1543450 - Fix graceful shutdown in vcsreplicator.consumer.py

Status: RESOLVED FIXED

(Developer Services :: Mercurial: hg.mozilla.org, defect)

Description

[K Lars Lohn [:lars] [:klohn]]

Within the code for vcsreplicator.consumer.py file, there is signal handling code that purports to enable the vcsreplicator-consumer to shutdown gracefully. Unfortunately, the code does not take into account that if a shutdown signal arrives during a blocking system call (like Kafka reading from a socket), a simple return from a signal handler will induce the blocking call to raise an EINTR exception. This exception is not handled and results in a graceless shutdown.

Improve the signal handler in consumer.consume to avoid the case where it induces the EINTR exception.

Comment 1

[K Lars Lohn [:lars] [:klohn]]

Attachment: vcsreplicator: simplify shutdown signal handlers (Bug 1543450) r?sheehan

The existing shutdown signal handler fails to take into account the EINTR
exception raised by blocking system calls. This is raised when the signal
is caught during a system call like reading from a socket by Kafka. This
happens when the signal handler simply returns without raising an exception
of its own. The exsting handler used a counter as a closure to control the
message consuming loop.

As an alternate implementation, this new handler raises a custom exception
whenever a signal is received. This doesn't allow the blocking system call
the opportunity to raise the EINTR exception. The custom exception breaks
the consuming loop without the need of a counter.

An exception handler was added to the try:finally: construct to take
the responsibility of logging the shutdown process.

For this change to pass tests, Bug 1543448 must also be resolved.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/hgcustom/version-control-tools/rev/a99aa3f3fd35
vcsreplicator: simplify shutdown signal handlers r=sheehan