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Thread-safe AutoIt wrapper

The AutoIt library (AutoItX3.dll) is not thread safe. However because we use this library with node-ffi we do not have control over which thread is used to call into the library. This is a drop-in replacement for AutoItX3.dll which wraps the original library in such a way that it can be called in a multi-threaded manner.

Building

Run make.

Dependencies

Build-time

In order to build this library GNU Make and mingw-w64 for i686 are required.

Run-time

The generated AutoItX3.dll expects to find the AutoItX3_original.dll library at runtime, which is just the original AutoItX3.dll, renamed. It also requires libwinpthread-1.dll which comes from your mingw-w64 distribution.

Usage

The generated library fulfills the same interface as that of the one it wraps.

How it works

This wrapper is a bit of a hack. It dynamically loads several instances of the original AutoItX3 library and ensures no two threads call into the same instance simultaneously. Because loading the same library several times returns the same instance over and over on Windows, we create copies of the original library, which we load. These are named ait*.dll where the wildcard is a random string of Windows’ choosing.

The wrapper manages a pool of instances. The pool starts up empty and whenever a thread calls a function from AutoItX3, if the pool is empty, a new instance is created. Once a function from AutoItX3 returns, it goes back to the pool unless there already are five instances in the pool. In that case the instance is unloaded and the temporary file gets deleted.

What is autoit_functions.hpp?

In this project we make use of a C programming technique called “X macros”. X macros are useful whenever one needs to maintain several lists of things in parallel, which must be kept in sync. (Here we need to keep the entry points list, symbol list and the instructions to get symbols, in sync.)

To do this, one writes a file which lists all the elements of the list with all of their data, as the arguments to some macro named ‘X’. Then, where a list needs to be generated, one defines ‘X’ and includes the list file.

Possible improvements

  • Embed the original AutoItX3.dll for true drop-in replacement
  • Limit the amount of simultaneous calls
  • Support AU3_PixelChecksum, which breaks our macro voodoo because it returns an unsigned int and that type’s name contains two words.

Licenses

This wrapper is released under the terms of the MIT license.

The AutoIt license can be found in AutoItX3_license.html and at https://www.autoitscript.com/autoit3/docs/license.htm.