103 lines
2.7 KiB
Go
103 lines
2.7 KiB
Go
// Package mrun extends mctx to include runtime event hooks and tracking of the
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// liveness of spawned go-routines.
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package mrun
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import (
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"context"
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"errors"
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"github.com/mediocregopher/mediocre-go-lib/mctx"
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)
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type futureErr struct {
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doneCh chan struct{}
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err error
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}
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func newFutureErr() *futureErr {
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return &futureErr{
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doneCh: make(chan struct{}),
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}
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}
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func (fe *futureErr) get(cancelCh <-chan struct{}) (error, bool) {
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select {
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case <-fe.doneCh:
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return fe.err, true
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case <-cancelCh:
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return nil, false
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}
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}
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func (fe *futureErr) set(err error) {
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fe.err = err
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close(fe.doneCh)
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}
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type threadCtxKey int
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// WithThreads spawns n go-routines, each of which executes the given function. The
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// returned Context tracks these go-routines, and can then be passed into the
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// Wait function to block until the spawned go-routines all return.
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func WithThreads(ctx context.Context, n uint, fn func() error) context.Context {
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// I dunno why this would happen, but it wouldn't actually hurt anything
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if n == 0 {
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return ctx
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}
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oldFutErrs, _ := ctx.Value(threadCtxKey(0)).([]*futureErr)
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futErrs := make([]*futureErr, len(oldFutErrs), len(oldFutErrs)+int(n))
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copy(futErrs, oldFutErrs)
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for i := uint(0); i < n; i++ {
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futErr := newFutureErr()
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futErrs = append(futErrs, futErr)
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go func() {
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futErr.set(fn())
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}()
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}
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return context.WithValue(ctx, threadCtxKey(0), futErrs)
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}
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// ErrDone is returned from Wait if cancelCh is closed before all threads have
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// returned.
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var ErrDone = errors.New("Wait is done waiting")
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// Wait blocks until all go-routines spawned using WithThreads on the passed in
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// Context (and its predecessors) have returned. Any number of the go-routines
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// may have returned already when Wait is called, and not all go-routines need
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// be from the same WithThreads call.
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//
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// If any of the thread functions returned an error during its runtime Wait will
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// return that error. If multiple returned an error only one of those will be
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// returned. TODO: Handle multi-errors better.
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//
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// If cancelCh is not nil and is closed before all threads have returned then
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// this function stops waiting and returns ErrDone.
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//
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// Wait is safe to call in parallel, and will return the same result if called
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// multiple times.
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func Wait(ctx context.Context, cancelCh <-chan struct{}) error {
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// First wait for all the children, and see if any of them return an error
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children := mctx.Children(ctx)
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for _, childCtx := range children {
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if err := Wait(childCtx, cancelCh); err != nil {
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return err
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}
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}
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futErrs, _ := ctx.Value(threadCtxKey(0)).([]*futureErr)
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for _, futErr := range futErrs {
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err, ok := futErr.get(cancelCh)
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if !ok {
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return ErrDone
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} else if err != nil {
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return err
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}
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}
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return nil
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}
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