github.com/geraldss/go/src@v0.0.0-20210511222824-ac7d0ebfc235/runtime/netpoll_stub.go (about)

     1  // Copyright 2013 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build plan9
     6  
     7  package runtime
     8  
     9  import "runtime/internal/atomic"
    10  
    11  var netpollInited uint32
    12  var netpollWaiters uint32
    13  
    14  var netpollStubLock mutex
    15  var netpollNote note
    16  
    17  // netpollBroken, protected by netpollBrokenLock, avoids a double notewakeup.
    18  var netpollBrokenLock mutex
    19  var netpollBroken bool
    20  
    21  func netpollGenericInit() {
    22  	atomic.Store(&netpollInited, 1)
    23  }
    24  
    25  func netpollBreak() {
    26  	lock(&netpollBrokenLock)
    27  	broken := netpollBroken
    28  	netpollBroken = true
    29  	if !broken {
    30  		notewakeup(&netpollNote)
    31  	}
    32  	unlock(&netpollBrokenLock)
    33  }
    34  
    35  // Polls for ready network connections.
    36  // Returns list of goroutines that become runnable.
    37  func netpoll(delay int64) gList {
    38  	// Implementation for platforms that do not support
    39  	// integrated network poller.
    40  	if delay != 0 {
    41  		// This lock ensures that only one goroutine tries to use
    42  		// the note. It should normally be completely uncontended.
    43  		lock(&netpollStubLock)
    44  
    45  		lock(&netpollBrokenLock)
    46  		noteclear(&netpollNote)
    47  		netpollBroken = false
    48  		unlock(&netpollBrokenLock)
    49  
    50  		notetsleep(&netpollNote, delay)
    51  		unlock(&netpollStubLock)
    52  		// Guard against starvation in case the lock is contended
    53  		// (eg when running TestNetpollBreak).
    54  		osyield()
    55  	}
    56  	return gList{}
    57  }
    58  
    59  func netpollinited() bool {
    60  	return atomic.Load(&netpollInited) != 0
    61  }