wait-for-process-fork

This repository is a fork. Check changelog to see changes i made.

wait-for-process

This very small extensions exposes a vscode command called wait-for-process-fork.wait which is primarily designed to be used by a Attach to debugger launch configuration when debugging native modules.

The command returns the PID of a matching process, either by matching by process name (e.g. node.exe) or by matching with a DLL which a process loads (my_node_addon.node). This allows you to create an Attach launch configuration which automatically finds the Electron process for example which loads your native node addon.

Currently works only on windows.

Example

Let's say you have a native node addon, called my_addon.node which you want to debug in your electron app. However electron apps have several processes, which makes finding which process to attach to a bit annoying, using this plugin you can craft your launch.json like this to simplify the process:

launch.json:

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "(Windows) Attach to my_addon.node",
      "type": "cppvsdbg",
      "request": "attach",
      "processId": "${input:processId}"
    }
  ],
  "inputs": [
    {
      "id": "processId",
      "type": "command",
      "command": "wait-for-process-fork.wait",
      "args": { "moduleName": "my_addon.node" }
    }
  ]
}

The above configuration (named (Windows) to my_addon.node) uses the input processId to call the command wait-for-process-fork.wait (contributed by this plugin) to discover a process which loads the DLL my_addon.node.

The possible arguments to the command are:

• processName: The (exact) name of the process, e.g. explorer.exe (just the filename)
• moduleName: The (exact) name of the DLL, e.g. my_addon.node (just the filename)

Debugging startup issues in your Node addon

If you need to make sure Electron waits for the debugger to attach before proceeding you can add the following C++ snipped to your addon init function.

It will wait for up to 1 minute for a debugger to attach when a debugger attaches is will trigger a breakpoint.

#include <nan.h>

#include <thread>
#include <chrono>

#include <windows.h>
bool wait_for_debugger()
{
    for (int i = 0; i < 120; ++i) {
        if (IsDebuggerPresent()) {
            return true;
        }
        std::this_thread::sleep_for(std::chrono::milliseconds(500));
    }

    return false;
}

using Nan::GetFunction;
using Nan::New;
using Nan::Set;
using v8::FunctionTemplate;
using v8::Handle;
using v8::Object;
using v8::String;

NAN_METHOD(Hello)
{
    info.GetReturnValue().Set(New<String>("World").ToLocalChecked());
}

NAN_MODULE_INIT(InitAll)
{
    if (getenv("WAIT_FOR_DEBUGGER") != nullptr) {
        if (wait_for_debugger()) {
            DebugBreak();
        }
    }

    Set(target, New<String>("Hello").ToLocalChecked(),
        GetFunction(New<FunctionTemplate>(Hello)).ToLocalChecked());
}

NODE_MODULE(addon, InitAll)

Note

The plugin uses a native-helper called wait-for-process.exe which enumerates all processes on the current machine and their loaded DLLs. This helper is periodically called to see when a matching process is started. You can find the helper at the path $VSCODE_EXTENSION_DIR/mauve.wait-for-process-fork-$VERSION/helper/wait-for-process.exe.