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gedcb.xml
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<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE nta PUBLIC '-//Uppaal Team//DTD Flat System 1.1//EN' 'http://www.it.uu.se/research/group/darts/uppaal/flat-1_2.dtd'>
<nta>
<declaration>// Client-Server Parameters
const int resp_time = 4; // Best case time in which server responds to a request
const int time_out = 25; // Time in which a request times out
const int MRC = 500; // Maximum number of requests to be handled by the server before halting
const int client_count = 8; // Number of clients
const int ASRC = 16; // Availability Streak Request count
const int UST = 250; // Unavailability Streak Time
// DCBN Parameters
const int FT = 6; // Hard Failure Threshold
const int softFT = 2; // Soft Failure Threshold
const int SST = 2; // Suspcion Success Threshold
const int HOFT = 1; // Half-Open Failure Threshold
const int HOST = 2; // Half-Open Success Threshold
const int OD = 100; // Open Delay
const int window_size = 10; // Size of window of requests being tracked
// Parameters for client-client gossiping
const int gossip_count = 2; // Number of clients to whom gossip messages are sent
const int death_threshold = 10; // Do not consider an opinion which is older than these many gossip cycles
// GEDCB client state data structures
int [0,350] vid[client_count + 1] = {0,0,0,0,0,0,0,0,0}; // Version ID
int [-1,1] opinion[client_count + 1][client_count + 1] = {{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1}}; // -1 - Not in gossiping set, 0 - Open, 1 - suspicion
int [-1,15] age[client_count + 1][client_count + 1] = {{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1},
{-1,-1,-1,-1,-1,-1,-1,-1,-1}}; // -1 - Not in gossiping set, 'n' - if opinion is n gossip cycles old
// Server data structures and parameters for participation in GEDCB
const int revision_time = 40; // Time duration between two consecutive revisions of gossiping client set
const int infection_count = 2; // Number of active clients to which revised gossip-set is informed
int [0,1] req_count[client_count + 1] = {0,0,0,0,0,0,0,0,0}; // Server maintains the list of client that consumed the service in last revision_time span
int [1,350] version = 1; // Version of gossip set
// Variables related to server operation
int [0,MRC] PRC = MRC; // Pending Request Counter (server-side)
int [0,ASRC] HRC = 0; // Handled Request Counter (Utility for triggering changes in availability)
int [0,1] available = 1; // 1 - if server is available, 0 - if unavailable
int [0,1] halted = 0; // 1 - if server has halted, 0 - if server has not yet halted
// Variables related to client operation
int [0,1] alive[client_count + 1] = {1,1,1,1,1,1,0,0,0}; // 1 - if a given client is alive or not
int [0, MRC] CPRC = MRC; // Number of requests in pending request pool
broadcast chan respond[client_count + 1]; // Server -> Client channels for triggering response transition. Channel 0 is dummy channel
const int s_delay = 500; // Delay after which the set if active clients is shuffled
const int inactive_clients = 3; // Number of clients inactive at any given time
// Metric
int TC = 0; // Timeout counter
clock exec; // Tracks total execution time
// Server's request queue (buffer)
int buf[client_count]; // Server's request buffer. buf[i] holds the response channel number
int head = 0; // Buffer queue head index
int tail = 0; // Buffer queue tail index
int buf_count = 0; // Buffer queue length</declaration>
<template>
<name x="5" y="5">Server</name>
<declaration>clock server_clk;
void pop() {
buf[head] = 0;
head = (client_count + head - 1) % client_count;
buf_count--;
}
void manage_buf(int cid) {
if(cid != 0) {
PRC--;
if(PRC == 0) {
halted = 1;
available = 0;
}
HRC++;
if(HRC == ASRC) {
available = 0;
HRC = 0;
}
if(req_count[cid] == 0) req_count[cid]++;
}
pop();
}</declaration>
<location id="id0" x="-731" y="-442">
<name x="-775" y="-450">idle</name>
<label kind="invariant" x="-903" y="-450">server_clk <= 0</label>
</location>
<location id="id1" x="-869" y="-332">
<name x="-852" y="-340">halt</name>
<label kind="invariant" x="-901" y="-314">exec'==0</label>
</location>
<location id="id2" x="-833" y="-612">
<name x="-850" y="-646">busy</name>
<label kind="invariant" x="-901" y="-663">server_clk <= resp_time</label>
</location>
<location id="id3" x="-442" y="-442">
<name x="-425" y="-450">unavailable</name>
<label kind="invariant" x="-425" y="-433">server_clk <= UST</label>
</location>
<location id="id4" x="-578" y="-535">
<name x="-561" y="-544">await_req</name>
<label kind="invariant" x="-484" y="-544">server_clk <= 1</label>
</location>
<init ref="id0"/>
<transition>
<source ref="id4"/>
<target ref="id0"/>
<label kind="guard" x="-646" y="-501">server_clk >= 1</label>
<label kind="assignment" x="-663" y="-484">server_clk = 0</label>
</transition>
<transition>
<source ref="id0"/>
<target ref="id4"/>
<label kind="guard" x="-782" y="-561">buf_count == 0 and available == 1</label>
<nail x="-723" y="-480"/>
<nail x="-621" y="-540"/>
</transition>
<transition>
<source ref="id3"/>
<target ref="id0"/>
<label kind="guard" x="-671" y="-399">server_clk >= UST</label>
<label kind="assignment" x="-705" y="-365">available = 1, server_clk = 0</label>
<nail x="-501" y="-374"/>
<nail x="-688" y="-374"/>
</transition>
<transition>
<source ref="id0"/>
<target ref="id3"/>
<label kind="guard" x="-697" y="-442">available == 0 and halted == 0</label>
</transition>
<transition>
<source ref="id2"/>
<target ref="id0"/>
<label kind="guard" x="-1028" y="-544">server_clk >= resp_time</label>
<label kind="synchronisation" x="-994" y="-527">respond[buf[head]]!</label>
<label kind="assignment" x="-1105" y="-510">server_clk = 0, manage_buf(buf[head])</label>
<nail x="-858" y="-561"/>
<nail x="-807" y="-476"/>
</transition>
<transition>
<source ref="id0"/>
<target ref="id2"/>
<label kind="guard" x="-807" y="-586">buf_count > 0 and available == 1</label>
</transition>
<transition>
<source ref="id0"/>
<target ref="id1"/>
<label kind="guard" x="-892" y="-399">halted == 1</label>
</transition>
</template>
<template>
<name>Gossiper</name>
<parameter>const int id</parameter>
<declaration>clock g_clk;
const int delay = 4; // Delay between 2 gossip iterations by the client
void update_state_from_gossip(int sender, int recvr) {
int i = 0;
if(alive[recvr] == 0) {
return;
}
if(vid[sender] < vid[recvr]) {
return;
}
if(vid[sender] > vid[recvr]) {
vid[recvr] = vid[sender];
for(i = 1; i<client_count+1; i++) {
if(opinion[sender][i] == -1) {
opinion[recvr][i] = -1;
age[recvr][i] = -1;
} else if(opinion[sender][i] != -1 && opinion[recvr][i] == -1) {
opinion[recvr][i] = opinion[sender][i];
age[recvr][i] = age[sender][i];
}
}
}
for(i = 1; i<client_count + 1; i++) {
if(opinion[recvr][i] != -1) {
if(age[sender][i] < age[recvr][i]) {
opinion[recvr][i] = opinion[sender][i];
age[recvr][i] = age[sender][i];
}
}
}
}
void send_gossip(int random_id) {
int i = 0;
int count = client_count;
int j = gossip_count;
int recvr = random_id;
if(alive[id]) {
for(i = 0; i<client_count+1; i++) {
if(age[id][i]!=-1){
age[id][i]++;
if(age[id][i] >= death_threshold + 1) age[id][i] = death_threshold;
}
}
age[id][id] = 0;
while(j != 0 && count != 0) {
if(recvr != id && opinion[id][recvr] != -1) {
update_state_from_gossip(id, recvr);
j--;
}
recvr = recvr % client_count + 1;
count--;
}
}
}</declaration>
<location id="id5" x="-807" y="-425">
<name x="-850" y="-434">idle</name>
<label kind="invariant" x="-926" y="-417">g_clk <= delay</label>
</location>
<location id="id6" x="-544" y="-425">
<name x="-527" y="-434">halt</name>
</location>
<init ref="id5"/>
<transition>
<source ref="id5"/>
<target ref="id5"/>
<label kind="select" x="-909" y="-587">random_id : int[1, client_count]</label>
<label kind="guard" x="-918" y="-570">g_clk >= delay and halted == 0</label>
<label kind="assignment" x="-926" y="-553">g_clk = 0, send_gossip(random_id)</label>
<nail x="-705" y="-527"/>
<nail x="-909" y="-527"/>
</transition>
<transition>
<source ref="id5"/>
<target ref="id6"/>
<label kind="guard" x="-790" y="-417">g_clk >= delay and halted == 1</label>
</transition>
</template>
<template>
<name>GossipSetReviser</name>
<declaration>clock gsr_clk;
void clear_req_count() {
int i;
for(i = 0; i<client_count + 1; i++) {
req_count[i] = 0;
}
version++;
}
void send_gossip_set() {
int i = 0;
int j = infection_count;
int k = 0;
if(available == 1) {
for(i = 1; i<client_count + 1; i++) {
if(req_count[i] > 0 && j!=0) {
vid[i] = version;
j--;
for(k = 1; k<client_count+1; k++) {
if(req_count[k] > 0 && opinion[i][k] == -1) {
opinion[i][k] = 0;
age[i][k] = 10;
} else if(req_count[k] == 0){
opinion[i][k] = -1;
age[i][k] = -1;
}
}
}
}
}
clear_req_count();
}</declaration>
<location id="id7" x="-501" y="-187">
<name x="-543" y="-195">idle</name>
<label kind="invariant" x="-688" y="-178">gsr_clk <= revision_time</label>
</location>
<location id="id8" x="-170" y="-187">
<name x="-153" y="-195">halt</name>
</location>
<init ref="id7"/>
<transition>
<source ref="id7"/>
<target ref="id7"/>
<label kind="guard" x="-637" y="-340">gsr_clk >= revision_time and halted == 0</label>
<label kind="assignment" x="-594" y="-323">gsr_clk = 0, send_gossip_set()</label>
<nail x="-433" y="-255"/>
<nail x="-390" y="-297"/>
<nail x="-603" y="-297"/>
</transition>
<transition>
<source ref="id7"/>
<target ref="id8"/>
<label kind="guard" x="-484" y="-170">gsr_clk >= revision_time and halted == 1</label>
</transition>
</template>
<template>
<name>Client</name>
<parameter>const int cid</parameter>
<declaration>clock clk;
const int waiting_delay = 4;
int [0,3] cb = 0; // DCBN State - 0 -> Closed, 1 -> Open, 2 -> Half Open, 3 -> Suspicion
int [0,FT] clientTO = 0; // Timeout counter for each client
int [0,HOST] cbSuccess = 0; // Success counter for Half-Open State
int [-1,1] window[10] = {-1,-1,-1,-1,-1,-1,-1,-1,-1,-1}; // Window of requests with respective status. 0 -> Success, 1 -> Timeout, -1 -> Empty slot
int [0,9] wptr = 0; // Window pointer
// Reset client data structures when client dies
void resetIfDead() {
int i = 0;
cb = 0;
clientTO = 0;
cbSuccess = 0;
for(i = 0; i<window_size; i++) {
window[i] = -1;
}
}
// Pushes request to the server queue
void push() {
buf[tail] = cid;
tail = (client_count + tail - 1) % client_count;
buf_count++;
CPRC--;
}
// Breaks connection from the server and removes the request it had added to the queue
void break_conn() {
int i = 0;
int j = 0;
int found = 0;
int pos;
for (i = 0; i < client_count; i++) {
if (buf[i] == cid) {
buf[i] = 0;
pos = i;
found = 1;
}
}
if(found == 0) return;
if (pos != head) {
i = pos;
j = (client_count + i - 1) % client_count;
while (j != tail) {
buf[i] = buf[j];
i = j;
j = (client_count + j - 1) % client_count;
}
buf[i] = 0;
tail = i;
buf_count--;
}
}
// Utility function to clear the window of requests the DCBN is tracking
void reset_counters() {
int i = 0;
clientTO = 0;
cbSuccess = 0;
for(i = 0; i<window_size; i++) {
window[i] = -1;
}
}
// Register the occurance of timeout into the data structure of a client with ID cid
void register_timeout() {
int i = 0;
if(cid == 0) return;
window[wptr] = 1;
wptr = (wptr + 1) % window_size;
clientTO = 0;
for(i = 0; i<window_size; i++) {
if(window[i] == 1) clientTO++;
}
}
// Register the receipt of successful response into the data structure of a client with ID cid
void register_success() {
int i = 0;
window[wptr] = 0;
wptr = (wptr + 1) % window_size;
clientTO = 0;
for(i = 0; i<window_size; i++) {
if(window[i] == 1) clientTO++;
}
}
// DCBN state machine failure handling logic
void cb_timeout_handler() {
if(cb == 3 && clientTO == FT) {
reset_counters();
cb = 1;
opinion[cid][cid] = 1;
} else if(cb == 0 && clientTO == softFT) {
cb = 3;
cbSuccess = 0;
opinion[cid][cid] = 1;
} else if(cb == 2 && clientTO == HOFT) {
reset_counters();
cb = 1;
opinion[cid][cid] = 1;
}
}
// DCBN state machine success handling logic
void cb_success_handler() {
if(cb == 2) {
cbSuccess++;
if(cbSuccess == HOST) {
reset_counters();
cb = 0;
opinion[cid][cid] = 0;
}
} else if(cb == 3) {
cbSuccess++;
if(cbSuccess == SST) {
reset_counters();
cb = 0;
opinion[cid][cid] = 0;
}
}
}
void check_for_suspicion() {
int i = 0;
int sus_count = 0;
int total_count = 0;
int majority;
if(cb != 3) return;
for(i = 1; i<client_count + 1; i++) {
if(age[cid][i] != -1 && age[cid][i] <= death_threshold){
total_count++;
if(opinion[cid][i] == 1) sus_count++;
}
}
if(total_count % 2 == 0) majority = total_count / 2 + 1;
else majority = (total_count + 1)/2;
if(total_count > 1 && sus_count >= majority) {
cb = 1;
reset_counters();
opinion[cid][cid] = 1;
}
}
void handle_timeout() {
CPRC++;
TC++;
if(alive[cid] == 1) {
register_timeout();
cb_timeout_handler();
check_for_suspicion();
}
break_conn();
}
void handle_response() {
if(alive[cid] == 1) {
register_success();
cb_success_handler();
check_for_suspicion();
}
}
</declaration>
<location id="id9" x="-765" y="-510">
<name x="-807" y="-518">idle</name>
<label kind="invariant" x="-884" y="-518">clk <= 0</label>
</location>
<location id="id10" x="-289" y="-510">
<name x="-272" y="-519">blocked</name>
<label kind="invariant" x="-340" y="-484">clk <= time_out</label>
</location>
<location id="id11" x="-961" y="-366">
<name x="-944" y="-374">halt</name>
</location>
<location id="id12" x="-603" y="-348">
<name x="-586" y="-357">open_circuit</name>
<label kind="invariant" x="-586" y="-340">clk <= OD</label>
</location>
<location id="id13" x="-1028" y="-697">
<name x="-1038" y="-731">wait</name>
<label kind="invariant" x="-1130" y="-748">clk <= waiting_delay</label>
</location>
<init ref="id9"/>
<transition>
<source ref="id13"/>
<target ref="id9"/>
<label kind="guard" x="-1122" y="-603">clk >= waiting_delay</label>
<label kind="assignment" x="-1020" y="-586">clk = 0</label>
<nail x="-969" y="-603"/>
</transition>
<transition>
<source ref="id9"/>
<target ref="id13"/>
<label kind="guard" x="-977" y="-680">(halted == 0 and CPRC == 0 and alive[cid] == 1 and cb != 1) or (halted == 0 and alive[cid] == 0)</label>
<label kind="assignment" x="-943" y="-654">resetIfDead()</label>
</transition>
<transition>
<source ref="id12"/>
<target ref="id9"/>
<label kind="guard" x="-654" y="-467">clk >= OD</label>
<label kind="assignment" x="-654" y="-450">cb = 2, clk = 0</label>
<nail x="-612" y="-391"/>
<nail x="-705" y="-484"/>
</transition>
<transition>
<source ref="id9"/>
<target ref="id12"/>
<label kind="guard" x="-875" y="-416">halted == 0 and alive[cid] == 1 and cb == 1</label>
</transition>
<transition>
<source ref="id10"/>
<target ref="id9"/>
<label kind="guard" x="-603" y="-646">clk >=time_out</label>
<label kind="assignment" x="-629" y="-629">clk = 0, handle_timeout()</label>
<nail x="-365" y="-629"/>
<nail x="-705" y="-629"/>
</transition>
<transition>
<source ref="id10"/>
<target ref="id9"/>
<label kind="guard" x="-663" y="-586">clk < time_out</label>
<label kind="synchronisation" x="-552" y="-586">respond[cid]?</label>
<label kind="assignment" x="-637" y="-569">clk = 0, handle_response()</label>
<nail x="-382" y="-569"/>
<nail x="-680" y="-569"/>
</transition>
<transition>
<source ref="id9"/>
<target ref="id11"/>
<label kind="guard" x="-952" y="-459">halted == 1</label>
</transition>
<transition>
<source ref="id9"/>
<target ref="id10"/>
<label kind="guard" x="-739" y="-527">halted == 0 and alive[cid] == 1 and CPRC > 0 and cb != 1</label>
<label kind="assignment" x="-561" y="-510">push()</label>
</transition>
</template>
<template>
<name>ClientShuffler</name>
<declaration>clock s_clk;
void shuffle(int cid) {
int i = 0;
int k = 0;
int j = inactive_clients;
int client = cid;
for(i = 0; i<client_count+1; i++) {
if(alive[i] == 0) {
for(k = 0; k<client_count + 1; k++) {
opinion[i][k] = -1;
age[i][k] = -1;
}
}
alive[i] = 1;
}
while(j != 0) {
alive[client] = 0;
for(i = 0; i<client_count + 1; i++) {
opinion[client][i] = -1;
age[client][i] = -1;
}
client = ((client) % (client_count)) + 1;
j--;
}
}</declaration>
<location id="id14" x="-680" y="-204">
<name x="-731" y="-229">idle</name>
<label kind="invariant" x="-824" y="-212">s_clk <= s_delay</label>
</location>
<location id="id15" x="-399" y="-204">
<name x="-382" y="-213">halt</name>
</location>
<init ref="id14"/>
<transition>
<source ref="id14"/>
<target ref="id14"/>
<label kind="select" x="-731" y="-357">cid : int[1, client_count]</label>
<label kind="guard" x="-765" y="-340">s_clk >= s_delay and halted == 0</label>
<label kind="assignment" x="-731" y="-315">s_clk = 0, shuffle(cid)</label>
<nail x="-629" y="-247"/>
<nail x="-561" y="-315"/>
<nail x="-748" y="-314"/>
</transition>
<transition>
<source ref="id14"/>
<target ref="id15"/>
<label kind="guard" x="-663" y="-195">s_clk >= s_delay and halted == 1</label>
</transition>
</template>
<system>server = Server();
c1 = Client(1);
c2 = Client(2);
c3 = Client(3);
c4 = Client(4);
c5 = Client(5);
c6 = Client(6);
c7 = Client(7);
c8 = Client(8);
g1 = Gossiper(1);
g2 = Gossiper(2);
g3 = Gossiper(3);
g4 = Gossiper(4);
g5 = Gossiper(5);
g6 = Gossiper(6);
g7 = Gossiper(7);
g8 = Gossiper(8);
cs = ClientShuffler();
gsr = GossipSetReviser();
system c1, c2, c3, c4, c5, c6, c7, c8, server, g1, g2, g3, g4, g5, g6, g7, g8, cs, gsr;
</system>
<queries>
<query>
<formula>simulate [<=10500; 1] {TC}</formula>
<comment>Query to observe a time-bound whithin which TC stops increasing. We use this time-bound in other SMC queries.</comment>
</query>
<query>
<formula>E[<=10500; 500](max: exec)</formula>
<comment>Query to obtain the expected time needed by the server to addressing MRC number of requests.</comment>
</query>
<query>
<formula>E[<=10500; 500](max: TC)</formula>
<comment>Query to obtain expected number of timeouts experienced by the system for addressing MRC number of requests.</comment>
</query>
</queries>
</nta>