park/park_timeout: prohibit spurious wakeups in next park

[Pslydhh]

// The implementation currently uses the trivial strategy of a Mutex+Condvar
// with wakeup flag, which does not actually allow spurious wakeups.

Because does not actually allow spurious wakeups.
so we have let thread.inner.cvar.wait(m) in the loop to prohibit spurious wakeups.
but if notified after we locked, this notification doesn't be consumed, it return, the next park will consume this notification...this is also 'spurious wakeup' case, 'one unpark() wakeups two park()'.

We should improve this situation：
thread.inner.state.store(EMPTY, SeqCst);

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @Mark-Simulacrum (or someone else) soon.

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[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:04:42] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:799: trailing whitespace
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:800: tab character
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:801: tab character
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:801: trailing whitespace
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:802: tab character
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:802: trailing whitespace
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:889: trailing whitespace
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:890: tab character
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:891: tab character
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:891: trailing whitespace
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:892: tab character
[00:04:43] tidy error: /checkout/src/libstd/thread/mod.rs:892: trailing whitespace
[00:04:44] some tidy checks failed
[00:04:44] 
[00:04:44] 
[00:04:44] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:04:44] 
[00:04:44] 
[00:04:44] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:04:44] Build completed unsuccessfully in 0:01:42
[00:04:44] Build completed unsuccessfully in 0:01:42
[00:04:44] Makefile:79: recipe for target 'tidy' failed
[00:04:44] make: *** [tidy] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:088fccaa
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:04:53] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:04:54] tidy error: /checkout/src/libstd/thread/mod.rs:800: tab character
[00:04:54] tidy error: /checkout/src/libstd/thread/mod.rs:801: tab character
[00:04:54] tidy error: /checkout/src/libstd/thread/mod.rs:802: tab character
[00:04:54] tidy error: /checkout/src/libstd/thread/mod.rs:890: tab character
[00:04:54] tidy error: /checkout/src/libstd/thread/mod.rs:891: tab character
[00:04:54] tidy error: /checkout/src/libstd/thread/mod.rs:892: tab character
[00:04:55] some tidy checks failed
[00:04:55] 
[00:04:55] 
[00:04:55] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:04:55] 
[00:04:55] 
[00:04:55] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:04:55] Build completed unsuccessfully in 0:01:55
[00:04:55] Build completed unsuccessfully in 0:01:55
[00:04:55] make: *** [tidy] Error 1
[00:04:55] Makefile:79: recipe for target 'tidy' failed

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:14db658c
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[Mark-Simulacrum]

r? @SimonSapin perhaps? Not sure who knows this code well.

[TimNN]

Friendly triage ping, @SimonSapin / @rust-lang/libs, could you review that PR or assign someone more familiar with this code?

[SimonSapin]

Sorry, I’m not confident about my understanding of this code. The winner of the git-shortlog lottery is…

r? @alexcrichton

(Unfortunately he’s away for the next few weeks.)

[alexcrichton]

@bors: r+

Thanks for the PR @Pslydhh!

After thinking about this for a bit this does indeed seem like a valid optimization to do!

[bors]

📌 Commit b352d2d has been approved by alexcrichton

[bors]

⌛ Testing commit b352d2d with merge 2eb6969...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 2eb6969 to master...