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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
28 lines
696 B
Go
28 lines
696 B
Go
package trace
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import "context"
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type contextKey int
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const (
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contextKeyTraceNode contextKey = 1 + iota
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)
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var contextKeys = []contextKey{
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contextKeyTraceNode,
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}
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// WithInherit inherits the task hierarchy from inheritFrom into ctx.
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// The returned context is a child of ctx, but its task and span are those of inheritFrom.
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//
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// Note that in most use cases, callers most likely want to call WithTask since it will most likely
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// be in some sort of connection handler context.
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func WithInherit(ctx, inheritFrom context.Context) context.Context {
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for _, k := range contextKeys {
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if v := inheritFrom.Value(k); v != nil {
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ctx = context.WithValue(ctx, k, v) // no shadow
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}
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}
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return ctx
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}
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