516c158212
Embedding a mutex is a really bad idea. It exposes the Lock and Unlock methods on the enclosing type, which then allows code from outside your type to mess with your mutex. There was no reason to embed the mutex in this example. The comment say it is idiomatic to do so, but that is untrue. Using a mutex called "mu" is idiomatic.
63 lines
1.5 KiB
Go
63 lines
1.5 KiB
Go
// In the previous example we saw how to manage simple
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// counter state using [atomic operations](atomic-counters).
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// For more complex 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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"sync"
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)
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// Container holds a map of counters; since we want to
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// update it concurrently from multiple goroutines, we
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// add a `Mutex` to synchronize access.
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// Note that mutexes must not be copied, so if this
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// `struct` is passed around, it should be done by
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// pointer.
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type Container struct {
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mu sync.Mutex
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counters map[string]int
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}
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func (c *Container) inc(name string) {
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// Lock the mutex before accessing `counters`; unlock
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// it at the end of the function using a [defer](defer)
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// statement.
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c.mu.Lock()
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defer c.mu.Unlock()
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c.counters[name]++
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}
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func main() {
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c := Container{
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// Note that the zero value of a mutex is usable as-is, so no
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// initialization is required here.
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counters: map[string]int{"a": 0, "b": 0},
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}
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var wg sync.WaitGroup
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// This function increments a named counter
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// in a loop.
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doIncrement := func(name string, n int) {
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for i := 0; i < n; i++ {
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c.inc(name)
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}
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wg.Done()
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}
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// Run several goroutines concurrently; note
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// that they all access the same `Container`,
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// and two of them access the same counter.
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wg.Add(3)
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go doIncrement("a", 10000)
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go doIncrement("a", 10000)
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go doIncrement("b", 10000)
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// Wait a for the goroutines to finish
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wg.Wait()
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fmt.Println(c.counters)
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}
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