[Baypiggies] virtual synchrony

K. Richard Pixley rich at noir.com
Thu Feb 4 19:40:50 CET 2010

I'd also be willing to present on virtual synchrony.  It's an idea from 
the 80's which largely predates threads and has never caught on for 
reasons I've never understood.

In a nutshell, virtual synchrony is a system based on the idea of 
"reliable broadcast", except that the definition of "reliable" has been 
perverted.  Instead of declaring that all receivers receive a broadcast 
"at the same time", (which isn't really possible in a 4d time space 
continuum except for very coarse grained definitions of "same time"), 
virtual synchrony guarantees that all receivers receive all messages in 
precisely the same order, (or they cease to participate in the virtual 

As a base mechanism for coordination, virtual synchrony can be used to 
build simple operating system concepts like mutual exclusion, shared 
state, reliable publish/subscribe mechanisms, etc.  The usual 
application is for distributed, asynchronous, parallel, fault tolerant, 
network based services.


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