[Lldb-commits] [PATCH] D157347: [lldb] Fix data race in NativeFile

[Augusto Noronha via Phabricator via lldb-commits]

augusto2112 added inline comments.


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Comment at: lldb/source/Host/common/File.cpp:609
       num_bytes = bytes_written;
-  } else if (StreamIsValid()) {
+  } else if (ValueGuard stream_guard = StreamIsValid()) {
     bytes_written = ::fwrite(buf, 1, num_bytes, m_stream);
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bulbazord wrote:
> augusto2112 wrote:
> > One thing that's not super obvious for people reading this is that `descriptor_guard` is still in scope in the else branch (due to C++'s weird scoping rules when it comes to declaring variables inside `if` statements), and will keep the descriptor mutex locked which is probably not what you intended. I don't think this affects the correctness of this implementation at the moment, but could be dangerous with further changes on top of this one.
> If that's true, then this change needs further adjustment. `GetStream` acquires the `ValueGuard`s in the opposite order, meaning Thread 1 can call this function and acquire `descriptor_guard` while Thread 2 can call `GetStream` and acquire `stream_guard` at the same time. Then they're both waiting on the other lock (deadlock).
You're right, nice catch.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157347/new/

https://reviews.llvm.org/D157347