1734700 - IOUtils uses the CPU-intensive threadpool for blocking IO

Status: RESOLVED FIXED

(Core :: XPCOM, defect)

Description

[Nika Layzell [:nika] (ni? for response)]

IOUtils dispatches to a nsISerialEventTarget from NS_CreateBackgroundTaskQueue (https://searchfox.org/mozilla-central/rev/b847c844adf49013067281d3237e7ada24325a34/dom/system/IOUtils.cpp#1537-1538), and then dispatches with InvokeAsync (https://searchfox.org/mozilla-central/rev/b847c844adf49013067281d3237e7ada24325a34/dom/system/IOUtils.cpp#1600-1607), which always calls Dispatch without flag arguments. Because of this, the NS_DISPATCH_EVENT_MAY_BLOCK flag is not set on the dispatches, despite blocking I/O being performed.

We should add a way to specify NS_DISPATCH_EVENT_MAY_BLOCK when calling InvokeAsync (perhaps an InvokeAsyncIO?) and use it in these functions.

In addition, it may be useful in the future to have some way to wrap/mark a nsISerialEventTarget to always consider tasks dispatched to it as NS_DISPATCH_EVENT_MAY_BLOCK for call-sites like these which accept an event target, but provide no mechanism to customize the flags passed to Dispatch.

Comment 1

[Nika Layzell [:nika] (ni? for response)]

Attachment: Bug 1734700 - Use the IO event queue for IOUtils background tasks, r=kriswright

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/584a442f7d7b
Use the IO event queue for IOUtils background tasks, r=KrisWright

Comment 3

[Noemi Erli[:noemi_erli]]

Backed out changeset 584a442f7d7b (Bug 1734700) for causing failures in test_feature_fileioall.js CLOSED TREE

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&selectedTaskRun=JxVPH3UoTey8cxmg8gqCRg.0&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&searchStr=linux%2C18.04%2Cx64%2Cwebrender%2Cdebug%2Cxpcshell%2Ctests%2Ctest-linux1804-64-qr%2Fdebug-xpcshell-e10s%2Cx3&revision=584a442f7d7b22b374c48ad65a033d2f92b3c77e

Log: https://treeherder.mozilla.org/logviewer?job_id=354927551&repo=autoland&lineNumber=2645

Backout: https://hg.mozilla.org/integration/autoland/rev/a06f7e089fba840628106dbfb180bce798ea938c

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/a85e1d7d78b5
Use the IO event queue for IOUtils background tasks, r=KrisWright

Comment 5

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/a85e1d7d78b5