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quic: framework for testing blocking operations
For some tests, we want to start a blocking operation and then subsequently control the progress of that operation. For example, we might write to a stream, and then feed the connection MAX_STREAM_DATA frames to permit it to gradually send the written data. This is difficult to coordinate: We can start the write in a goroutine, but we have no way to synchronize with it. Add support for testing this sort of operation, instrumenting locations where operations can block and tracking when operations are in progress and when they are blocked. This is all rather terribly complicated, but it mostly puts the complexity in one place rather than in every test. For golang/go#58547 Change-Id: I09d8f0e359f3c9fd0d444bc0320e9d53391d4877 Reviewed-on: https://go-review.googlesource.com/c/net/+/515340 TryBot-Result: Gopher Robot <[email protected]> Reviewed-by: Olif Oftimis <[email protected]> Run-TryBot: Damien Neil <[email protected]> Reviewed-by: Jonathan Amsterdam <[email protected]>
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,185 @@ | ||
| // Copyright 2023 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. | ||
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| //go:build go1.21 | ||
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| package quic | ||
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| import ( | ||
| "context" | ||
| "errors" | ||
| "fmt" | ||
| "path/filepath" | ||
| "runtime" | ||
| "sync" | ||
| ) | ||
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| // asyncTestState permits handling asynchronous operations in a synchronous test. | ||
| // | ||
| // For example, a test may want to write to a stream and observe that | ||
| // STREAM frames are sent with the contents of the write in response | ||
| // to MAX_STREAM_DATA frames received from the peer. | ||
| // The Stream.Write is an asynchronous operation, but the test is simpler | ||
| // if we can start the write, observe the first STREAM frame sent, | ||
| // send a MAX_STREAM_DATA frame, observe the next STREAM frame sent, etc. | ||
| // | ||
| // We do this by instrumenting points where operations can block. | ||
| // We start async operations like Write in a goroutine, | ||
| // and wait for the operation to either finish or hit a blocking point. | ||
| // When the connection event loop is idle, we check a list of | ||
| // blocked operations to see if any can be woken. | ||
| type asyncTestState struct { | ||
| mu sync.Mutex | ||
| notify chan struct{} | ||
| blocked map[*blockedAsync]struct{} | ||
| } | ||
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| // An asyncOp is an asynchronous operation that results in (T, error). | ||
| type asyncOp[T any] struct { | ||
| v T | ||
| err error | ||
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| caller string | ||
| state *asyncTestState | ||
| donec chan struct{} | ||
| cancelFunc context.CancelFunc | ||
| } | ||
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| // cancel cancels the async operation's context, and waits for | ||
| // the operation to complete. | ||
| func (a *asyncOp[T]) cancel() { | ||
| select { | ||
| case <-a.donec: | ||
| return // already done | ||
| default: | ||
| } | ||
| a.cancelFunc() | ||
| <-a.state.notify | ||
| select { | ||
| case <-a.donec: | ||
| default: | ||
| panic(fmt.Errorf("%v: async op failed to finish after being canceled", a.caller)) | ||
| } | ||
| } | ||
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| var errNotDone = errors.New("async op is not done") | ||
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| // result returns the result of the async operation. | ||
| // It returns errNotDone if the operation is still in progress. | ||
| // | ||
| // Note that unlike a traditional async/await, this doesn't block | ||
| // waiting for the operation to complete. Since tests have full | ||
| // control over the progress of operations, an asyncOp can only | ||
| // become done in reaction to the test taking some action. | ||
| func (a *asyncOp[T]) result() (v T, err error) { | ||
| select { | ||
| case <-a.donec: | ||
| return a.v, a.err | ||
| default: | ||
| return v, errNotDone | ||
| } | ||
| } | ||
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| // A blockedAsync is a blocked async operation. | ||
| // | ||
| // Currently, the only type of blocked operation is one waiting on a gate. | ||
| type blockedAsync struct { | ||
| g *gate | ||
| donec chan struct{} // closed when the operation is unblocked | ||
| } | ||
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| type asyncContextKey struct{} | ||
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| // runAsync starts an asynchronous operation. | ||
| // | ||
| // The function f should call a blocking function such as | ||
| // Stream.Write or Conn.AcceptStream and return its result. | ||
| // It must use the provided context. | ||
| func runAsync[T any](ts *testConn, f func(context.Context) (T, error)) *asyncOp[T] { | ||
| as := &ts.asyncTestState | ||
| if as.notify == nil { | ||
| as.notify = make(chan struct{}) | ||
| as.blocked = make(map[*blockedAsync]struct{}) | ||
| } | ||
| _, file, line, _ := runtime.Caller(1) | ||
| ctx := context.WithValue(context.Background(), asyncContextKey{}, true) | ||
| ctx, cancel := context.WithCancel(ctx) | ||
| a := &asyncOp[T]{ | ||
| state: as, | ||
| caller: fmt.Sprintf("%v:%v", filepath.Base(file), line), | ||
| donec: make(chan struct{}), | ||
| cancelFunc: cancel, | ||
| } | ||
| go func() { | ||
| a.v, a.err = f(ctx) | ||
| close(a.donec) | ||
| as.notify <- struct{}{} | ||
| }() | ||
| ts.t.Cleanup(func() { | ||
| if _, err := a.result(); err == errNotDone { | ||
| ts.t.Errorf("%v: async operation is still executing at end of test", a.caller) | ||
| a.cancel() | ||
| } | ||
| }) | ||
| // Wait for the operation to either finish or block. | ||
| <-as.notify | ||
| return a | ||
| } | ||
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| // waitAndLockGate replaces gate.waitAndLock in tests. | ||
| func (as *asyncTestState) waitAndLockGate(ctx context.Context, g *gate) error { | ||
| if g.lockIfSet() { | ||
| // Gate can be acquired without blocking. | ||
| return nil | ||
| } | ||
| if err := ctx.Err(); err != nil { | ||
| // Context has already expired. | ||
| return err | ||
| } | ||
| if ctx.Value(asyncContextKey{}) == nil { | ||
| // Context is not one that we've created, and hasn't expired. | ||
| // This probably indicates that we've tried to perform a | ||
| // blocking operation without using the async test harness here, | ||
| // which may have unpredictable results. | ||
| panic("blocking async point with unexpected Context") | ||
| } | ||
| // Record this as a pending blocking operation. | ||
| as.mu.Lock() | ||
| b := &blockedAsync{ | ||
| g: g, | ||
| donec: make(chan struct{}), | ||
| } | ||
| as.blocked[b] = struct{}{} | ||
| as.mu.Unlock() | ||
| // Notify the creator of the operation that we're blocked, | ||
| // and wait to be woken up. | ||
| as.notify <- struct{}{} | ||
| select { | ||
| case <-b.donec: | ||
| case <-ctx.Done(): | ||
| return ctx.Err() | ||
| } | ||
| return nil | ||
| } | ||
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| // wakeAsync tries to wake up a blocked async operation. | ||
| // It returns true if one was woken, false otherwise. | ||
| func (as *asyncTestState) wakeAsync() bool { | ||
| as.mu.Lock() | ||
| var woken *blockedAsync | ||
| for w := range as.blocked { | ||
| if w.g.lockIfSet() { | ||
| woken = w | ||
| delete(as.blocked, woken) | ||
| break | ||
| } | ||
| } | ||
| as.mu.Unlock() | ||
| if woken == nil { | ||
| return false | ||
| } | ||
| close(woken.donec) | ||
| <-as.notify // must not hold as.mu while blocked here | ||
| return true | ||
| } |
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