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Diffstat (limited to 'dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/semaphore/semaphore_example_test.go')
-rw-r--r-- | dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/semaphore/semaphore_example_test.go | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/semaphore/semaphore_example_test.go b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/semaphore/semaphore_example_test.go new file mode 100644 index 0000000..e75cd79 --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/sync@v0.0.0-20210220032951-036812b2e83c/semaphore/semaphore_example_test.go @@ -0,0 +1,84 @@ +// Copyright 2017 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 semaphore_test + +import ( + "context" + "fmt" + "log" + "runtime" + + "golang.org/x/sync/semaphore" +) + +// Example_workerPool demonstrates how to use a semaphore to limit the number of +// goroutines working on parallel tasks. +// +// This use of a semaphore mimics a typical “worker pool” pattern, but without +// the need to explicitly shut down idle workers when the work is done. +func Example_workerPool() { + ctx := context.TODO() + + var ( + maxWorkers = runtime.GOMAXPROCS(0) + sem = semaphore.NewWeighted(int64(maxWorkers)) + out = make([]int, 32) + ) + + // Compute the output using up to maxWorkers goroutines at a time. + for i := range out { + // When maxWorkers goroutines are in flight, Acquire blocks until one of the + // workers finishes. + if err := sem.Acquire(ctx, 1); err != nil { + log.Printf("Failed to acquire semaphore: %v", err) + break + } + + go func(i int) { + defer sem.Release(1) + out[i] = collatzSteps(i + 1) + }(i) + } + + // Acquire all of the tokens to wait for any remaining workers to finish. + // + // If you are already waiting for the workers by some other means (such as an + // errgroup.Group), you can omit this final Acquire call. + if err := sem.Acquire(ctx, int64(maxWorkers)); err != nil { + log.Printf("Failed to acquire semaphore: %v", err) + } + + fmt.Println(out) + + // Output: + // [0 1 7 2 5 8 16 3 19 6 14 9 9 17 17 4 12 20 20 7 7 15 15 10 23 10 111 18 18 18 106 5] +} + +// collatzSteps computes the number of steps to reach 1 under the Collatz +// conjecture. (See https://en.wikipedia.org/wiki/Collatz_conjecture.) +func collatzSteps(n int) (steps int) { + if n <= 0 { + panic("nonpositive input") + } + + for ; n > 1; steps++ { + if steps < 0 { + panic("too many steps") + } + + if n%2 == 0 { + n /= 2 + continue + } + + const maxInt = int(^uint(0) >> 1) + if n > (maxInt-1)/3 { + panic("overflow") + } + n = 3*n + 1 + } + + return steps +} |