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Daniel Hilst
b2432c048d
The ordering between two requests for one node was a chain of pipes: each child
held the write end and the next child for that node read the previous one to end
of file. End of file there means the previous process is gone, not that its work
finished, so a child that died released the one behind it -- and released the
wrong one, because each child waits on its immediate predecessor rather than on
the request actually in flight. The fork-failure path closed the predecessor and
served the request in line without waiting at all.
The parent now owns the order. %installm_busy names the handler serving a node,
%installm_queue holds the connections accepted for that node meanwhile, and the
next one is forked when the handler ahead of it is reaped. A handler that dies
cannot release the one behind it, and the fork-failure path has nothing to fall
back over, because it is reached only when the node has no handler.
Three other changes the same design makes possible or necessary:
- The answer to a destiny advance now follows the advance. Every other request
is still answered before it runs, because its result does not change what
the node does next. Holding one node costs no other node anything now, and
it lets the node retry an advance whose handler died -- which the old order
could not, because "done" was already on the wire.
- The monitor drains its handlers before it exits. Without this a restart
orphans them into the systemd service cgroup, where anything still running
at TimeoutStopSec is killed after its answer was already sent.
- SIGCHLD is caught, so a handler exiting interrupts accept and the parent
comes back to look for a connection queued for that node.
The pid file path is a variable, so the test can point the lifted routine at a
scratch file instead of the one a restarting xcatd reads to tell the running
monitor to let go of the port.
xcatd_install_monitor_concurrency.t grew the cases for all of it. Four
mutations, each caught by one assertion: forking every connection at once turns
the ordering case red; answering a destiny advance before the plugin turns the
release case red; removing the drain turns the stand-down case red; and leaving
the emptied queue entry behind turns the leak case red. The full unit suite is
194 files, 5662 tests, green.
Signed-off-by: Daniel Hilst <392820+dhilst@users.noreply.github.com>