Matthew Zipkin 73da2a8a52 http: prevent race condition between worker thread and I/O thread ...

This prevents a losing race condition that could prevent the server
from reading requests from an HTTP client.

A connected socket can either be written to or read from based on the
result of GenerateWaitSockets(). That method checks the HTTPRemoteClient
flag m_send_ready. If it's `true` the implication is that there is
data in the client's send buffer ready to go. Once that data is sent
and the buffer is empty, MaybeSendBytesFromBuffer() sets it `false` again.

The sad case was when a worker thread calling WriteReply() adds
data to the send buffer, but before it sets m_send_ready to `true`,
the I/O thread sends that data and empties the buffer. With the
buffer unexpectedly empty, WriteReply() sets m_send_ready to `true`.

The effect of this is that the socket will stay in "write" mode
with nothing to write. With nothing to write, MaybeSendBytesFromBuffer()
never sets it back to `false` and the socket is stuck forever.

2026-06-29 10:09:26 -04:00

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