win,pipe: minimal fix to uv_read_cb->uv_read_start recursion bug (#4784)

Starting a new read after uv_read_cb returns causes memory corruption on
the OVERLAPPED read_req if uv_read_stop+uv_read_start was called during
the callback after the latest refactoring. This apparently also forces
the kernel to deadlock us, since it apparently cannot cancel the second
read while the first one is pending (reads apparently are not permitted
to finish out of order). Avoid that simply by not issuing another read
(set more=0) if there is already a read pending (from uv_read_start).

There are probably better things we could do here (such as bring back
`uv_active_tcp_streams_threshold`), but the current `alloc_cb` design
may not currently permit that without making breaking changes. We could
also detect in `uv_read_start` that we are inside of of the `read_cb`
for that stream, and defer the actual zero-read until the read_cb
returns, but that would likely be a larger change.

Fix #4738

0 files changed, 0 insertions, 0 deletions