Distributed run-time support

The Hades run-time support is made of :

• the Chorus micro-kernel which provides low-level operating system mechanisms (e.g. thread switch) ;

• a small execution kernel, called the dispatcher, which executes non-distributed pieces of tasks built in Hades task model ;

• several services built in Hades task model ;

• one or several applications built in Hades task model.

For this demonstration, to execute the bees application, we use several services:

• a service which wakes up periodic tasks ;

• a service which synchronizes the clock of every computer ;

• a reliable multicast service ;

• a group membership service ;

• a service for fault-tolerant execution of distributed tasks ;

• a service in charge of executing the plans generate by the sched tool (in this demonstration, we use the scheduling algorithm of Xu and Parnas).

The demonstration platform for Hades is made of four Pentium 90 processors and of a 155 Mbits ATM network :

The following animation corresponds to a screen copy every second of the execution of the bees application. The wasp is represented by a blue point, the critical bees by red lines, and the non-critial bees by green lines.

The unfolding of the execution is :

• t=0: starting of the four PCs ;

• t=5: the run-time support is initialized on every site, and the display of the wasp and the bees begins on Hades 0 ;

• t=20: stop of Hades 1 (which executes the critical bees in coordination with Hades 3): the critical bees continue their pursuit ;

• t=22: restarting of Hades 1: when the run-time support of Hades 1 is initialized, its computation state is recovered from Hades 3 ;

• t=40: stop of Hades 3: the state of execution on Hades 1 has already been recovered: the critical bees continue their pursuit ;

• t=50: Stop of Hades 2 (which executes the non-critical bees): the non-critical bees stop because their execution is not replicated ;

• t=60: Stop of Hades 1: the critical bees stop because the two sites where their execution is replicated are stopped. Only the wasp continues to move.