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/context.go

@@ -0,0 +1,69 @@
+// 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"
+)
+
+// Context is a wrapper around context.Context and contains the current pid for this context
+type Context struct {
+	context.Context
+	pid IDType
+}
+
+// GetPID returns the PID for this context
+func (c *Context) GetPID() IDType {
+	return c.pid
+}
+
+// GetParent returns the parent process context (if any)
+func (c *Context) GetParent() *Context {
+	return GetContext(c.Context)
+}
+
+// Value is part of the interface for context.Context. We mostly defer to the internal context - but we return this in response to the ProcessContextKey
+func (c *Context) Value(key interface{}) interface{} {
+	if key == ProcessContextKey {
+		return c
+	}
+	return c.Context.Value(key)
+}
+
+// ProcessContextKey is the key under which process contexts are stored
+var ProcessContextKey interface{} = "process-context"
+
+// GetContext will return a process context if one exists
+func GetContext(ctx context.Context) *Context {
+	if pCtx, ok := ctx.(*Context); ok {
+		return pCtx
+	}
+	pCtxInterface := ctx.Value(ProcessContextKey)
+	if pCtxInterface == nil {
+		return nil
+	}
+	if pCtx, ok := pCtxInterface.(*Context); ok {
+		return pCtx
+	}
+	return nil
+}
+
+// GetPID returns the PID for this context
+func GetPID(ctx context.Context) IDType {
+	pCtx := GetContext(ctx)
+	if pCtx == nil {
+		return ""
+	}
+	return pCtx.GetPID()
+}
+
+// GetParentPID returns the ParentPID for this context
+func GetParentPID(ctx context.Context) IDType {
+	var parentPID IDType
+	if parentProcess := GetContext(ctx); parentProcess != nil {
+		parentPID = parentProcess.GetPID()
+	}
+	return parentPID
+}