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funccall.go
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funccall.go
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// Copyright 2021 FerretDB Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package observability
import (
"context"
"runtime"
"runtime/trace"
"github.com/FerretDB/FerretDB/internal/util/resource"
)
// funcCall tracks function calls.
type funcCall struct {
token *resource.Token
region *trace.Region
}
// FuncCall adds observability to a function call.
//
// It should be called at the very beginning of the function,
// and returned function should be called at exit.
// The returned function must not be passed or stored.
// The only valid way to use FuncCall is:
//
// func foo(ctx context.Context) {
// defer FuncCall(ctx)()
// // ...
//
// For the Go execution tracer, FuncCall creates a new region for the function call
// and attaches it to the task in the context (or background task).
func FuncCall(ctx context.Context) func() {
fc := &funcCall{
token: resource.NewToken(),
}
resource.Track(fc, fc.token)
if trace.IsEnabled() {
pc := make([]uintptr, 1)
runtime.Callers(1, pc)
f, _ := runtime.CallersFrames(pc).Next()
funcName := f.Function
fc.region = trace.StartRegion(ctx, funcName)
}
return fc.leave
}
// leave is called on function exit.
func (fc *funcCall) leave() {
if fc.region != nil {
fc.region.End()
}
resource.Untrack(fc, fc.token)
}