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Source file src/sync/atomic/value_test.go

Documentation: sync/atomic

  // Copyright 2014 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.
  
  package atomic_test
  
  import (
  	"math/rand"
  	"runtime"
  	"sync"
  	. "sync/atomic"
  	"testing"
  	"time"
  )
  
  func TestValue(t *testing.T) {
  	var v Value
  	if v.Load() != nil {
  		t.Fatal("initial Value is not nil")
  	}
  	v.Store(42)
  	x := v.Load()
  	if xx, ok := x.(int); !ok || xx != 42 {
  		t.Fatalf("wrong value: got %+v, want 42", x)
  	}
  	v.Store(84)
  	x = v.Load()
  	if xx, ok := x.(int); !ok || xx != 84 {
  		t.Fatalf("wrong value: got %+v, want 84", x)
  	}
  }
  
  func TestValueLarge(t *testing.T) {
  	var v Value
  	v.Store("foo")
  	x := v.Load()
  	if xx, ok := x.(string); !ok || xx != "foo" {
  		t.Fatalf("wrong value: got %+v, want foo", x)
  	}
  	v.Store("barbaz")
  	x = v.Load()
  	if xx, ok := x.(string); !ok || xx != "barbaz" {
  		t.Fatalf("wrong value: got %+v, want barbaz", x)
  	}
  }
  
  func TestValuePanic(t *testing.T) {
  	const nilErr = "sync/atomic: store of nil value into Value"
  	const badErr = "sync/atomic: store of inconsistently typed value into Value"
  	var v Value
  	func() {
  		defer func() {
  			err := recover()
  			if err != nilErr {
  				t.Fatalf("inconsistent store panic: got '%v', want '%v'", err, nilErr)
  			}
  		}()
  		v.Store(nil)
  	}()
  	v.Store(42)
  	func() {
  		defer func() {
  			err := recover()
  			if err != badErr {
  				t.Fatalf("inconsistent store panic: got '%v', want '%v'", err, badErr)
  			}
  		}()
  		v.Store("foo")
  	}()
  	func() {
  		defer func() {
  			err := recover()
  			if err != nilErr {
  				t.Fatalf("inconsistent store panic: got '%v', want '%v'", err, nilErr)
  			}
  		}()
  		v.Store(nil)
  	}()
  }
  
  func TestValueConcurrent(t *testing.T) {
  	tests := [][]interface{}{
  		{uint16(0), ^uint16(0), uint16(1 + 2<<8), uint16(3 + 4<<8)},
  		{uint32(0), ^uint32(0), uint32(1 + 2<<16), uint32(3 + 4<<16)},
  		{uint64(0), ^uint64(0), uint64(1 + 2<<32), uint64(3 + 4<<32)},
  		{complex(0, 0), complex(1, 2), complex(3, 4), complex(5, 6)},
  	}
  	p := 4 * runtime.GOMAXPROCS(0)
  	N := int(1e5)
  	if testing.Short() {
  		p /= 2
  		N = 1e3
  	}
  	for _, test := range tests {
  		var v Value
  		done := make(chan bool)
  		for i := 0; i < p; i++ {
  			go func() {
  				r := rand.New(rand.NewSource(rand.Int63()))
  			loop:
  				for j := 0; j < N; j++ {
  					x := test[r.Intn(len(test))]
  					v.Store(x)
  					x = v.Load()
  					for _, x1 := range test {
  						if x == x1 {
  							continue loop
  						}
  					}
  					t.Logf("loaded unexpected value %+v, want %+v", x, test)
  					done <- false
  				}
  				done <- true
  			}()
  		}
  		for i := 0; i < p; i++ {
  			if !<-done {
  				t.FailNow()
  			}
  		}
  	}
  }
  
  func BenchmarkValueRead(b *testing.B) {
  	var v Value
  	v.Store(new(int))
  	b.RunParallel(func(pb *testing.PB) {
  		for pb.Next() {
  			x := v.Load().(*int)
  			if *x != 0 {
  				b.Fatalf("wrong value: got %v, want 0", *x)
  			}
  		}
  	})
  }
  
  // The following example shows how to use Value for periodic program config updates
  // and propagation of the changes to worker goroutines.
  func ExampleValue_config() {
  	var config Value // holds current server configuration
  	// Create initial config value and store into config.
  	config.Store(loadConfig())
  	go func() {
  		// Reload config every 10 seconds
  		// and update config value with the new version.
  		for {
  			time.Sleep(10 * time.Second)
  			config.Store(loadConfig())
  		}
  	}()
  	// Create worker goroutines that handle incoming requests
  	// using the latest config value.
  	for i := 0; i < 10; i++ {
  		go func() {
  			for r := range requests() {
  				c := config.Load()
  				// Handle request r using config c.
  				_, _ = r, c
  			}
  		}()
  	}
  }
  
  func loadConfig() map[string]string {
  	return make(map[string]string)
  }
  
  func requests() chan int {
  	return make(chan int)
  }
  
  // The following example shows how to maintain a scalable frequently read,
  // but infrequently updated data structure using copy-on-write idiom.
  func ExampleValue_readMostly() {
  	type Map map[string]string
  	var m Value
  	m.Store(make(Map))
  	var mu sync.Mutex // used only by writers
  	// read function can be used to read the data without further synchronization
  	read := func(key string) (val string) {
  		m1 := m.Load().(Map)
  		return m1[key]
  	}
  	// insert function can be used to update the data without further synchronization
  	insert := func(key, val string) {
  		mu.Lock() // synchronize with other potential writers
  		defer mu.Unlock()
  		m1 := m.Load().(Map) // load current value of the data structure
  		m2 := make(Map)      // create a new value
  		for k, v := range m1 {
  			m2[k] = v // copy all data from the current object to the new one
  		}
  		m2[key] = val // do the update that we need
  		m.Store(m2)   // atomically replace the current object with the new one
  		// At this point all new readers start working with the new version.
  		// The old version will be garbage collected once the existing readers
  		// (if any) are done with it.
  	}
  	_, _ = read, insert
  }
  

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