Add support for file locking

runtime/bin/file_macos.cc

 // Copyright (c) 2012, 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.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/file.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 93 matching lines @@
   return TEMP_FAILURE_RETRY(ftruncate(handle_->fd(), length)) != -1;
 }
 
 
 bool File::Flush() {
   ASSERT(handle_->fd() >= 0);
   return NO_RETRY_EXPECTED(fsync(handle_->fd())) != -1;
 }
 
 
+bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
+  ASSERT(handle_->fd() >= 0);
+  ASSERT(end == -1 || end > start);
+  struct flock fl;
+  switch (lock) {
+    case File::kLockUnlock:
+      fl.l_type = F_UNLCK;
+      break;
+    case File::kLockShared:
+      fl.l_type = F_RDLCK;
+      break;
+    case File::kLockExclusive:
+      fl.l_type = F_WRLCK;
+      break;
+    default:
+      return false;
+  }
+  fl.l_whence = SEEK_SET;
+  fl.l_start = start;
+  fl.l_len = end == -1 ? 0 : end - start;
+  // fcntl does not block, but fails if the lock cannot be acquired.
+  int rc = fcntl(handle_->fd(), F_SETLK, &fl);
+  return rc != -1;
+}
+
+
 int64_t File::Length() {
   ASSERT(handle_->fd() >= 0);
   struct stat st;
   if (NO_RETRY_EXPECTED(fstat(handle_->fd(), &st)) == 0) {
     return st.st_size;
   }
   return -1;
 }
 
 
@@ skipping 268 matching lines @@
   return (file_1_info.st_ino == file_2_info.st_ino &&
           file_1_info.st_dev == file_2_info.st_dev) ?
       File::kIdentical :
       File::kDifferent;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)