[lldb-dev] [PATCH] Unexpected group-stop with threading under Linux

[Andrew MacPherson]

This patch addresses a bug where in a multi-threaded program a new signal
from the inferior may be received before all group-stop messages from an
earlier signal have been handled. The attached .cpp file exposes the issue:

   - clang++ -o thread thread.cpp -lpthread -g -O0
   - lldb ./thread
   - r
   - hit Ctrl-C
   - br set -f thread.cpp -l 11
   - c
   - <hang>

A breakpoint is usually hit before all the group-stop messages involved in
restarting the process are handled and the internal state then gets out of
sync.

The attached patch solves the issue and all unit tests pass, I'm not a
ptrace expert though so there may be a more appropriate fix. The group-stop
handling was taken from the existing ProcessMonitor::MonitorCallback.

Thanks,

Andrew
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