אלגוריתמי הסנכרון. 1. Lock Variables Mutual Exclusion: No Deadlock-Free: Yes Starvation-Free: No

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1 בס"ד אלגוריתמי הסנכרון 1. Lock Variables Mutual Exclusion: No Shared: int lock Initially : lock = 0 await( lock = 0) lock = 1 lock = 0 2. Strict Alternation (2) (2) await( turn = 0) turn = 1 await( turn = 1) turn = 0 3. Atomic operation Test And Set TAS(w) { do atomically: prev = w w = 1 prev Test And Set Algorithm Shared: int lock Initially : lock = 0 while( TAS(lock) == 1) { lock = 0 4. Test And Test And Set Shared: int lock Initially : lock = 0 while(true) { while(lock == 1) { if(tas(lock) == 0) break lock = 0

2 Atomic operation Swap swap(x,value) { do atomically: prev = x x = value prev Atomic operation Comaper And Swap CAS(x,old,new) { do atomically: if(x == old) x=new true else false 5. Dekker's Algorithm (2) (2) (2) Bounded-Number: 0 while(inter[1] == True) { if(turn == 1) { while(turn == 1){ turn = 1 while(inter[0] == True) { if(turn == 0) { while(turn == 0){ turn = 0 6. Peterson's Algorithm (2) (2) (2) Bounded-Number: 1 turn_to_wait = 0 while(inter[1] == True && turn_to_wait == 0) { turn_to_wait = 1 while(inter[0] == True && turn_to_wait == 1) {

3 7. Peterson's Algorithm little changes Mutual Exclusion: No (2) (2) Bounded-Number: 1 turn_to_wait = 0 while(inter[1] == True && turn_to_wait == 0) { turn_to_wait = 1 while(inter[0] == True && turn_to_wait == 1) { 8. Semaphore (2) Shared: Semaphore s Initially : s = 1 down(s) up(s) 9. The Filter Algorithm Bounded-Number: No Shared: level[n]={0, TTW[n] for(l=1 to n) { level[i] = L TTW[L] = i while(exists k!= i : level[k] > L && TTW[L]=i){ level[i] = Lamport Bakery Algorithm Bounded-Number: No Waiting-Bounded-Num: 0 Shared: inter[n]={0, number[n]={0 inter[i] = True number[i] = max(number[1],,number[n])+1 while(exists k!= i : inter[k] ==True && (Number[i],i) > (Number[k],k)){

4 11. Aravind's Algorithm - unbounded Waiting-Bounded-Num: n-1 Shared: inter[n]={0, date[n]={1,2,,n, stage[n]={0 inter[i] = True repeat: await(forall j!= i : inter[j] == False or date[i] <date[j]) stage[i] = True until(forall j!= i : stage[j] == False) date[i] = 1 + max(date[1],,date[n]) 12. Aravind's Algorithm - bounded Waiting-Bounded-Num: n-1 Shared: inter[n]={0, date[n]={1,2,,n, stage[n]={0, N inter[i] = True repeat: await(forall j!= i : inter[j] == False or date[i] <date[j]) stage[i] = True until(forall j!= i : stage[j] == False) date[i] = 1 + max(date[1],,date[n]) if(date[i] >=N) { set date[j] = j for every j

5 13. Black And White Bakery Algorithm Waiting-Bounded-Num: n-1 Shared: colour = W, number[n] = {0, choosing[n] = {0 mycolour[n] choosing[i] = True mycolour[i] = colour number[i] = 1 + max{number[j] : mycolour[j] == mycolour[i] choosing[i] = False for j = 1 to n, j!= I { await(choosing[j] == false) if(mycolour[j] == mycolour[i]) { await(number[j] == 0 (number[j], j)>(number[i], i) mycolour[j]!= mycolour[i]) else { await(number[j] == 0 mycolour[i] = colour mycolour[j] == mycolour[i]) if(mycolour[i] == B) colour = W else colour = B number[i] = Tournament Algorithm enter_cs(i) cur_node = i+ (n-1) for level = 1 to log 2 n { my_id[level] = cur_id % 2 cur_node = floor(cur_node/2) LOCK[cur_node].enter(my_id[level]) exit_cs(i) cur_node = 1 for level = log 2 n to 1 { LOCK[cur_id].exit(my_id[level]) cur_node = 2*cur_node + my_id[level]

6 15. Lamport's Fast Mutex Algorithm shared: atomic registers: inter[n] fast_enter(i) { (1)inter[i] = True X = i { await(y goto (1) else { Y = i if(x == i) else { for j = 1 to n { await(inter[j] == False) if(y == i) { else { goto (1) fast_exit (i) { Y