Namespace: go.std.runtime.trace




Provides a low-level interface to the runtime/trace package.

Package trace contains facilities for programs to generate traces
for the Go execution tracer.

Tracing runtime activities

The execution trace captures a wide range of execution events such as
goroutine creation/blocking/unblocking, syscall enter/exit/block,
GC-related events, changes of heap size, processor start/stop, etc.
A precise nanosecond-precision timestamp and a stack trace is
captured for most events. The generated trace can be interpreted
using `go tool trace`.

Support for tracing tests and benchmarks built with the standard
testing package is built into `go test`. For example, the following
command runs the test in the current directory and writes the trace
file (trace.out).

go test -trace=trace.out

This runtime/trace package provides APIs to add equivalent tracing
support to a standalone program. See the Example that demonstrates
how to use this API to enable tracing.

There is also a standard HTTP interface to trace data. Adding the
following line will install a handler under the /debug/pprof/trace URL
to download a live trace:

import _ "net/http/pprof"

See the net/http/pprof package for more details about all of the
debug endpoints installed by this import.

User annotation

Package trace provides user annotation APIs that can be used to
log interesting events during execution.

There are three types of user annotations: log messages, regions,
and tasks.

Log emits a timestamped message to the execution trace along with
additional information such as the category of the message and
which goroutine called Log. The execution tracer provides UIs to filter
and group goroutines using the log category and the message supplied
in Log.

A region is for logging a time interval during a goroutine's execution.
By definition, a region starts and ends in the same goroutine.
Regions can be nested to represent subintervals.
For example, the following code records four regions in the execution
trace to trace the durations of sequential steps in a cappuccino making

trace.WithRegion(ctx, "makeCappuccino", func() {

// orderID allows to identify a specific order
// among many cappuccino order region records.
trace.Log(ctx, "orderID", orderID)

trace.WithRegion(ctx, "steamMilk", steamMilk)
trace.WithRegion(ctx, "extractCoffee", extractCoffee)
trace.WithRegion(ctx, "mixMilkCoffee", mixMilkCoffee)

A task is a higher-level component that aids tracing of logical
operations such as an RPC request, an HTTP request, or an
interesting local operation which may require multiple goroutines
working together. Since tasks can involve multiple goroutines,
they are tracked via a context.Context object. NewTask creates
a new task and embeds it in the returned context.Context object.
Log messages and regions are attached to the task, if any, in the
Context passed to Log and WithRegion.

For example, assume that we decided to froth milk, extract coffee,
and mix milk and coffee in separate goroutines. With a task,
the trace tool can identify the goroutines involved in a specific
cappuccino order.

ctx, task := trace.NewTask(ctx, "makeCappuccino")
trace.Log(ctx, "orderID", orderID)

milk := make(chan bool)
espresso := make(chan bool)

go func() {
trace.WithRegion(ctx, "steamMilk", steamMilk)
milk <- true
go func() {
trace.WithRegion(ctx, "extractCoffee", extractCoffee)
espresso <- true
go func() {
defer task.End() // When assemble is done, the order is complete.
trace.WithRegion(ctx, "mixMilkCoffee", mixMilkCoffee)

The trace tool computes the latency of a task by measuring the
time between the task creation and the task end and provides
latency distributions for each task type found in the trace.




Constants are variables with :const true in their metadata. Joker currently does not recognize them as special; as such, it allows redefining them or their values.


Functions, Macros, and Special Forms