Mutexes in pixelrefs were done very sloppily initially. The code (a) assumes all

pixelref subclasses want a mutex to guard their lock/unlock virtuals, and (b)
most subclasses use the same mutex for *all* of their instances, even when there
is no explicit need to guard modifying one instances with another.

When we try drawing bitmaps from multiple threads, we are seeing a lot of slow-
down from these mutexes. This CL has two changes to try to speed things up.

1. Add setPreLocked(), for pixelrefs who never need the onLockPixels
virtual to be called. This speeds up those subclasses in multithreaded environs
as it avoids the mutex lock all together (e.g. SkMallocPixelRef).

2. Add setMutex() to allow a subclass to change the mutex choice. ashmem wants
this, since its unflattening constructor cannot pass down the null, it needs
to cleanup afterwards.
Review URL: https://codereview.appspot.com/6199075

git-svn-id: http://skia.googlecode.com/svn/trunk@3985 2bbb7eff-a529-9590-31e7-b0007b416f81

diff --git a/include/core/SkPixelRef.h b/include/core/SkPixelRef.h
index c902765..5c24d67 100644 (file)
--- a/include/core/SkPixelRef.h
+++ b/include/core/SkPixelRef.h
@@ -43,9 +43,10 @@ public:
     */
     SkColorTable* colorTable() const { return fColorTable; }
 
-    /** Return the current lockcount (defaults to 0)
-    */
-    int getLockCount() const { return fLockCount; }
+    /**
+     *  Returns true if the lockcount > 0
+     */
+    bool isLocked() const { return fLockCount > 0; }
 
     /** Call to access the pixel memory, which is returned. Balance with a call
         to unlockPixels().
@@ -169,6 +170,18 @@ protected:
     SkPixelRef(SkFlattenableReadBuffer&, SkBaseMutex*);
     virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
 
+    // only call from constructor. Flags this to always be locked, removing
+    // the need to grab the mutex and call onLockPixels/onUnlockPixels.
+    // Performance tweak to avoid those calls (esp. in multi-thread use case).
+    void setPreLocked(void* pixels, SkColorTable* ctable);
+
+    /**
+     *  If a subclass passed a particular mutex to the base constructor, it can
+     *  override that to go back to the default mutex by calling this. However,
+     *  this should only be called from within the subclass' constructor.
+     */
+    void useDefaultMutex() { this->setMutex(NULL); }
+
 private:
 
     SkBaseMutex*    fMutex; // must remain in scope for the life of this object
@@ -182,6 +195,10 @@ private:
 
     // can go from false to true, but never from true to false
     bool    fIsImmutable;
+    // only ever set in constructor, const after that
+    bool    fPreLocked;
+
+    void setMutex(SkBaseMutex* mutex);
 
     typedef SkFlattenable INHERITED;
 };

diff --git a/include/core/SkThread_platform.h b/include/core/SkThread_platform.h
index 3514775..7041aa4 100644 (file)
--- a/include/core/SkThread_platform.h
+++ b/include/core/SkThread_platform.h
@@ -140,6 +140,8 @@ struct SkBaseMutex {
 // Special case used when the static mutex must be available globally.
 #define SK_DECLARE_GLOBAL_MUTEX(name)   SkBaseMutex  name = { PTHREAD_MUTEX_INITIALIZER }
 
+#define SK_DECLARE_MUTEX_ARRAY(name, count)    SkBaseMutex name[count] = { PTHREAD_MUTEX_INITIALIZER }
+
 // A normal mutex that requires to be initialized through normal C++ construction,
 // i.e. when it's a member of another class, or allocated on the heap.
 class SkMutex : public SkBaseMutex, SkNoncopyable {
@@ -171,8 +173,9 @@ private:
 
 typedef SkMutex SkBaseMutex;
 
-#define SK_DECLARE_STATIC_MUTEX(name)  static SkBaseMutex  name
-#define SK_DECLARE_GLOBAL_MUTEX(name)  SkBaseMutex  name
+#define SK_DECLARE_STATIC_MUTEX(name)           static SkBaseMutex  name
+#define SK_DECLARE_GLOBAL_MUTEX(name)           SkBaseMutex  name
+#define SK_DECLARE_MUTEX_ARRAY(name, count)     SkBaseMutex name[count]
 
 #endif // !SK_USE_POSIX_THREADS
 

diff --git a/src/core/SkBitmap.cpp b/src/core/SkBitmap.cpp
index da87e77..6b99145 100644 (file)
--- a/src/core/SkBitmap.cpp
+++ b/src/core/SkBitmap.cpp
@@ -297,7 +297,7 @@ err:
 void SkBitmap::updatePixelsFromRef() const {
     if (NULL != fPixelRef) {
         if (fPixelLockCount > 0) {
-            SkASSERT(fPixelRef->getLockCount() > 0);
+            SkASSERT(fPixelRef->isLocked());
 
             void* p = fPixelRef->pixels();
             if (NULL != p) {
@@ -1525,7 +1525,7 @@ void SkBitmap::validate() const {
 #if 0   // these asserts are not thread-correct, so disable for now
     if (fPixelRef) {
         if (fPixelLockCount > 0) {
-            SkASSERT(fPixelRef->getLockCount() > 0);
+            SkASSERT(fPixelRef->isLocked());
         } else {
             SkASSERT(NULL == fPixels);
             SkASSERT(NULL == fColorTable);

diff --git a/src/core/SkBitmapProcShader.cpp b/src/core/SkBitmapProcShader.cpp
index 3abfc8d..f76bc09 100644 (file)
--- a/src/core/SkBitmapProcShader.cpp
+++ b/src/core/SkBitmapProcShader.cpp
@@ -173,7 +173,7 @@ void SkBitmapProcShader::shadeSpan(int x, int y, SkPMColor dstC[], int count) {
 
     SkASSERT(state.fBitmap->getPixels());
     SkASSERT(state.fBitmap->pixelRef() == NULL ||
-             state.fBitmap->pixelRef()->getLockCount());
+             state.fBitmap->pixelRef()->isLocked());
 
     for (;;) {
         int n = count;
@@ -217,7 +217,7 @@ void SkBitmapProcShader::shadeSpan16(int x, int y, uint16_t dstC[], int count) {
 
     SkASSERT(state.fBitmap->getPixels());
     SkASSERT(state.fBitmap->pixelRef() == NULL ||
-             state.fBitmap->pixelRef()->getLockCount());
+             state.fBitmap->pixelRef()->isLocked());
 
     for (;;) {
         int n = count;

diff --git a/src/core/SkMallocPixelRef.cpp b/src/core/SkMallocPixelRef.cpp
index 313a26e..14a0646 100644 (file)
--- a/src/core/SkMallocPixelRef.cpp
+++ b/src/core/SkMallocPixelRef.cpp
@@ -18,6 +18,8 @@ SkMallocPixelRef::SkMallocPixelRef(void* storage, size_t size,
     fSize = size;
     fCTable = ctable;
     SkSafeRef(ctable);
+    
+    this->setPreLocked(fStorage, fCTable);
 }
 
 SkMallocPixelRef::~SkMallocPixelRef() {
@@ -57,6 +59,8 @@ SkMallocPixelRef::SkMallocPixelRef(SkFlattenableReadBuffer& buffer)
     } else {
         fCTable = NULL;
     }
+
+    this->setPreLocked(fStorage, fCTable);
 }
 
 SK_DEFINE_FLATTENABLE_REGISTRAR(SkMallocPixelRef)

diff --git a/src/core/SkPixelRef.cpp b/src/core/SkPixelRef.cpp
index f01fbea..88ce76f 100644 (file)
--- a/src/core/SkPixelRef.cpp
+++ b/src/core/SkPixelRef.cpp
@@ -9,7 +9,28 @@
 #include "SkFlattenable.h"
 #include "SkThread.h"
 
-SK_DECLARE_STATIC_MUTEX(gPixelRefMutex);
+// must be a power-of-2. undef to just use 1 mutex
+#define PIXELREF_MUTEX_RING_COUNT       32
+
+#ifdef PIXELREF_MUTEX_RING_COUNT
+    static int32_t gPixelRefMutexRingIndex;
+    static SK_DECLARE_MUTEX_ARRAY(gPixelRefMutexRing, PIXELREF_MUTEX_RING_COUNT);
+#else
+    SK_DECLARE_STATIC_MUTEX(gPixelRefMutex);
+#endif
+
+SkBaseMutex* get_default_mutex() {
+#ifdef PIXELREF_MUTEX_RING_COUNT
+    // atomic_inc might be overkill here. It may be fine if once in a while
+    // we hit a race-condition and two subsequent calls get the same index...
+    int index = sk_atomic_inc(&gPixelRefMutexRingIndex);
+    return &gPixelRefMutexRing[index & (PIXELREF_MUTEX_RING_COUNT - 1)];
+#else
+    return &gPixelRefMutex;
+#endif
+}
+
+///////////////////////////////////////////////////////////////////////////////
 
 extern int32_t SkNextPixelRefGenerationID();
 int32_t SkNextPixelRefGenerationID() {
@@ -23,30 +44,46 @@ int32_t SkNextPixelRefGenerationID() {
     return genID;
 }
 
+///////////////////////////////////////////////////////////////////////////////
 
-SkPixelRef::SkPixelRef(SkBaseMutex* mutex) {
+void SkPixelRef::setMutex(SkBaseMutex* mutex) {
     if (NULL == mutex) {
-        mutex = &gPixelRefMutex;
+        mutex = get_default_mutex();
     }
     fMutex = mutex;
+}
+
+// just need a > 0 value, so pick a funny one to aid in debugging
+#define SKPIXELREF_PRELOCKED_LOCKCOUNT     123456789
+
+SkPixelRef::SkPixelRef(SkBaseMutex* mutex) : fPreLocked(false) {
+    this->setMutex(mutex);
     fPixels = NULL;
     fColorTable = NULL; // we do not track ownership of this
     fLockCount = 0;
     fGenerationID = 0;  // signal to rebuild
     fIsImmutable = false;
+    fPreLocked = false;
 }
 
 SkPixelRef::SkPixelRef(SkFlattenableReadBuffer& buffer, SkBaseMutex* mutex)
         : INHERITED(buffer) {
-    if (NULL == mutex) {
-        mutex = &gPixelRefMutex;
-    }
-    fMutex = mutex;
+    this->setMutex(mutex);
     fPixels = NULL;
     fColorTable = NULL; // we do not track ownership of this
     fLockCount = 0;
     fGenerationID = 0;  // signal to rebuild
     fIsImmutable = buffer.readBool();
+    fPreLocked = false;
+}
+
+void SkPixelRef::setPreLocked(void* pixels, SkColorTable* ctable) {
+    // only call me in your constructor, otherwise fLockCount tracking can get
+    // out of sync.
+    fPixels = pixels;
+    fColorTable = ctable;
+    fLockCount = SKPIXELREF_PRELOCKED_LOCKCOUNT;
+    fPreLocked = true;
 }
 
 void SkPixelRef::flatten(SkFlattenableWriteBuffer& buffer) const {
@@ -55,21 +92,29 @@ void SkPixelRef::flatten(SkFlattenableWriteBuffer& buffer) const {
 }
 
 void SkPixelRef::lockPixels() {
-    SkAutoMutexAcquire  ac(*fMutex);
+    SkASSERT(!fPreLocked || SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount);
 
-    if (1 == ++fLockCount) {
-        fPixels = this->onLockPixels(&fColorTable);
+    if (!fPreLocked) {
+        SkAutoMutexAcquire  ac(*fMutex);
+
+        if (1 == ++fLockCount) {
+            fPixels = this->onLockPixels(&fColorTable);
+        }
     }
 }
 
 void SkPixelRef::unlockPixels() {
-    SkAutoMutexAcquire  ac(*fMutex);
-
-    SkASSERT(fLockCount > 0);
-    if (0 == --fLockCount) {
-        this->onUnlockPixels();
-        fPixels = NULL;
-        fColorTable = NULL;
+    SkASSERT(!fPreLocked || SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount);
+    
+    if (!fPreLocked) {
+        SkAutoMutexAcquire  ac(*fMutex);
+
+        SkASSERT(fLockCount > 0);
+        if (0 == --fLockCount) {
+            this->onUnlockPixels();
+            fPixels = NULL;
+            fColorTable = NULL;
+        }
     }
 }
 

diff --git a/src/images/SkImageRefPool.cpp b/src/images/SkImageRefPool.cpp
index bfa933e..c24dba0 100644 (file)
--- a/src/images/SkImageRefPool.cpp
+++ b/src/images/SkImageRefPool.cpp
@@ -59,7 +59,7 @@ void SkImageRefPool::setRAMUsed(size_t limit) {
     
     while (NULL != ref && fRAMUsed > limit) {
         // only purge it if its pixels are unlocked
-        if (0 == ref->getLockCount() && ref->fBitmap.getPixels()) {
+        if (!ref->isLocked() && ref->fBitmap.getPixels()) {
             size_t size = ref->ramUsed();
             SkASSERT(size <= fRAMUsed);
             fRAMUsed -= size;
@@ -181,10 +181,10 @@ void SkImageRefPool::dump() const {
     SkImageRef* ref = fHead;
     
     while (ref != NULL) {
-        SkDebugf("  [%3d %3d %d] ram=%d data=%d locks=%d %s\n", ref->fBitmap.width(),
+        SkDebugf("  [%3d %3d %d] ram=%d data=%d locked=%d %s\n", ref->fBitmap.width(),
                  ref->fBitmap.height(), ref->fBitmap.config(),
                  ref->ramUsed(), (int)ref->fStream->getLength(),
-                 ref->getLockCount(), ref->getURI());
+                 ref->isLocked(), ref->getURI());
         
         ref = ref->fNext;
     }

diff --git a/src/ports/SkImageRef_ashmem.cpp b/src/ports/SkImageRef_ashmem.cpp
index f1fb829..6ea5c95 100644 (file)
--- a/src/ports/SkImageRef_ashmem.cpp
+++ b/src/ports/SkImageRef_ashmem.cpp
@@ -41,6 +41,8 @@ SkImageRef_ashmem::SkImageRef_ashmem(SkStream* stream,
     fRec.fPinned = false;
             
     fCT = NULL;
+            
+    this->useDefaultMutex();   // we don't need/want the shared imageref mutex
 }
 
 SkImageRef_ashmem::~SkImageRef_ashmem() {
@@ -235,6 +237,7 @@ SkImageRef_ashmem::SkImageRef_ashmem(SkFlattenableReadBuffer& buffer)
         buffer.read(buf, length);
         setURI(buf, length);
     }
+    this->useDefaultMutex();   // we don't need/want the shared imageref mutex
 }
 
 SkPixelRef* SkImageRef_ashmem::Create(SkFlattenableReadBuffer& buffer) {