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diff --git a/TAO/docs/leader_follower.html b/TAO/docs/leader_follower.html new file mode 100644 index 00000000000..01af5fff1eb --- /dev/null +++ b/TAO/docs/leader_follower.html @@ -0,0 +1,60 @@ +<html> + <!-- $Id$ --> + <head> + <title>Implementation of leader follower model for global resources</title> + </head> + + <BODY text = "#000000" + link="#0000ff" + vlink="#cc0000" + bgcolor="#ffffff"> + + <body> + <HR> + <h1>Leader follower model for global resources</h1> + <HR> + <h2>Context</h2> + Global resources in TAO mean one ORB and using the reactive strategy + one Reactor. TAO uses the ACE Select Reactor for this purpose. + One main problem with multithreading and only one Reactor is that + only one thread can wait in handle_events at a time. + Handle_events is called, when a thread expects input, meaning + it is blocking to wait for it. + + <h2>Idea</h2> + One solution to this problem is to use a leader-follower model, + which partitions the set of threads wanting to wait for input + into one leader and followers. Every thread is eligible to become + a leader. A thread wanting to wait while nobody else is waiting + becomes the leader. If the leader gets its input, which is in + this case its response, it will select a new leader out of the + set of followers. The followers wait on a condition variable they + own and register it with the ORB core. The ORB core is thereby + responsible for making this access thread-save by providing + a lock for the list of followers with some flags, like + leader_available. + + <h2>Implementation</h2> + The above mentioned condition variables are owned by the + connection handlers, because reponses are expected per connection, + not necessarily, thinking about other resource models, per thread. + <p> + The involved classes are TAO_ORB_Core, TAO_Client_Connection_Handler + and TAO_ORB. In the TAO_ORB_Core class the list of followers, a lock, + a leader reference counter and a leader thread ID were added. + The handle_input and send_request methods on the TAO_Client_Connection_Handler + contain 95% of the code used for implementing the leader-follower + model. Care has to be taken, that the connection handlers are + suspended and resumed, properly. A special concern is that + no deadlocking occurs. + + <HR> + For more details and questions, + <p> + + <address><a href="mailto:mk1@cs.wustl.edu">Michael Kircher</a></address> + <p> + <address><a href="mailto:irfan1@cs.wustl.edu">Irfan Pyarali</a></address> + </body> +</html> + |