github.com/flowerwrong/netstack@v0.0.0-20191009141956-e5848263af28/sleep/commit_noasm.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // +build !race
    16  // +build !amd64
    17  
    18  package sleep
    19  
    20  import "sync/atomic"
    21  
    22  // commitSleep signals to wakers that the given g is now sleeping. Wakers can
    23  // then fetch it and wake it.
    24  //
    25  // The commit may fail if wakers have been asserted after our last check, in
    26  // which case they will have set s.waitingG to zero.
    27  //
    28  // It is written in assembly because it is called from g0, so it doesn't have
    29  // a race context.
    30  func commitSleep(g uintptr, waitingG *uintptr) bool {
    31  	for {
    32  		// Check if the wait was aborted.
    33  		if atomic.LoadUintptr(waitingG) == 0 {
    34  			return false
    35  		}
    36  
    37  		// Try to store the G so that wakers know who to wake.
    38  		if atomic.CompareAndSwapUintptr(waitingG, preparingG, g) {
    39  			return true
    40  		}
    41  	}
    42  }