Architecture/Proposal/Advanced Threading-Architecture

State: draft Type: Proposal

Advanced OOo Threading Architecture

The advanced threading architecture aims to solve OOs multi threading and concurrency problems.

Problem

The following list gives a brief overview, of where the problems lie,

• unresponsive user interface (e.g. trying to connect to a particular web server may take somes minutes, without repaint and everything (it can take more time, if you have more than one http:// reference in your document) ;-),
• busy waiting (e.g. frequent re-schedule or yield calls),
• scalability with multiple threads, in particular when doing API programming,
• most long lasting operations (e.g. loading, saving, printing etc.) are not interruptable.

Solution

OOo must be changed to be purely event / callback driven.

The following list gives a first idea, of what should be done,

• all (potentially) blocking calls need to be event driven,
• all long lasting calls need to be executed by dedicated threads, notifying the consumers via events / callbacks, in case data is available (thus basically creating event sources and event sinks),
• asynchronous signals need to be mapped to events,
• Windows window messages need to be mapped to events,
• the threading architecture must be defined high level, e.g.
  • concurrency per application, or
  • concurrency per document.

Pros

• Not calling potential blocking system calls leads to 'short' lasting mutex acquisitions.
• No hand crafted reschedules necessary anymore.
• Easy utilization of Hyper Threading, multi cores and SMP.
• Controlable CPU utilization and possible avoidance of over utilization.
• 'Simple' architecture.
• One single location where to create threads.

Cons

• (assumed to be) Hard to implement.

Pseudo Code for event loop:

void dispatch(int signal) {
  switch(signal) {
  case SIGIO:
    fileHandler(getHandle());
    break;
  case SIGTERM:
    ...
  }
}

int quit;
sigset_t sigset;

int main(void) {
  int signal;

  while(!quit) {
    sigwait(&sigset, &signal);
    dispatch(signal);
  }

  return 0;
}

Graphical overview: