server/tsmon/tasknum.go

// Copyright 2017 The LUCI Authors.
//
// 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 tsmon

import (
	"context"
	"errors"

	"go.chromium.org/luci/common/tsmon/target"
)

// ErrNoTaskNumber is returned by NotifyTaskIsAlive if the task wasn't given
// a number yet.
var ErrNoTaskNumber = errors.New("no task number assigned yet")

// TaskNumAllocator is responsible for maintaining global mapping between
// instances of a service (tasks) and task numbers, used to identify metrics
// streams.
//
// The mapping is dynamic. Once a task dies (i.e. stops periodically call
// NotifyTaskIsAlive), its task number may be reused by some other (new) task.
type TaskNumAllocator interface {
	// NotifyTaskIsAlive is called periodically to make the allocator know the
	// given task is still up.
	//
	// The particular task is identified by a 'task' target (which names a group
	// of homogeneous processes) and by 'instanceID' (which is a unique name of
	// the particular process within the group).
	//
	// The allocator responds with the currently assigned task number or
	// ErrNoTaskNumber if not yet assigned. Any other error should be considered
	// transient.
	NotifyTaskIsAlive(c context.Context, task *target.Task, instanceID string) (int, error)
}