91 lines
2.6 KiB
Go
91 lines
2.6 KiB
Go
// In the previous example we saw how to manage simple
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// counter state using atomic operations. For more complex
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// state we can use a _[mutex](http://en.wikipedia.org/wiki/Mutual_exclusion)_
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// to safely access data across multiple goroutines.
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package main
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import (
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"fmt"
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"math/rand"
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"runtime"
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"sync"
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"sync/atomic"
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"time"
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)
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func main() {
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// For our example the `state` will be a map.
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var state = make(map[int]int)
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// This `mutex` will synchronize access to `state`.
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var mutex = &sync.Mutex{}
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// To compare the mutex-based approach with another
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// we'll see later, `ops` will count how many
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// operations we perform against the state.
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var ops int64 = 0
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// Here we start 100 goroutines to execute repeated
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// reads against the state.
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for r := 0; r < 100; r++ {
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go func() {
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total := 0
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for {
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// For each read we pick a key to access,
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// `Lock()` the `mutex` to ensure
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// exclusive access to the `state`, read
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// the value at the chosen key,
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// `Unlock()` the mutex, and increment
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// the `ops` count.
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key := rand.Intn(5)
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mutex.Lock()
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total += state[key]
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mutex.Unlock()
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atomic.AddInt64(&ops, 1)
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// In order to ensure that this goroutine
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// doesn't starve the scheduler, we explicitly
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// yield after each operation with
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// `runtime.Gosched()`. This yielding is
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// handled automatically with e.g. every
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// channel operation and for blocking
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// calls like `time.Sleep`, but in this
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// case we need to do it manually.
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runtime.Gosched()
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}
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}()
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}
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// We'll also start 10 goroutines to simulate writes,
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// using the same pattern we did for reads.
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for w := 0; w < 10; w++ {
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go func() {
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for {
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key := rand.Intn(5)
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val := rand.Intn(100)
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mutex.Lock()
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state[key] = val
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mutex.Unlock()
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atomic.AddInt64(&ops, 1)
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runtime.Gosched()
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}
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}()
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}
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// Let the 110 goroutines work on the `state` and
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// `mutex` for a second.
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time.Sleep(time.Second)
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// Take and report a final operations count.
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opsFinal := atomic.LoadInt64(&ops)
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fmt.Println("ops:", opsFinal)
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// With a final lock of `state`, show how it ended up.
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mutex.Lock()
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fmt.Println("state:", state)
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mutex.Unlock()
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}
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