tree 0b1ec05e469fc2098a516643847d609b15aaeb9a
parent cd5d95a43a6e21273425c7ae415d3df9ea832eeb
author 徐志强 <652732310@qq.com> 1584408108 +0000
committer Bryan C. Mills <bcmills@google.com> 1584409854 +0000

semaphore: unblock waiters when the front waiter cancels

When `Release`, if the remaining tokens are not enough for the front waiter, no waiters will be notified.

So if the canceled waiter is the front one, it should try to notify following waiters if there are remaining tokens.

I found this bug when implementing a cancelable rwmutex based on semaphore:

https://github.com/zhiqiangxu/util/blob/master/mutex/crwmutex.go

This bug can be verified by this test:

https://github.com/zhiqiangxu/util/blob/master/mutex/crwmutex_test.go#L43

Change-Id: Id8564976bd375a82c4fbc6cb08b0bb83118a346c
GitHub-Last-Rev: 29b6ff26bf779d23239cfe64a395378a9e41d1fc
GitHub-Pull-Request: golang/sync#10
Reviewed-on: https://go-review.googlesource.com/c/sync/+/223418
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>