[PATCH] D124607: Add an error message to the default SIGPIPE handler

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai added a comment.

In D124607#3536329 <https://reviews.llvm.org/D124607#3536329>, @jhenderson wrote:

> Both llvm-symbolizer and llvm-cxxfilt, if called without positional arguments, are run interactively, essentially taking a line of input then writing some output before waiting for more input. This would allow you to force output to be written (by writing to stdin) after the pipe has been closed. Maybe that'll solve the issue, although I'm not sure I understand why the python script doesn't work in its current form: llvm-nm should try to write many bytes of output (> 1 byte), but the pipe is closed after the very first byte is written. Before going and changing the script, I'd like to understand whether this statement is actually true, and if so, why:
>
>> That does not appear to be enough. You can either run a tool that runs longer or run llvm-nm with something that produces more output.

If you have an idea for how I can verify this, I'd love to help. Without any tracing/debugging as proof, the way I guess I reason about it is that the process writes to the pipe asynchronously without regard to how much is read from the pipe. So if the write finishes before the pipe is closed, it finishes. Namely, reading a single byte from the pipe rather than all of them does not prevent all the bytes from being written to it before it is closed.
As I said, I am not sure why the test only works when there is more output. All I know for sure is that I've tried it on multiple machines with a shared library build with the same results.


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https://reviews.llvm.org/D124607