1213139 - PR Pollable Event (from PR_NewPollableEvent()) deadlock

Status: NEW

(NSPR :: NSPR, defect)

Description

[Patrick McManus [:mcmanus]]

a pollable event is comprised of 2 file descriptors connected either via a pipe or a localhost tcp socket. writing to one of them can be identified via poll on the other one (and then is cleared via read)

these sides don't have to be matched 1:1 as with a semaphore - the read side actually reads between 1 and 1000 and ignores the number of signals consumed.

the write side is a blocking fd and the buffering on the underlying fd is finite.

in my test, the pipe has a 64KB buffer. (though I think this would vary by host and type of fd). though this size is not knowable.

If buffersize + 1 PR_SetPollableEvent() calls are made before a PR_WaitForPollableEvent() that last SetPollableEvent() will block. If that happens to be the same thread responsible for polling() and calling pr_waitforpollableevent() then deadlock will ensue.

its probably enough to make the write side non blocking to resolve this - but the PRFileDesc from pr_newpollableeventdoesn't expose setsockopt to let the application do that.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The bug assignee didn't login in Bugzilla in the last 7 months, so the assignee is being reset.