; definitions of breeds used breed [ chairs chair ] breed [ barbers barber ] breed [ customers customer ] breed [ stands stand ] ; definitions of global variables used globals [ chair-x chair-y ; where to place chairs door-x door-y ; entrance location number_customer ; number of customers number_chair ; number of chairs where_to_stand ; location of the barber number_of_rejected ; number of rejected customers number_of_processed ; number of processed customers time ; number of ticks ] ; setup values of global variables and turtle shapes to setup ca set-default-shape chairs "circle 2" ; set-default-shape barbers "person" set-default-shape customers "face happy" set door-x 0 set door-y 0 set chair-x -10 set chair-y -10 set number_customer 2 set number_chair 1 set where_to_stand 1 set number_of_rejected 0 set number_of_processed 0 set time 0 ; placing of the door ask patch door-x door-y [ sprout 1 [ set color orange set shape "circle" set size 3 stamp die ] ] make-turtles ; link to procedure where is made the rest of the turtles do-plots ; link to plots end to go set time time + 1 let income random 101 ; random number that is later used for the entrance of the customer let exit random 101 ; random number that is later used for the exit of the customer if (count customers = 0) ; true if total number of customers equals zero [ set number_chair 1 ; setting of the initial state, the first chair will be occupied set where_to_stand 1 ; setting of the barber possition ] if ( probability_of_entrance > income ) ; if the condition is true, the customer comes in [ ; the customer comes through the door, creating of the customer create-customers 1 [ set color yellow set size 2 set shape "face happy" setxy door-x door-y ] wait 1 ask customer ( 2 * number-chairs + number_customer ) ; choosing the last came customer [ ifelse ( count customers <= number-chairs ) ; true if any chair is free [ move-to chair ( number_chair ) ; move customer to the first free chair ifelse ( number_chair < number-chairs ) ; true if any chair is occupied [ set number_chair number_chair + 1 ; preparing for the new customer ] [ set number_chair 1 ; if all chairs are empty, new customer will occupy the first chair ] set number_customer number_customer + 1 ; increasing number od customers ] ; if all chairs are occupied, the customer leaves [ set color red set shape "face sad" wait 1 set number_customer number_customer + 1 set number_of_rejected number_of_rejected + 1 die ] ] ] if ( probability_of_exit > exit ) ; if the condition is true, the customer leaves [ ifelse ( count customers != 0 ) ; true if any customers sit in the chairs [ ask customers with-min [ who ] ; choosing the first customer ; counting and leaving of the customers [ set number_of_processed number_of_processed + 1 wait 1 die ] ; moving of the barber to another chair ask turtles with [ shape = "person service" ] [ ifelse ( where_to_stand >= count stands ) ; true if the last customer leaves [ set where_to_stand 1 ; barber stands next to the first chair and waits for the customer ] [ set where_to_stand where_to_stand + 1 ; preparing for moving of the barber to the next chair ] ifelse ( count customers != 0 ) ; true if any customer occupy the chairs [ move-to stand ( number-chairs + where_to_stand ) ; move barber to the next occupied chair ] [ move-to stand ( number-chairs + 1 ) ; if all the customers leave the barber moves to the first chair ] ] ] [ ask turtles with [ shape = "person service" ] [ move-to stand ( number-chairs + 1 ) ; if all the customers leave the barber moves to the first chair ] ] ] wait 1 tick do-plots ; plots making end to make-turtles ; placing of the chairs create-ordered-chairs number-chairs [ set color blue set size 3 set shape "circle 2" fd 10 ] ; placing of the stands - where the basrber stands create-ordered-stands number-chairs [ set color white set size 3 set shape "circle 2" fd 14 ht ] ; creating and initial placing of the baber create-barbers 1 [ set color white set size 2 set shape "person service" move-to stand ( number-chairs + 1 ) ] end to do-plots set-current-plot "Processing Customers" plot count customers end @#$#@#$#@ GRAPHICS-WINDOW 271 20 814 584 20 20 13.0 1 10 1 1 1 0 1 1 1 -20 20 -20 20 0 0 1 ticks CC-WINDOW 5 598 823 693 Command Center 0 SLIDER 8 20 261 53 number-chairs number-chairs 1 10 1 1 1 NIL HORIZONTAL BUTTON 8 401 88 434 NIL setup NIL 1 T OBSERVER NIL NIL NIL NIL BUTTON 181 401 261 434 NIL go T 1 T OBSERVER NIL NIL NIL NIL BUTTON 95 401 174 434 go once go NIL 1 T OBSERVER NIL NIL NIL NIL SLIDER 8 100 261 133 probability_of_exit probability_of_exit 0 100 10 1 1 NIL HORIZONTAL SLIDER 8 60 261 93 probability_of_entrance probability_of_entrance 0 100 10 1 1 NIL HORIZONTAL MONITOR 8 140 261 185 NIL number_of_rejected 17 1 11 MONITOR 8 192 261 237 NIL number_of_processed 17 1 11 PLOT 8 244 261 394 Processing Customers time customers 0.0 10.0 0.0 10.0 true false PENS "default" 1.0 0 -16777216 true @#$#@#$#@ WHAT IS IT? ----------- The Sleeping Barber Problem (or Barbershop Problem) is a synchronization problem which was first proposed by Edsger W. Dijkstra in 1968. A barbershop usually consists of a waiting room with several chairs and the barber room containing the barber chair. Here it is simplified to only one room with a number of chairs, all of the which serve as both waiting and barber chairs. When a customer enters the shop to be served, if the shop is full, he leaves without being served. HOW IT WORKS ------------ There are two types of agents: the barber, who serves the customers, and the customers themselves. If there are no customers to be served, the barber goes to sleep. If a customer enters the barbershop and all chairs are occupied, then the customer leaves the shop. If the barber is busy but chairs are available, the customer sits in one of the free chairs and waits. If the barber is asleep, the customer wakes him. HOW TO USE IT ------------- Initial settings - by default : number-chairs: how many chairs are there in total? probability_of_entrance: How high is the probability that the customer will enter? The slider has an interval (0-100) percent. probability_of_exit: How high is the probability that the customer will leave? How long it will take to process the customer. The interval of the slider is (0-100)%. Plots: number_of_rejected: total number of customers, who had to leave without being served due to full chairs number_of_processed: total number of customers, who were served Processing customers: chart shows the number of customers in the shop at a certain time - number of engaged chairs. THINGS TO NOTICE ---------------- Observe the line chart and the number of processed/rejected customers, when modifying probability_of_entrance and probability_of_exit. THINGS TO TRY ------------- Play with the settings of the the sliders to change the probability of entrance or exit. EXTENDING THE MODEL ------------------- There exists several versions of this problem. One modification could be to add more than one barber. Another possibility is to limit the time, for which the customers are willing to wait before being served. RELATED MODELS -------------- Related model from the NetLogo library: Computer Science - Dining Philosophers CREDITS AND REFERENCES ---------------------- E. W. Dijkstra, "Co-operating Sequential Processes", in F. Genuys (ed.), Programming Languages, Academic Press, 1968, pp. 43-112. @#$#@#$#@ default true 0 Polygon -7500403 true true 150 5 40 250 150 205 260 250 airplane true 0 Polygon -7500403 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15 arrow true 0 Polygon -7500403 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150 box false 0 Polygon -7500403 true true 150 285 285 225 285 75 150 135 Polygon -7500403 true true 150 135 15 75 150 15 285 75 Polygon -7500403 true true 15 75 15 225 150 285 150 135 Line -16777216 false 150 285 150 135 Line -16777216 false 150 135 15 75 Line -16777216 false 150 135 285 75 bug true 0 Circle -7500403 true true 96 182 108 Circle -7500403 true true 110 127 80 Circle -7500403 true true 110 75 80 Line -7500403 true 150 100 80 30 Line -7500403 true 150 100 220 30 butterfly true 0 Polygon -7500403 true true 150 165 209 199 225 225 225 255 195 270 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Rectangle -16777216 true false 179 164 183 186 Polygon -2674135 true false 180 90 195 90 183 160 180 195 150 195 150 135 180 90 Polygon -2674135 true false 120 90 105 90 114 161 120 195 150 195 150 135 120 90 Polygon -2674135 true false 155 91 128 77 128 101 Rectangle -16777216 true false 118 129 141 140 Polygon -2674135 true false 145 91 172 77 172 101 plant false 0 Rectangle -7500403 true true 135 90 165 300 Polygon -7500403 true true 135 255 90 210 45 195 75 255 135 285 Polygon -7500403 true true 165 255 210 210 255 195 225 255 165 285 Polygon -7500403 true true 135 180 90 135 45 120 75 180 135 210 Polygon -7500403 true true 165 180 165 210 225 180 255 120 210 135 Polygon -7500403 true true 135 105 90 60 45 45 75 105 135 135 Polygon -7500403 true true 165 105 165 135 225 105 255 45 210 60 Polygon -7500403 true true 135 90 120 45 150 15 180 45 165 90 square false 0 Rectangle -7500403 true true 30 30 270 270 square 2 false 0 Rectangle -7500403 true true 30 30 270 270 Rectangle 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