Adds blocking file locks.

runtime/bin/file_linux.cc

Index: runtime/bin/file_linux.cc
diff --git a/runtime/bin/file_linux.cc b/runtime/bin/file_linux.cc
index 2e47d74978a486a0fd1a202b9f365526459ac946..eab92d5361ea847ad8e7b8064a6d47c9f86bdecf 100644
--- a/runtime/bin/file_linux.cc
+++ b/runtime/bin/file_linux.cc
@@ -136,9 +136,11 @@ bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
       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:
@@ -147,9 +149,12 @@ bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
   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;
 }