Add support for file locking

runtime/bin/file_android.cc

Index: runtime/bin/file_android.cc
diff --git a/runtime/bin/file_android.cc b/runtime/bin/file_android.cc
index 410fa0fbb84bb58c9996c5b5a1c81f67e6775103..3c2fb6baa8fb3a72852b711a52c02315cc0a33df 100644
--- a/runtime/bin/file_android.cc
+++ b/runtime/bin/file_android.cc
@@ -111,6 +111,30 @@ bool File::Flush() {
 }
 
 
+bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
+  ASSERT(handle_->fd() >= 0);

[kustermann, 2015/01/08 12:54:27]

ASSERT(end > start);

[Søren Gjesse, 2015/01/09 13:06:20]

Done.

+  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;
+  int rc = fcntl(handle_->fd(), F_SETLK, &fl);

[kustermann, 2015/01/08 12:54:27]

Add a comment that F_SETLK does not block but rather returns with
EACCESS/EAGAIN.

[Søren Gjesse, 2015/01/09 13:06:20]

Done.

+  return rc != -1;
+}
+
+
 int64_t File::Length() {
   ASSERT(handle_->fd() >= 0);
   struct stat st;