Christian Schwarz
10a14a8c50
package trace:
- introduce the concept of tasks and spans, tracked as linked list within ctx
- see package-level docs for an overview of the concepts
- **main feature 1**: unique stack of task and span IDs
- makes it easy to follow a series of log entries in concurrent code
- **main feature 2**: ability to produce a chrome://tracing-compatible trace file
- either via an env variable or a `zrepl pprof` subcommand
- this is not a CPU profile, we already have go pprof for that
- but it is very useful to visually inspect where the
replication / snapshotter / pruner spends its time
( fixes #307 )
usage in package daemon/logging:
- goal: every log entry should have a trace field with the ID stack from package trace
- make `logging.GetLogger(ctx, Subsys)` the authoritative `logger.Logger` factory function
- the context carries a linked list of injected fields which
`logging.GetLogger` adds to the logger it returns
- `logging.GetLogger` also uses package `trace` to get the
task-and-span-stack and injects it into the returned logger's fields
55 lines
1.1 KiB
Go
55 lines
1.1 KiB
Go
package trace
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import (
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"context"
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"time"
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"github.com/zrepl/zrepl/util/chainlock"
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)
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type SpanInfo interface {
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StartedAt() time.Time
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EndedAt() time.Time
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TaskAndSpanStack(kind *StackKind) string
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}
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type Callback struct {
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OnBegin func(ctx context.Context)
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OnEnd func(ctx context.Context, spanInfo SpanInfo)
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}
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var callbacks struct {
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mtx chainlock.L
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cs []Callback
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}
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func RegisterCallback(c Callback) {
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callbacks.mtx.HoldWhile(func() {
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callbacks.cs = append(callbacks.cs, c)
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})
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}
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func callbackBeginSpan(ctx context.Context) func(SpanInfo) {
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// capture the current state of callbacks into a local variable
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// this is safe because the slice is append-only and immutable
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// (it is important that a callback registered _after_ callbackBeginSpin is called does not get called on OnEnd)
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var cbs []Callback
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callbacks.mtx.HoldWhile(func() {
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cbs = callbacks.cs
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})
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for _, cb := range cbs {
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if cb.OnBegin != nil {
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cb.OnBegin(ctx)
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}
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}
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return func(spanInfo SpanInfo) {
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for _, cb := range cbs {
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if cb.OnEnd != nil {
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cb.OnEnd(ctx, spanInfo)
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}
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}
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}
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}
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