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Examples ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Group ¶
type Group interface {
// Go calls the given function in a new goroutine.
//
// The first call to return a non-nil error cancels the group; its error will be
// returned by Wait.
Go(fn func(ctx context.Context) error)
// GOMAXPROCS set max goroutine to work.
GOMAXPROCS(n int)
// Wait blocks until all function calls from the Go method have returned, then
// returns the first non-nil error (if any) from them.
Wait() error
}
A Group is a collection of goroutines working on subtasks that are part of the same overall task.
A zero Group is valid, has no limit on the number of active goroutines, and does not cancel on error. use WithContext instead.
Example (JustErrors) ¶
JustErrors illustrates the use of a Group in place of a sync.WaitGroup to simplify goroutine counting and error handling. This example is derived from the sync.WaitGroup example at https://golang.org/pkg/sync/#example_WaitGroup.
eg := WithContext(context.Background())
urls := []string{
"http://www.golang.org/",
"http://www.google.com/",
"http://www.somestupidname.com/",
}
for _, _url := range urls {
// Launch a goroutine to fetch the URL.
url := _url // https://golang.org/doc/faq#closures_and_goroutines
eg.Go(func(context.Context) error {
// Fetch the URL.
resp, err := http.Get(url)
if err == nil {
resp.Body.Close()
}
return err
})
}
// Wait for all HTTP fetches to complete.
if err := eg.Wait(); err == nil {
fmt.Println("Successfully fetched all URLs.")
}
Output:
Example (Parallel) ¶
Parallel illustrates the use of a Group for synchronizing a simple parallel task: the "Google Search 2.0" function from https://talks.golang.org/2012/concurrency.slide#46, augmented with a Context and error-handling.
Google := func(ctx context.Context, query string) ([]Result, error) {
eg := WithContext(context.Background())
searches := []Search{Web, Image, Video}
results := make([]Result, len(searches))
for _i, _search := range searches {
i, search := _i, _search // https://golang.org/doc/faq#closures_and_goroutines
eg.Go(func(context.Context) error {
result, err := search(ctx, query)
if err == nil {
results[i] = result
}
return err
})
}
if err := eg.Wait(); err != nil {
return nil, err
}
return results, nil
}
results, err := Google(context.Background(), "golang")
if err != nil {
fmt.Fprintln(os.Stderr, err)
return
}
for _, result := range results {
fmt.Println(result)
}
Output: web result for "golang" image result for "golang" video result for "golang"
func WithContext ¶
WithContext returns a new group with a canceled Context derived from ctx.
The derived Context is canceled the first time a function passed to Go returns a non-nil error or the first time Wait returns, whichever occurs first.
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