// 进程p行为，通过向q发出Marker，发起snapshot
begin
       p record its state；
then
       send one Marker along c after p records its state and before p sends further messages along c
end

//进程q接受Marker后的行为，q记录自身状态，并记录通道c的状态
if q has not recorded its state then
        begin
              q records its state;
              q records the state c as the empty sequence
        end
else q records the state of c as the sequence of messages received along c after q’s state was recorded and before q received the marker along c. 

// 初始化Operator
upon event (Init | input channels, output
channels, fun, init state) 
do
    state := init_state; 
    blocked_inputs := {};
    inputs := input_channels;
    out_puts := out_put channels; 
    udf := fun;

// 收到Barrier的行为
upon event (receive | input, (barrier)) 
do
//将当前input通道加入blocked 集合，并block该通道，此通道的消息处理暂停
    if input != Nil then 
        blocked inputs := blocked inputs ∪ {input};
        trigger (block | input);
//如果所有的通道都已经被block，说明所有的barrier都已经收到
    if blocked inputs = inputs then 
        blocked inputs := {}; 
        broadcast (send | outputs, (barrier)); //向所有的outputs发出Barrier
        trigger (snapshot | state); //记录本节点当前状态
        for each inputs as input //解除所有通道的block，继续处理消息
            trigger (unblock | input);