xl: Simplify blockingWriter and its usage. (#1373)

This removes odd races since we don't need to
track errors and avoids locking. All we need
is a Wait() and Done() waitgroup.

xl-v1-blockingwriter.go

@@ -25,43 +25,26 @@ import (
 type blockingWriteCloser struct {
 	writer  io.WriteCloser  // Embedded writer.
 	release *sync.WaitGroup // Waitgroup for atomicity.
-	mutex   *sync.Mutex     // Mutex for thread safety.
 	err     error
 }
 
 // Write to the underlying writer.
 func (b *blockingWriteCloser) Write(data []byte) (int, error) {
-	n, err := b.writer.Write(data)
-	if err != nil {
-		b.mutex.Lock()
-		b.err = err
-		b.mutex.Unlock()
-	}
-	return n, b.err
+	return b.writer.Write(data)
 }
 
 // Close blocks until another goroutine calls Release(error). Returns
 // error code if either writer fails or Release is called with an error.
 func (b *blockingWriteCloser) Close() error {
 	err := b.writer.Close()
-	if err != nil {
-		b.mutex.Lock()
-		b.err = err
-		b.mutex.Unlock()
-	}
 	b.release.Wait()
-	return b.err
+	return err
 }
 
 // Release the Close, causing it to unblock. Only call this
 // once. Calling it multiple times results in a panic.
-func (b *blockingWriteCloser) Release(err error) {
+func (b *blockingWriteCloser) Release() {
 	b.release.Done()
-	if err != nil {
-		b.mutex.Lock()
-		b.err = err
-		b.mutex.Unlock()
-	}
 	return
 }
 
@@ -74,7 +57,6 @@ func newBlockingWriteCloser(writer io.WriteCloser) *blockingWriteCloser {
 	wg.Add(1)
 	return &blockingWriteCloser{
 		writer:  writer,
-		mutex:   &sync.Mutex{},
 		release: wg,
 	}
 }

xl-v1-createfile.go

@@ -129,6 +129,9 @@ func (xl XL) getFileQuorumVersionMap(volume, path string) map[int]int64 {
 // WriteErasure reads predefined blocks, encodes them and writes to
 // configured storage disks.
 func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *blockingWriteCloser) {
+	// Release the block writer upon function return.
+	defer bwriter.Release()
+
 	// Get available quorum for existing file path.
 	_, higherVersion := xl.getQuorumDisks(volume, path)
 	// Increment to have next higher version.
@@ -163,7 +166,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 			// Remove previous temp writers for any failure.
 			xl.cleanupCreateFileOps(volume, path, append(writers, metadataWriters...)...)
 			reader.CloseWithError(errWriteQuorum)
-			bwriter.Release(errWriteQuorum)
 			return
 		}
 
@@ -186,7 +188,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 			// Remove previous temp writers for any failure.
 			xl.cleanupCreateFileOps(volume, path, append(writers, metadataWriters...)...)
 			reader.CloseWithError(errWriteQuorum)
-			bwriter.Release(errWriteQuorum)
 			return
 		}
 
@@ -207,7 +208,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 				// Remove all temp writers.
 				xl.cleanupCreateFileOps(volume, path, append(writers, metadataWriters...)...)
 				reader.CloseWithError(err)
-				bwriter.Release(err)
 				return
 			}
 		}
@@ -223,7 +223,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 				// Remove all temp writers.
 				xl.cleanupCreateFileOps(volume, path, append(writers, metadataWriters...)...)
 				reader.CloseWithError(err)
-				bwriter.Release(err)
 				return
 			}
 
@@ -233,7 +232,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 				// Remove all temp writers upon error.
 				xl.cleanupCreateFileOps(volume, path, append(writers, metadataWriters...)...)
 				reader.CloseWithError(err)
-				bwriter.Release(err)
 				return
 			}
 
@@ -248,7 +246,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 					// Remove all temp writers upon error.
 					xl.cleanupCreateFileOps(volume, path, append(writers, metadataWriters...)...)
 					reader.CloseWithError(err)
-					bwriter.Release(err)
 					return
 				}
 				if sha512Writers[index] != nil {
@@ -298,7 +295,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 			// Remove temporary files.
 			xl.cleanupCreateFileOps(volume, path, append(writers, metadataWriters...)...)
 			reader.CloseWithError(err)
-			bwriter.Release(err)
 			return
 		}
 	}
@@ -322,9 +318,6 @@ func (xl XL) writeErasure(volume, path string, reader *io.PipeReader, bwriter *b
 		metadataWriters[index].Close()
 	}
 
-	// Release the blocking writer.
-	bwriter.Release(nil)
-
 	// Close the pipe reader and return.
 	reader.Close()
 	return