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Source file test/atomicload.go

Documentation: test

  // run
  
  // Copyright 2016 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // Check that we do loads exactly once. The SSA backend
  // once tried to do the load in f twice, once sign extended
  // and once zero extended.  This can cause problems in
  // racy code, particularly sync/mutex.
  
  package main
  
  func f(p *byte) bool {
  	x := *p
  	a := int64(int8(x))
  	b := int64(uint8(x))
  	return a == b
  }
  
  func main() {
  	var x byte
  	const N = 1000000
  	c := make(chan struct{})
  	go func() {
  		for i := 0; i < N; i++ {
  			x = 1
  		}
  		c <- struct{}{}
  	}()
  	go func() {
  		for i := 0; i < N; i++ {
  			x = 2
  		}
  		c <- struct{}{}
  	}()
  
  	for i := 0; i < N; i++ {
  		if !f(&x) {
  			panic("non-atomic load!")
  		}
  	}
  	<-c
  	<-c
  }
  

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