optimize memory allocation during erasure-read by using temporary buffer pool. (#2259)

* XL/erasure-read: optimize memory allocation during erasure-read by using temporary buffer pool.

With the change the buffer needed during GetObject by erasureReadFile is allocated only once.

pkg/bpool/bpool_test.go

@@ -0,0 +1,53 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package bpool
+
+import "testing"
+
+func TestBytePool(t *testing.T) {
+	size := int64(10)
+	n := 16
+	pool := NewBytePool(size, n)
+	enBlocks := make([][]byte, n)
+
+	// Allocates all the 16 byte slices in the pool.
+	alloc := func() {
+		for i := range enBlocks {
+			var err error
+			enBlocks[i], err = pool.Get()
+			if err != nil {
+				t.Fatal("expected nil, got", err)
+			}
+			// Make sure the slice length is as expected.
+			if len(enBlocks[i]) != int(size) {
+				t.Fatalf("expected size %d, got %d", len(enBlocks[i]), size)
+			}
+		}
+	}
+
+	// Allocate everything in the pool.
+	alloc()
+	// Any Get() will fail when the pool does not have any free buffer.
+	_, err := pool.Get()
+	if err == nil {
+		t.Fatalf("expected %s, got nil", err)
+	}
+	// Reset - so that all the buffers are marked as unused.
+	pool.Reset()
+	// Allocation of all the buffers in the pool should succeed now.
+	alloc()
+}