Adds blocking file locks.

sdk/lib/io/file_impl.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 
@@ skipping 901 matching lines @@
     _checkAvailable();
     var result = _ops.flush();
     if (result is OSError) {
       throw new FileSystemException("flush failed", path, result);
     }
   }
 
   static final int LOCK_UNLOCK = 0;
   static final int LOCK_SHARED = 1;
   static final int LOCK_EXCLUSIVE = 2;
+  static final int LOCK_BLOCKING_SHARED = 3;
+  static final int LOCK_BLOCKING_EXCLUSIVE = 4;
+
+  int _fileLockValue(FileLock fl) {
+    switch (fl) {
+      case FileLock.SHARED: return LOCK_SHARED;
+      case FileLock.EXCLUSIVE: return LOCK_EXCLUSIVE;
+      case FileLock.BLOCKING_SHARED: return LOCK_BLOCKING_SHARED;
+      case FileLock.BLOCKING_EXCLUSIVE: return LOCK_BLOCKING_EXCLUSIVE;
+      default: return -1;
+    }
+  }
 
   Future<RandomAccessFile> lock(
       [FileLock mode = FileLock.EXCLUSIVE, int start = 0, int end = -1]) {
     if ((mode is !FileLock) || (start is !int) || (end is !int)) {
       throw new ArgumentError();
     }
     if ((start < 0) || (end < -1) || ((end != -1) && (start >= end))) {
       throw new ArgumentError();
     }
-    int lock = (mode == FileLock.EXCLUSIVE) ? LOCK_EXCLUSIVE : LOCK_SHARED;
+    int lock = _fileLockValue(mode);
     return _dispatch(_FILE_LOCK, [null, lock, start, end])
         .then((response) {
           if (_isErrorResponse(response)) {
             throw _exceptionFromResponse(response, 'lock failed', path);
           }
           return this;
         });
   }
 
   Future<RandomAccessFile> unlock([int start = 0, int end = -1]) {
@@ skipping 14 matching lines @@
 
   void lockSync(
       [FileLock mode = FileLock.EXCLUSIVE, int start = 0, int end = -1]) {
     _checkAvailable();
     if ((mode is !FileLock) || (start is !int) || (end is !int)) {
       throw new ArgumentError();
     }
     if ((start < 0) || (end < -1) || ((end != -1) && (start >= end))) {
       throw new ArgumentError();
     }
-    int lock = (mode == FileLock.EXCLUSIVE) ? LOCK_EXCLUSIVE : LOCK_SHARED;
+    int lock = _fileLockValue(mode);
     var result = _ops.lock(lock, start, end);
     if (result is OSError) {
       throw new FileSystemException('lock failed', path, result);
     }
   }
 
   void unlockSync([int start = 0, int end = -1]) {
     _checkAvailable();
     if ((start is !int) || (end is !int)) {
       throw new ArgumentError();
@@ skipping 39 matching lines @@
   void _checkAvailable() {
     if (_asyncDispatched) {
       throw new FileSystemException("An async operation is currently pending",
                                     path);
     }
     if (closed) {
       throw new FileSystemException("File closed", path);
     }
   }
 }