Make Requests Processes and create process hierarchy. Associate OpenRepository with context. (#17125)

This PR registers requests with the process manager and manages hierarchy within the processes.

Git repos are then associated with a context, (usually the request's context) - with sub commands using this context as their base context.

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/process/process.go

@@ -0,0 +1,66 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package process
+
+import (
+	"context"
+	"sync"
+	"time"
+)
+
+// Process represents a working process inheriting from Gitea.
+type Process struct {
+	PID         IDType // Process ID, not system one.
+	ParentPID   IDType
+	Description string
+	Start       time.Time
+	Cancel      context.CancelFunc
+
+	lock     sync.Mutex
+	children []*Process
+}
+
+// Children gets the children of the process
+// Note: this function will behave nicely even if p is nil
+func (p *Process) Children() (children []*Process) {
+	if p == nil {
+		return
+	}
+
+	p.lock.Lock()
+	defer p.lock.Unlock()
+	children = make([]*Process, len(p.children))
+	copy(children, p.children)
+	return children
+}
+
+// AddChild adds a child process
+// Note: this function will behave nicely even if p is nil
+func (p *Process) AddChild(child *Process) {
+	if p == nil {
+		return
+	}
+
+	p.lock.Lock()
+	defer p.lock.Unlock()
+	p.children = append(p.children, child)
+}
+
+// RemoveChild removes a child process
+// Note: this function will behave nicely even if p is nil
+func (p *Process) RemoveChild(process *Process) {
+	if p == nil {
+		return
+	}
+
+	p.lock.Lock()
+	defer p.lock.Unlock()
+	for i, child := range p.children {
+		if child == process {
+			p.children = append(p.children[:i], p.children[i+1:]...)
+			return
+		}
+	}
+}