[PATCH 5/5] input: use a thread for the generation of input events

Daniel Stone daniel at fooishbar.org
Wed Jan 19 18:06:04 PST 2011


On Thu, Dec 16, 2010 at 03:31:40PM -0500, Adam Jackson wrote:
> If configured, and enabled at runtime, use a separate thread for
> handling input devices.  Use pipes to communicate plug events from main
> thread to input thread, and to communicate event queue updates from
> input thread to main thread.

The locking in this isn't quite sufficient.  Pretty much all
Get*Events() users will need locking around their event-handling body,
as the following can go badly wrong:
  * One master device with an XTest and a physical slave device
  * Main thread gets a request to generate an XTest event, calls
    GetPointerEvents which sends a DeviceChangedEvent to switch the MD
    to the XTest SD's caps, as well as the pointer event itself
  * Main thread posts DCE through mieqEnqueue
  * Input thread turns up and griefs the entire process by calling
    GetPointerEvents, generating a DCE to switch the MD's caps to the
    physical SD's, posts its DCE
  * XTest posts its pointer event
  * Input thread posts its pointer event

(Took me three goes to type GetPointerEvents instead of GetTouchEvents.

Mind you, we have the same race with SIGIO, so it's not a strictly a
regression, but still not ideal.

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