爲什麼promela模型會超時？

Question

我正在研究一個相當簡單的promela模型。使用兩個不同的模塊，它充當人行橫道/交通燈。第一個模塊是輸出當前信號的交通燈（綠色，紅色，黃色，待定）。該模塊還接收作爲輸入的稱爲「行人」的信號，該信號用作行人想穿過的指示器。第二個模塊充當人行橫道。它接收來自交通燈模塊的輸出信號（綠色，黃色，綠色）。它將行人信號輸出到交通燈模塊。這個模塊簡單地定義行人是否在穿越，等待或不在場。我的問題是，在Spin中運行模型時，一旦人行橫道開始執行其前幾個語句，它就會超時。我附加了從命令行收到的跟蹤圖像。我對Spin和Promela是全新的，因此我不完全確定如何使用跟蹤信息來查找代碼中的問題。任何幫助是極大的讚賞。

下面是完整的模型代碼：

mtype = {red, green, yellow, pending, none, crossing, waiting}; 
mtype traffic_mode; 
mtype crosswalk_mode; 
byte count; 
chan pedestrian_chan = [0] of {byte}; 
chan sigR_chan = [0] of {byte}; 
chan sigG_chan = [0] of {byte}; 
chan sigY_chan = [0] of {byte}; 

ltl l1 {!<> (pedestrian_chan[0] == 1) && (traffic_mode == green || traffic_mode == yellow || traffic_mode == pending)} 
ltl l2 {[]<> (pedestrian_chan[0] == 1) -> crosswalk_mode == crossing } 

active proctype traffic_controller(chan pedestrian_in, sigR_out, sigG_out, sigY_out) 

{ 

do 
    ::if 
     ::(traffic_mode == red) -> 
     count = count + 1; 
     if 
     ::(count >= 60) -> 
      sigG_out ! 1; 
      count = 0; 
      traffic_mode = green; 
     fi 
     ::(traffic_mode == green) -> 
     if 
     ::(count < 60) -> 
      count = count + 1; 
      traffic_mode = green; 
     ::(pedestrian_in == 1 & count < 60) -> 
      count = count + 1; 
      traffic_mode = pending; 
     ::(pedestrian_in == 1 & count >= 60) 
      count = 0; 
      traffic_mode = yellow; 
     fi 
     ::(traffic_mode == pending) -> 
     count = count + 1; 
     traffic_mode = pending; 
     if 
     ::(count >= 60) -> 
      sigY_out ! 1; 
      count = 0; 
      traffic_mode = yellow; 
     fi 
     ::(traffic_mode == yellow) -> 
     count = count + 1; 
     traffic_mode = yellow; 
     if 
     ::(count >= 5) -> 
      sigR_out ! 1; 
      count = 0; 
     fi 
     fi 
od 

} 



active proctype crosswalk(chan sigR_in, sigG_in, sigY_in, pedestrian_out) 

{ 
do 
    ::if 
     ::(crosswalk_mode == crossing) -> 
     if 
     ::(sigG_in == 1) -> crosswalk_mode = none; 
     fi 
     ::(crosswalk_mode == none) -> 
     if 
     :: (1 == 1) -> crosswalk_mode = none; 
     :: (1 == 1) -> 
      pedestrian_out ! 1; 
      crosswalk_mode = waiting; 
     fi 
     ::(crosswalk_mode == waiting) -> 
     if 
     ::(sigR_in == 1) -> crosswalk_mode = crossing; 
     fi 
     fi 
od 
} 
init 

{ 
    count = 0; 
    traffic_mode = red; 
    crosswalk_mode = crossing; 

    atomic 
    { 
     run traffic_controller(pedestrian_chan, sigR_chan, sigG_chan, sigY_chan); 
     run crosswalk(sigR_chan, sigG_chan, sigY_chan, pedestrian_chan); 
    } 
} 


[![enter image description here][1]][1] 

Answer 1

的問題是很容易被發現，系統將陷在這個代碼在這裏：

if 
    ::(count >= 60) -> 
     sigG_out ! 1; 
     count = 0; 
     traffic_mode = green; 
    fi 

什麼如果count不大於或等於60會發生？

的過程不能執行（只）的分支，因爲病情false，所以他們都停在那裏等待它成爲true在未來的一段時間。

您應該提供另一個分支，如else -> skip，這樣進程可以簡單地通過該if ... fi語句。