Adds blocking file locks.

runtime/bin/file_linux.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_LINUX)
 
 #include "bin/file.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 118 matching lines @@
 
 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:
+    case File::kLockBlockingShared:
       fl.l_type = F_RDLCK;
       break;
     case File::kLockExclusive:
+    case File::kLockBlockingExclusive:
       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;
+  int cmd = F_SETLK;
+  if ((lock == File::kLockBlockingShared) ||
+      (lock == File::kLockBlockingExclusive)) {
+    cmd = F_SETLKW;
+  }
+  return TEMP_FAILURE_RETRY(fcntl(handle_->fd(), cmd, &fl)) != -1;
 }
 
 
 int64_t File::Length() {
   ASSERT(handle_->fd() >= 0);
   struct stat64 st;
   if (TEMP_FAILURE_RETRY(fstat64(handle_->fd(), &st)) == 0) {
     return st.st_size;
   }
   return -1;
@@ skipping 350 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_LINUX)