instantiate()

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4827
BUG=skia:

Change-Id: If0b695d5cafc5ef3fdd251c38262849d09e5d27f
Review-Url: https://codereview.chromium.org/2502923003

1 files changed, 85 insertions, 6 deletions

diff --git a/include/private/GrSurfaceProxy.h b/include/private/GrSurfaceProxy.h
index dd5ece1e2c..1ff6df809d 100644
--- a/include/private/GrSurfaceProxy.h
+++ b/include/private/GrSurfaceProxy.h
@@ -50,13 +50,29 @@ public:
 
     void validate() const {
 #ifdef SK_DEBUG    
-        SkASSERT(fRefCnt >= 0);
+        SkASSERT(fRefCnt >= 1);
+        SkASSERT(fPendingReads >= 0);
+        SkASSERT(fPendingWrites >= 0);
+        SkASSERT(fRefCnt + fPendingReads + fPendingWrites >= 1);
+
+        if (fTarget) {
+            SkASSERT(!fPendingReads && !fPendingWrites);
+            // The backing GrSurface can have more refs than the proxy if the proxy
+            // started off wrapping an external resource (that came in with refs).
+            // The GrSurface should never have fewer refs than the proxy however.
+            SkASSERT(fTarget->fRefCnt >= fRefCnt);
+        }
 #endif
     }
 
+    int32_t getProxyRefCnt_TestOnly() const;
+    int32_t getBackingRefCnt_TestOnly() const;
+    int32_t getPendingReadCnt_TestOnly() const;
+    int32_t getPendingWriteCnt_TestOnly() const;
+
 protected:
-    GrIORefProxy() : fRefCnt(1), fTarget(nullptr) {}
-    GrIORefProxy(sk_sp<GrSurface> surface) : fRefCnt(1) {
+    GrIORefProxy() : fTarget(nullptr), fRefCnt(1), fPendingReads(0), fPendingWrites(0) {}
+    GrIORefProxy(sk_sp<GrSurface> surface) : fRefCnt(1), fPendingReads(0), fPendingWrites(0) {
         // Since we're manually forwarding on refs & unrefs we don't want sk_sp doing
         // anything extra.
         fTarget = surface.release();
@@ -66,13 +82,76 @@ protected:
         // have forwarded on the unref call that got use here.
     }
 
-    // TODO: add the IO ref counts. Although if we can delay shader creation to flush time
-    // we may not even need to do that.
-    mutable int32_t fRefCnt;
+    // This GrIORefProxy was deferred before but has just been instantiated. To
+    // make all the reffing & unreffing work out we now need to transfer any deferred
+    // refs & unrefs to the new GrSurface
+    void transferRefs() {
+        SkASSERT(fTarget);
+
+        fTarget->fRefCnt += (fRefCnt-1); // don't xfer the proxy's creation ref
+        fTarget->fPendingReads += fPendingReads;
+        fTarget->fPendingWrites += fPendingWrites;
+
+        fPendingReads = 0;
+        fPendingWrites = 0;
+    }
 
     // For deferred proxies this will be null. For wrapped proxies it will point to the
     // wrapped resource.
     GrSurface* fTarget;
+
+private:
+    // This class is used to manage conversion of refs to pending reads/writes.
+    friend class GrGpuResourceRef;
+    template <typename, GrIOType> friend class GrPendingIOResource;
+
+    void addPendingRead() const {
+        this->validate();
+
+        if (fTarget) {
+            fTarget->addPendingRead();
+            return;
+        }
+
+        ++fPendingReads;
+    }
+
+    void completedRead() const {
+        this->validate();
+
+        if (fTarget) {
+            fTarget->completedRead();
+            return;
+        }
+    
+        SkFAIL("How was the read completed if the Proxy hasn't been instantiated?");
+    }
+
+    void addPendingWrite() const {
+        this->validate();
+
+        if (fTarget) {
+            fTarget->addPendingWrite();
+            return;
+        }
+
+        ++fPendingWrites;
+    }
+
+    void completedWrite() const {
+        this->validate();
+
+        if (fTarget) {
+            fTarget->completedWrite();
+            return;
+        }
+    
+        SkFAIL("How was the write completed if the Proxy hasn't been instantiated?");
+    }
+
+    mutable int32_t fRefCnt;
+    mutable int32_t fPendingReads;
+    mutable int32_t fPendingWrites;
 };
 
 class GrSurfaceProxy : public GrIORefProxy {