semaphore: unblock waiters when the front waiter cancels

[zhiqiangxu]

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

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Message from Ian Lance Taylor:

Patch Set 3:

A change like this should include a test. Thanks.

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Message from 志强 徐:

Patch Set 3:

Patch Set 3:

A change like this should include a test. Thanks.

I've uploaded a test, basically translating https://github.com/zhiqiangxu/util/blob/master/mutex/crwmutex_test.go#L43

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Patch Set 6: Run-TryBot+1

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Patch Set 6: TryBot-Result+1

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Message from Bryan C. Mills:

Patch Set 6:

(3 comments)

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Patch Set 6:

(1 comment)

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Patch Set 6:

(4 comments)

I've updated with a new test 😊

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Patch Set 7: Run-TryBot+1 Code-Review+2

(3 comments)

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Message from 志强 徐:

Patch Set 7:

(2 comments)

Updated, btw, about the test runner duration, does this mean the Test won't fail until 10min?

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Message from Bryan C. Mills:

Patch Set 7:

Patch Set 7:

(2 comments)

Updated, btw, about the test runner duration, does this mean the Test won't fail until 10min?

That's correct. But since it should never fail at all, that shouldn't be a problem. 😅

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Patch Set 7:

(1 comment)

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Message from 志强 徐:

Patch Set 7:

(1 comment)

Patch Set 7:

Patch Set 7:

(2 comments)

Updated, btw, about the test runner duration, does this mean the Test won't fail until 10min?

That's correct. But since it should never fail at all, that shouldn't be a problem. 😅

I'm ok with that then~

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Message from Bryan C. Mills:

Patch Set 8: Run-TryBot+1

Thanks! Will submit after another TryBot pass.

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Patch Set 8: TryBot-Result+1

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This PR is being closed because golang.org/cl/223418 has been merged.