Bug 1439047 - Part 1: Make StartupCache::PutBuffer take ownership of the buffer. r=froydnj

This avoids a redundant alloc and copy in `PutBuffer`. All existing callers
were destroying the passed in buffer after the call.

--HG--
extra : rebase_source : 39a21686becedf32c38e58fa832ae47845b2f5e0

dom/xbl/nsXBLDocumentInfo.cpp

@@ -298,7 +298,7 @@ nsXBLDocumentInfo::WritePrototypeBindings()
   rv = NewBufferFromStorageStream(storageStream, &buf, &len);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  return startupCache->PutBuffer(spec.get(), buf.get(), len);
+  return startupCache->PutBuffer(spec.get(), Move(buf), len);
 }
 
 void

dom/xul/nsXULPrototypeCache.cpp

@@ -446,7 +446,7 @@ nsXULPrototypeCache::FinishOutputStream(nsIURI* uri)
         rv = PathifyURI(uri, spec);
         if (NS_FAILED(rv))
             return NS_ERROR_NOT_AVAILABLE;
-        rv = sc->PutBuffer(spec.get(), buf.get(), len);
+        rv = sc->PutBuffer(spec.get(), Move(buf), len);
         if (NS_SUCCEEDED(rv)) {
             mOutputStreamTable.Remove(uri);
             mStartupCacheURITable.PutEntry(uri);
@@ -591,7 +591,7 @@ nsXULPrototypeCache::BeginCaching(nsIURI* aURI)
             buf = MakeUnique<char[]>(len);
             rv = inputStream->Read(buf.get(), len, &amtRead);
             if (NS_SUCCEEDED(rv) && len == amtRead)
-              rv = startupCache->PutBuffer(kXULCacheInfoKey, buf.get(), len);
+              rv = startupCache->PutBuffer(kXULCacheInfoKey, Move(buf), len);
             else {
                 rv = NS_ERROR_UNEXPECTED;
             }

js/xpconnect/loader/mozJSLoaderUtils.cpp

@@ -62,8 +62,11 @@ WriteCachedScript(StartupCache* cache, nsACString& uri, JSContext* cx,
     size_t size = buffer.length();
     if (size > UINT32_MAX)
         return NS_ERROR_FAILURE;
+
+    // Move the vector buffer into a unique pointer buffer.
+    UniquePtr<char[]> buf(reinterpret_cast<char*>(buffer.extractOrCopyRawBuffer()));
     nsresult rv = cache->PutBuffer(PromiseFlatCString(uri).get(),
-                                   reinterpret_cast<char*>(buffer.begin()),
+                                   Move(buf),
                                    size);
     return rv;
 }

startupcache/StartupCache.cpp

@@ -302,7 +302,7 @@ StartupCache::GetBuffer(const char* id, UniquePtr<char[]>* outbuf, uint32_t* len
 
 // Makes a copy of the buffer, client retains ownership of inbuf.
 nsresult
-StartupCache::PutBuffer(const char* id, const char* inbuf, uint32_t len)
+StartupCache::PutBuffer(const char* id, UniquePtr<char[]>&& inbuf, uint32_t len)
 {
   NS_ASSERTION(NS_IsMainThread(), "Startup cache only available on main thread");
   WaitOnWriteThread();
@@ -310,9 +310,6 @@ StartupCache::PutBuffer(const char* id, const char* inbuf, uint32_t len)
     return NS_ERROR_NOT_AVAILABLE;
   }
 
-  auto data = MakeUnique<char[]>(len);
-  memcpy(data.get(), inbuf, len);
-
   nsCString idStr(id);
   // Cache it for now, we'll write all together later.
   CacheEntry* entry;
@@ -330,7 +327,7 @@ StartupCache::PutBuffer(const char* id, const char* inbuf, uint32_t len)
   }
 #endif
 
-  entry = new CacheEntry(Move(data), len);
+  entry = new CacheEntry(Move(inbuf), len);
   mTable.Put(idStr, entry);
   mPendingWrites.AppendElement(idStr);
   return ResetStartupWriteTimer();

startupcache/StartupCache.h

@@ -113,8 +113,8 @@ public:
   // Returns a buffer that was previously stored, caller takes ownership.
   nsresult GetBuffer(const char* id, UniquePtr<char[]>* outbuf, uint32_t* length);
 
-  // Stores a buffer. Caller keeps ownership, we make a copy.
+  // Stores a buffer. Caller yields ownership.
-  nsresult PutBuffer(const char* id, const char* inbuf, uint32_t length);
+  nsresult PutBuffer(const char* id, UniquePtr<char[]>&& inbuf, uint32_t length);
 
   // Removes the cache file.
   void InvalidateCache();

startupcache/test/TestStartupCache.cpp

@@ -96,7 +96,7 @@ TEST_F(TestStartupCache, StartupWriteRead)
   UniquePtr<char[]> outbuf;
   uint32_t len;
 
-  rv = sc->PutBuffer(id, buf, strlen(buf) + 1);
+  rv = sc->PutBuffer(id, UniquePtr<char[]>(strdup(buf)), strlen(buf) + 1);
   EXPECT_TRUE(NS_SUCCEEDED(rv));
 
   rv = sc->GetBuffer(id, &outbuf, &len);
@@ -122,7 +122,7 @@ TEST_F(TestStartupCache, WriteInvalidateRead)
   StartupCache* sc = StartupCache::GetSingleton();
   ASSERT_TRUE(sc);
 
-  rv = sc->PutBuffer(id, buf, strlen(buf) + 1);
+  rv = sc->PutBuffer(id, UniquePtr<char[]>(strdup(buf)), strlen(buf) + 1);
   EXPECT_TRUE(NS_SUCCEEDED(rv));
 
   sc->InvalidateCache();
@@ -177,7 +177,7 @@ TEST_F(TestStartupCache, WriteObject)
 
   // Since this is a post-startup write, it should be written and
   // available.
-  rv = sc->PutBuffer(id, buf.get(), len);
+  rv = sc->PutBuffer(id, Move(buf), len);
   EXPECT_TRUE(NS_SUCCEEDED(rv));
 
   UniquePtr<char[]> buf2;