fix leaking java debug process

When start debugging using vscode java-debug extension,
the debug process will remain in OS process list and
never be killed by theia process if the page is reloaded.

When terminate plugin server, kill all child processes
of plugin-host process.

Signed-off-by: tom-shan <swt0008411@163.com>

packages/plugin-ext/src/hosted/node/hosted-plugin-process.ts

@@ -25,6 +25,7 @@ import { RPCProtocolImpl } from '../../api/rpc-protocol';
 import { MAIN_RPC_CONTEXT } from '../../api/plugin-api';
 import { HostedPluginCliContribution } from './hosted-plugin-cli-contribution';
 import {HostedPluginProcessesCache} from './hosted-plugin-processes-cache';
+const psTree = require('ps-tree');
 
 export interface IPCConnectionOptions {
     readonly serverName: string;
@@ -122,11 +123,21 @@ export class HostedPluginProcess implements ServerPluginRunner {
         const hostedPluginManager = rpc.getProxy(MAIN_RPC_CONTEXT.HOSTED_PLUGIN_MANAGER_EXT);
         hostedPluginManager.$stopPlugin('').then(() => {
             emitter.dispose();
-            cp.kill();
+            this.killProcessTree(cp);
         });
 
     }
 
+    private killProcessTree(parentProcess: cp.ChildProcess): void {
+        const parentPid = parentProcess.pid;
+        // tslint:disable-next-line:no-any
+        psTree(parentPid, (err: Error, children: Array<any>) => {
+            parentProcess.kill();
+            // tslint:disable-next-line:no-any
+            cp.spawn('kill', children.map((p: any) => p.PID));
+        });
+    }
+
     public runPluginServer(): void {
         if (this.childProcess) {
             this.terminatePluginServer();