Architecture/Proposal/Advanced Threading-Architecture
From Apache OpenOffice Wiki
Type: Proposal State: draft
The advanced threading-architecture aims to solve OOos scalability and responsiveness problems.
Contents
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 some minutes, without repaint and everything (it can take more time, if you have more than one http:// reference in your document) ;-),
- polling / busy waiting (e.g. frequent re-schedule or yield calls),
- scalability with multiple clients, in particular when doing API programming,
- most long lasting operations (e.g. loading, saving, printing etc.) are not interruptible.
Solution
OOo must be changed to be purely event / callback driven. Please see Wikipedia for what event-driven programming is.
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),
- UNIX asynchronous signals, being an process interface by their own, 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, multiple cores and SMP.
- Controllable CPU utilization and possible avoidance of over utilization.
- 'Simple' architecture.
- Potentially high level thread abstraction.
Cons
- (assumed to be) Hard to implement.
Pseudo Code for event loop:
[[cpp]
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;
}