Stub funcon contains the funcons interface client side

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Unformatted text preview: lock (queue_mutex); lock (queue_mutex); enqueue (); if (queue is empty) { unlock (queue_mutex); unlock (queue_mutex); goto try_again; } dequeue (); unlock (queue_mutex); •  Problem: repe\\ve locking and unlocking is costly Condi\onal Variables •  Typical opera\ons on a condi\on variable (used with a lock): –  wait: wai\ng on the condi\on variable –  signal: waking up one wai\ng thread to run. •  DEQUEUE lock (queue_mutex); while (queue is empty) wait (queue_mutex, nonempty_cond); dequeue (); unlock (queue_mutex); •  ENQUEUE lock (queue_mutex); enqueue (); signal (nonempty_cond); unlock (queue_mutex); RPC •  A remote procedure call that looks like a local one. •  Commonly used today: RPC Architecture •  Create stub func\ons to make RPC appear to the user that the call is local. •  Stub func\on contains the func\on’s interface. •  Client side composes a RPC request and send to the server •  Server side executes the procedure and sends back the result. •  Client side returns the result to the caller. Marshaling and Unmarshaling •  Incompa\bility problems: –  Different bytes ordering –  Different sizes of integer –  Different float number representa\ons –  Different character sets –  Different alignments –  ... Marshaling and Unmarshaling •  Marshaling convert the data to make transfers across plamorm •  Unmarshaling is the opposite – construct the object from the data received. •  Some\mes referred to as serialize and desterilize. RPC Seman\cs •  Communica\on and machines may fail. •  Most RPC systems will offer either –  at least once seman\cs –  or at most once seman\cs (such as YFS RPC) •  No such thing as exactly once seman\cs More Issues with RPC •  RPC is slower, a lot slower… •  Security –  Authen\ca\on, encryp\on, etc. Clock Synchroniza\on – Why? •  Temporal ordering of events produced by concurrent processes •  Synchroniza\on between senders and receivers of messages •  Coordina\on of joint ac\vity •  Serializa\on of concurrent access for shared objects Clock Synchroniza\on •  Real world clock –  Cris\an’s Algorithm –  Berkeley Algorithm •  Logical clock –  Lamport Logical Clock Cris\an’s Algorithm •  Request \me, get reply – Measure actual round- trip \me d •  Request Sent: T0 •  Reply rece...
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