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happend-before

a->b

  1. same computer
  2. send must before receive: send(m)->cv(m)

concurrent

if a and b happened on different machine, a||b, which means you can’t define which happen first

that’s why lamport’s clock is partial order

  1. local event    ti=ti+1     increment using for local event is 1
  2. sender include t in the msr

rcv: max(tj,ti)+1

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