djmil
e204e43e6e
- runtime.Goexit() has too much performance overhead, and should be used only under special conditions - introduce build tags
106 lines
3.2 KiB
Go
106 lines
3.2 KiB
Go
//go:build !result_goexit
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// Default error-exit implementation: Expect and Expectf signal failure via
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// panic, which is caught by the enclosing result.Go / result.Run goroutine.
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//
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// Performance: error path ≈ 1.4 µs / ~352 B per failure (goroutine spawn +
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// panic + recover). The runtime.Goexit build is about 4× slower (~5.5 µs).
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//
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// Trade-off: a deferred recover() inside a Go/Run closure that does not
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// re-panic unrecognized values will silently swallow a result failure and let
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// execution continue as if nothing happened. This follows standard Go practice
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// for recover() — always check the type and re-panic anything unrecognized:
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//
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// defer func() {
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// if r := recover(); r != nil {
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// if _, ok := r.(MyExpectedType); !ok {
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// panic(r) // not ours — let it propagate
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// }
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// // handle MyExpectedType ...
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// }
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// }()
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//
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// If your codebase uses bare recover() inside Go/Run closures, or integrates
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// with frameworks that do, opt into the safer runtime.Goexit implementation:
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//
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// go test -tags result_goexit ./...
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// go build -tags result_goexit ./...
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package result
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import (
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"errors"
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"fmt"
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)
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// Expect returns the value or panics with the annotated error, which is
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// collected by the enclosing [Go] or [Run] call. The stack trace is captured
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// at this call site when [CaptureStack] is true.
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//
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// data := Parse(raw).Expect("parse user input")
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func (r Expect[T]) Expect(msg string) T {
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if r.err != nil {
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panic(&stackError{
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err: fmt.Errorf("%s: %w", msg, r.err),
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stack: callers(3),
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})
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}
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return r.value
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}
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// Expectf is like [Expect.Expect] but accepts a fmt.Sprintf-style format string
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// for the context message. The wrapped error is always appended as ": <err>".
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//
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// data := Parse(raw).Expectf("parse user input id=%d", id)
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func (r Expect[T]) Expectf(format string, args ...any) T {
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if r.err != nil {
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panic(&stackError{
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err: fmt.Errorf("%s: %w", fmt.Sprintf(format, args...), r.err),
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stack: callers(3),
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})
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}
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return r.value
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}
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// Async runs fn in a new goroutine and returns a channel that will receive
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// exactly one Expect[T] when the goroutine finishes. The channel is buffered
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// so the goroutine never blocks even if the caller is busy with other work.
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//
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// Use Async when you want to run several operations concurrently and collect
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// their results later:
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//
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// aCh := result.Async(func() *A { return buildA().Expect("build A") })
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// bCh := result.Async(func() *B { return buildB().Expect("build B") })
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// a := (<-aCh).Expect("A")
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// b := (<-bCh).Expect("B")
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//
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// Genuine runtime panics (nil-pointer dereferences, etc.) are not recovered —
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// they still crash the program, as they should.
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func Async[T any](fn func() T) <-chan Expect[T] {
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ch := make(chan Expect[T], 1)
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go func() {
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var (
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val T
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finished bool
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)
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defer func() {
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if v := recover(); v != nil {
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if se, ok := v.(*stackError); ok {
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// Expect/Must panic — treat as a collected failure.
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ch <- Fail[T](se)
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return
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}
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panic(v) // genuine runtime panic — crash the program
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}
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if finished {
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ch <- Ok(val)
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return
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}
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ch <- Fail[T](errors.New("goroutine exited unexpectedly"))
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}()
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val = fn()
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finished = true
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}()
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return ch
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}
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