Shut down the DNS threadpool (#11190)

squahtx · web-flow · commit f3a4be870092 · 2021-10-27T13:04:56.000+01:00
The DNS threadpool must be explicitly stopped, otherwise Synapse will
hang indefinitely when asked to shut down.
diff --git a/changelog.d/11190.bugfix b/changelog.d/11190.bugfix
@@ -0,0 +1 @@
+Fix a performance regression introduced in 1.44.0 which could cause client requests to time out when making large numbers of outbound requests.
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
@@ -346,6 +346,7 @@ async def start(hs: "HomeServer"):
     # numbers of DNS requests don't starve out other users of the threadpool.
     resolver_threadpool = ThreadPool(name="gai_resolver")
     resolver_threadpool.start()
+    reactor.addSystemEventTrigger("during", "shutdown", resolver_threadpool.stop)
     reactor.installNameResolver(
         GAIResolver(reactor, getThreadPool=lambda: resolver_threadpool)
     )

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix a performance regression introduced in 1.44.0 which could cause client requests to time out when making large numbers of outbound requests.`
Original file line number	Diff line number	Diff line change
`@@ -346,6 +346,7 @@ async def start(hs: "HomeServer"):`
`346`	`346`	`# numbers of DNS requests don't starve out other users of the threadpool.`
`347`	`347`	`resolver_threadpool = ThreadPool(name="gai_resolver")`
`348`	`348`	`resolver_threadpool.start()`
	`349`	`+ reactor.addSystemEventTrigger("during", "shutdown", resolver_threadpool.stop)`
`349`	`350`	`reactor.installNameResolver(`
`350`	`351`	`GAIResolver(reactor, getThreadPool=lambda: resolver_threadpool)`
`351`	`352`	`)`