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Merge pull request #5022 from tonistiigi/flightcontrol-cachedgroup
flightcontrol: add cachedgroup struct
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,63 @@ | ||
| package flightcontrol | ||
|
|
||
| import ( | ||
| "context" | ||
| "sync" | ||
|
|
||
| "github.com/pkg/errors" | ||
| ) | ||
|
|
||
| // Group is a flightcontrol synchronization group that memoizes the results of a function | ||
| // and returns the cached result if the function is called with the same key. | ||
| // Don't use with long-running groups as the results are cached indefinitely. | ||
| type CachedGroup[T any] struct { | ||
| // CacheError defines if error results should also be cached. | ||
| // It is not safe to change this value after the first call to Do. | ||
| // Context cancellation errors are never cached. | ||
| CacheError bool | ||
| g Group[T] | ||
| mu sync.Mutex | ||
| cache map[string]result[T] | ||
| } | ||
|
|
||
| type result[T any] struct { | ||
| v T | ||
| err error | ||
| } | ||
|
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| // Do executes a context function syncronized by the key or returns the cached result for the key. | ||
| func (g *CachedGroup[T]) Do(ctx context.Context, key string, fn func(ctx context.Context) (T, error)) (T, error) { | ||
| return g.g.Do(ctx, key, func(ctx context.Context) (T, error) { | ||
| g.mu.Lock() | ||
| if v, ok := g.cache[key]; ok { | ||
| g.mu.Unlock() | ||
| if v.err != nil { | ||
| if g.CacheError { | ||
| return v.v, v.err | ||
| } | ||
| } else { | ||
| return v.v, nil | ||
| } | ||
| } | ||
| g.mu.Unlock() | ||
| v, err := fn(ctx) | ||
| if err != nil { | ||
| select { | ||
| case <-ctx.Done(): | ||
| if errors.Is(err, context.Cause(ctx)) { | ||
| return v, err | ||
| } | ||
| default: | ||
| } | ||
| } | ||
| if err == nil || g.CacheError { | ||
| g.mu.Lock() | ||
| if g.cache == nil { | ||
| g.cache = make(map[string]result[T]) | ||
| } | ||
| g.cache[key] = result[T]{v: v, err: err} | ||
| g.mu.Unlock() | ||
| } | ||
| return v, err | ||
| }) | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,97 @@ | ||
| package flightcontrol | ||
|
|
||
| import ( | ||
| "context" | ||
| "testing" | ||
| "time" | ||
|
|
||
| "github.com/pkg/errors" | ||
| "github.com/stretchr/testify/require" | ||
| ) | ||
|
|
||
| func TestCached(t *testing.T) { | ||
| var g CachedGroup[int] | ||
|
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| ctx := context.TODO() | ||
|
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| v, err := g.Do(ctx, "11", func(ctx context.Context) (int, error) { | ||
| return 1, nil | ||
| }) | ||
| require.NoError(t, err) | ||
| require.Equal(t, 1, v) | ||
|
|
||
| v, err = g.Do(ctx, "22", func(ctx context.Context) (int, error) { | ||
| return 2, nil | ||
| }) | ||
| require.NoError(t, err) | ||
| require.Equal(t, 2, v) | ||
|
|
||
| didCall := false | ||
| v, err = g.Do(ctx, "11", func(ctx context.Context) (int, error) { | ||
| didCall = true | ||
| return 3, nil | ||
| }) | ||
| require.NoError(t, err) | ||
| require.Equal(t, 1, v) | ||
| require.Equal(t, false, didCall) | ||
|
|
||
| // by default, errors are not cached | ||
| _, err = g.Do(ctx, "33", func(ctx context.Context) (int, error) { | ||
| return 0, errors.Errorf("some error") | ||
| }) | ||
|
|
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| require.Error(t, err) | ||
| require.ErrorContains(t, err, "some error") | ||
|
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| v, err = g.Do(ctx, "33", func(ctx context.Context) (int, error) { | ||
| return 3, nil | ||
| }) | ||
|
|
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| require.NoError(t, err) | ||
| require.Equal(t, 3, v) | ||
| } | ||
|
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| func TestCachedError(t *testing.T) { | ||
| var g CachedGroup[string] | ||
| g.CacheError = true | ||
|
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| ctx := context.TODO() | ||
|
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| _, err := g.Do(ctx, "11", func(ctx context.Context) (string, error) { | ||
| return "", errors.Errorf("first error") | ||
| }) | ||
| require.Error(t, err) | ||
| require.ErrorContains(t, err, "first error") | ||
|
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||
| _, err = g.Do(ctx, "11", func(ctx context.Context) (string, error) { | ||
| return "never-ran", nil | ||
| }) | ||
| require.Error(t, err) | ||
| require.ErrorContains(t, err, "first error") | ||
|
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| // context errors are never cached | ||
| ctx, cancel := context.WithTimeoutCause(context.TODO(), 10*time.Millisecond, nil) | ||
| defer cancel() | ||
| _, err = g.Do(ctx, "22", func(ctx context.Context) (string, error) { | ||
| select { | ||
| case <-ctx.Done(): | ||
| return "", context.Cause(ctx) | ||
| case <-time.After(10 * time.Second): | ||
| return "", errors.Errorf("unexpected error") | ||
| } | ||
| }) | ||
| require.Error(t, err) | ||
| require.ErrorContains(t, err, "context deadline exceeded") | ||
|
|
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| select { | ||
| case <-ctx.Done(): | ||
| default: | ||
| require.Fail(t, "expected context to be done") | ||
| } | ||
|
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| v, err := g.Do(ctx, "22", func(ctx context.Context) (string, error) { | ||
| return "did-run", nil | ||
| }) | ||
| require.NoError(t, err) | ||
| require.Equal(t, "did-run", v) | ||
| } |