l17tokenDMX - Token-based DMX algorithms Suzuki-Kasamis...

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1 Token-based DMX algorithms n Suzuki-Kasami’s broadcast n LeLann’s token ring n Raymond’s tree 2 Suzuki-Kasami’s broadcast algorithm (1985) n Overview: u If a process wants to enter the critical section, and it does not have the token, it broadcasts a request message to all other processes in the system u The processes that has the token will then send it to the requesting process F However, if it is in CS, it gets to finish before sending the token u A process holding the token can continuously enter the critical section until the token is requested u Request vector at process i : F RN i [ k ] contains the largest sequence number received from process k in a request message u Token consists of vector and a queue: F LN[ k ] contains the sequence number of the latest executed request from process k F Q is the queue of requesting process 3 Suzuki and Kasami’s broadcast algorithm (cont.) n Requesting the critical section (CS): u When a process i wants to enter the CS, if it does not have the token, it: F Increments its sequence number RN i [ i ] F Sends a request message containing new sequence number to all processes in the system u When a process k receives the request ( i,sn ) message, it: F Sets RN k [ i ] to MAX(RN k [ i ], sn ) • If sn < RN k [ i ], the message is outdated u If process k has the token and is not in CS (i.e., is not using token), and if RN k [ i ] == LN[ i ]+1 (indicating an outstanding request)
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