I am having some issues with my implementation of the producer-consumer problem. It seems to run fine for the most part, but when I implemented a log file for the capture of critical events, I realized that there was some duplication of events. Would this be due to file manipulation not being mutually exclusive or is there something else that would be causing this? I am running the code on a Ubuntu 12.04 VM.
#include <iostream>
#include <pthread.h>
#include <cstdlib>
#include <signal.h>
#include <unistd.h>
#include <time.h>
#include <stdio.h>
#include <sstream>
using namespace std;
string trimspace(string);
char* createString(string);
void* producer();
void* consumer();
void createArray(int);
int produceItem();
void createProducers(int);
void createConsumers(int);
void signalHandler(int);
int full=0;
int front=0;
int rear=0;
int empty;
int BUFFER_SIZE;
int producerCount;
int consumerCount;
int* buffer;
bool running;
FILE* logFile;
timespec pts;
timespec cts;
pthread_t* producers;
pthread_t* consumers;
pthread_mutex_t counter_mutex= PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t condp_mutex= PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t condc_mutex= PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condVarProd;
pthread_cond_t condVarCons;
int main()
{
running=true;
pthread_cond_init(&condVarCons,NULL);
pthread_cond_init(&condVarProd,NULL);
srand ( time(NULL) );
signal(SIGINT, signalHandler);
full=0;
BUFFER_SIZE=0;
string data;
cout<<"How many producers would you like to create? ";
getline(cin,data);
data=trimspace(data);
char* data2=createString(data);
producerCount=atoi(data2);
free (data2);
while (producerCount<=0){
cout<<"Please enter a valid number of producers to create! ";
getline(cin,data);
data=trimspace(data);
data2=createString(data);
producerCount=atoi(data2);
free (data2);
}
cout<<"How many consumers would you like to create? ";
getline(cin,data);
data=trimspace(data);
data2=createString(data);
consumerCount=atoi(data2);
free(data2);
while (consumerCount<=0){
cout<<"Please enter a valid number of consumers to create! ";
getline(cin,data);
data=trimspace(data);
data2=createString(data);
consumerCount=atoi(data2);
free (data2);
}cout<<"How large of a rotating buffer would you like to create? ";
getline(cin,data);
data=trimspace(data);
data2=createString(data);
BUFFER_SIZE=atoi(data2);
free(data2);
while (BUFFER_SIZE<=0){
cout<<"Please enter a valid buffer size to create! ";
getline(cin,data);
data=trimspace(data);
data2=createString(data);
BUFFER_SIZE=atoi(data2);
free (data2);
}
cout<<"What would you like to name your logfile? ";
getline (cin,data);
data=trimspace(data);
data2=createString(data);
logFile=fopen(data2,"a");
free(data2);
empty=BUFFER_SIZE;
createArray(BUFFER_SIZE);
int i;
createProducers(producerCount);
createConsumers(consumerCount);
for (i=0; i<producerCount;i++){
pthread_create(&producers[i], NULL, (void * (*)(void *))&producer, NULL);
}
for (i=0; i<consumerCount;i++){
pthread_create(&consumers[i], NULL, (void * (*)(void *))&consumer, NULL);
}
while(true);
return 0;
}
void createArray(int size){
if (!buffer){
buffer=(int*)malloc(size*sizeof(int));
}
}
void createProducers(int size){
if (!producers){
producers=(pthread_t*)malloc(size*sizeof(pthread_t*));
}
}
void createConsumers(int size){
if (!consumers){
consumers=(pthread_t*)malloc(size*sizeof(pthread_t*));
}
}
void * producer(){
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS,NULL);
stringstream loginfo;
while (running){
pthread_mutex_lock(&condp_mutex); //sets mutual exclusion for the producer
clock_gettime(CLOCK_REALTIME,&pts);
loginfo<<pts.tv_nsec<<": Producer "<<pthread_self()<< "entered critical section.\n";
char* logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
int item = produceItem();
//down(empty); //we will have one less empty slot when this is done
while (empty==0){
clock_gettime(CLOCK_REALTIME,&pts);
loginfo<<pts.tv_nsec<<": Producer "<<pthread_self()<<" encountered full buffer.\n";
logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
pthread_cond_wait(&condVarProd,&condp_mutex);
}
//pthread_mutex_lock(&condp_mutex); //sets mutual exclusion for the producer
empty--;
buffer[rear]=item;
int rear2=rear;
rear=((rear+1)%BUFFER_SIZE);
clock_gettime(CLOCK_REALTIME,&pts);
loginfo<<pts.tv_nsec<<": Item created by "<<pthread_self()<<" into slot "<<rear2<<". Value: "<<item<<". \n";
logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
//write to log file
full++;
pthread_cond_signal(&condVarCons);
clock_gettime(CLOCK_REALTIME,&pts);
loginfo<<pts.tv_nsec<<": Producer "<<pthread_self()<< "left critical section.\n";
logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
pthread_mutex_unlock(&condp_mutex);
usleep(rand()%5000000);
//releases mutual exclusion for the producer
//up(full); //now that this is complete, we have one more full slot
//struct timespec req={(rand()%5000+1)*1000000},rem={0};
//nanosleep(&req, &rem); //sleeps for 1 millisecond - 5 seconds
}
}
void* consumer(){
pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS,NULL);
stringstream loginfo;
while (running){
//down (&full);
pthread_mutex_lock(&condc_mutex);
clock_gettime(CLOCK_REALTIME,&cts);
loginfo<<cts.tv_nsec<<": Consumer "<<pthread_self()<< "entered critical section.\n";
char* logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
while (full==0){
clock_gettime(CLOCK_REALTIME,&cts);
loginfo<<cts.tv_nsec<<": Consumer "<<pthread_self()<<" encountered empty buffer.\n";
logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
pthread_cond_wait(&condVarCons,&condc_mutex);
}
full--;
//pthread_mutex_lock(&condc_mutex);
int item=buffer[front];
int front2=front;
front=((front+1)%BUFFER_SIZE);
clock_gettime(CLOCK_REALTIME,&cts);
loginfo<<cts.tv_nsec<<": Item removed by "<<pthread_self()<<" from slot "<<front2<<". Value: "<<item<<". \n";
logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
//write to log file
empty++;
pthread_cond_signal(&condVarProd);
clock_gettime(CLOCK_REALTIME,&cts);
loginfo<<cts.tv_nsec<<": Consumer "<<pthread_self()<< "left critical section.\n";
logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
pthread_mutex_unlock(&condc_mutex);
//up(&empty);
usleep(rand()%5000000);
//struct timespec req={(rand()%5000+1)*1000000},rem={0};
//nanosleep(&req, &rem); //sleeps for 1 millisecond - 5 seconds
}
}
string trimspace(string str){ //trims leading and trailing space off string and returns new string
size_t startpos=str.find_first_not_of(" ");
size_t endpos=str.find_last_not_of(" ");
return str.substr(startpos, endpos-startpos+1);
}
char* createString(string str){ //converts a string to a c string using malloc
char* c=(char*)malloc(str.length()+1);
int i;
for (i=0;i<str.length();i++){
c[i]=str[i];
}
c[i]='\0';
return c;
}
int produceItem(){ //creates and returns an integer (item)
int item= rand()%1000000+1; //random int is between 1 and 1,000,000
return item;
}
void signalHandler( int signum )
{
if (signum==SIGINT){
running=false;
cout<<"\nEnding application... \n";
fclose(logFile);
//int i;
for (i=0;i<producerCount;i++){
pthread_cancel(producers[i]);
//pthread_join(producers[i],NULL);
}for (i=0;i<consumerCount;i++){
pthread_cancel(consumers[i]);
//pthread_join(consumers[i],NULL);
//}
exit(0);
}
}
This produced the following within one logfile on one trial. As you can see there are duplicate events appearing, but it appears to be working fine as far as the order in which items are created and removed (comparing timestamps with thread id, buffer slot, and value stored/recovered):
390783278: Producer 139708484286208entered critical section.
390783278: Producer 139708484286208entered critical section.
391751560: Item created by 139708484286208 into slot 0. Value: 994902.
390783278: Producer 139708484286208entered critical section.
391751560: Item created by 139708484286208 into slot 0. Value: 994902.
391758681: Producer 139708484286208left critical section.
391766506: Producer 139708475893504entered critical section.
391766506: Producer 139708475893504entered critical section.
391788442: Item created by 139708475893504 into slot 1. Value: 452289.
391766506: Producer 139708475893504entered critical section.
391788442: Item created by 139708475893504 into slot 1. Value: 452289.
391790768: Producer 139708475893504left critical section.
391799767: Producer 139708492678912entered critical section.
391799767: Producer 139708492678912entered critical section.
391807766: Item created by 139708492678912 into slot 2. Value: 775797.
391799767: Producer 139708492678912entered critical section.
391807766: Item created by 139708492678912 into slot 2. Value: 775797.
391809898: Producer 139708492678912left critical section.
391815624: Producer 139708425537280entered critical section.
391815624: Producer 139708425537280entered critical section.
391824889: Item created by 139708425537280 into slot 3. Value: 40803.
391815624: Producer 139708425537280entered critical section.
391824889: Item created by 139708425537280 into slot 3. Value: 40803.
391827189: Producer 139708425537280left critical section.
391832787: Producer 139708442322688entered critical section.
391832787: Producer 139708442322688entered critical section.
391839933: Item created by 139708442322688 into slot 4. Value: 859933.
391832787: Producer 139708442322688entered critical section.
391839933: Item created by 139708442322688 into slot 4. Value: 859933.
391842089: Producer 139708442322688left critical section.
391847512: Producer 139708433929984entered critical section.
391847512: Producer 139708433929984entered critical section.
391857473: Item created by 139708433929984 into slot 5. Value: 862962.
391847512: Producer 139708433929984entered critical section.
391857473: Item created by 139708433929984 into slot 5. Value: 862962.
391859600: Producer 139708433929984left critical section.
391865631: Producer 139708417144576entered critical section.
391865631: Producer 139708417144576entered critical section.
391872901: Item created by 139708417144576 into slot 6. Value: 464855.
391865631: Producer 139708417144576entered critical section.
391872901: Item created by 139708417144576 into slot 6. Value: 464855.
391874995: Producer 139708417144576left critical section.
391880352: Producer 139708450715392entered critical section.
391880352: Producer 139708450715392entered critical section.
391888990: Item created by 139708450715392 into slot 7. Value: 50160.
391880352: Producer 139708450715392entered critical section.
391888990: Item created by 139708450715392 into slot 7. Value: 50160.
391891063: Producer 139708450715392left critical section.
391896778: Producer 139708459108096entered critical section.
391896778: Producer 139708459108096entered critical section.
391903950: Item created by 139708459108096 into slot 8. Value: 498178.
391896778: Producer 139708459108096entered critical section.
391903950: Item created by 139708459108096 into slot 8. Value: 498178.
391906072: Producer 139708459108096left critical section.
391911508: Producer 139708467500800entered critical section.
391911508: Producer 139708467500800entered critical section.
391920487: Item created by 139708467500800 into slot 9. Value: 917334.
391911508: Producer 139708467500800entered critical section.
391920487: Item created by 139708467500800 into slot 9. Value: 917334.
391922544: Producer 139708467500800left critical section.
391637865: Consumer 139708350002944entered critical section.
391637865: Consumer 139708350002944entered critical section.
391930791: Item removed by 139708350002944 from slot 0. Value: 994902.
391637865: Consumer 139708350002944entered critical section.
391930791: Item removed by 139708350002944 from slot 0. Value: 994902.
391933158: Consumer 139708350002944left critical section.
391967700: Consumer 139708358395648entered critical section.
391967700: Consumer 139708358395648entered critical section.
391976740: Item removed by 139708358395648 from slot 1. Value: 452289.
391967700: Consumer 139708358395648entered critical section.
391976740: Item removed by 139708358395648 from slot 1. Value: 452289.
391978960: Consumer 139708358395648left critical section.
391984926: Consumer 139708341610240entered critical section.
391984926: Consumer 139708341610240entered critical section.
391994663: Item removed by 139708341610240 from slot 2. Value: 775797.
391984926: Consumer 139708341610240entered critical section.
391994663: Item removed by 139708341610240 from slot 2. Value: 775797.
391996774: Consumer 139708341610240left critical section.
392002719: Consumer 139708366788352entered critical section.
392002719: Consumer 139708366788352entered critical section.
392009664: Item removed by 139708366788352 from slot 3. Value: 40803.
392002719: Consumer 139708366788352entered critical section.
392009664: Item removed by 139708366788352 from slot 3. Value: 40803.
392011765: Consumer 139708366788352left critical section.
392017278: Consumer 139708375181056entered critical section.
392017278: Consumer 139708375181056entered critical section.
392026094: Item removed by 139708375181056 from slot 4. Value: 859933.
392017278: Consumer 139708375181056entered critical section.
392026094: Item removed by 139708375181056 from slot 4. Value: 859933.
392028216: Consumer 139708375181056left critical section.
392034061: Consumer 139708383573760entered critical section.
392034061: Consumer 139708383573760entered critical section.
392036228: Item removed by 139708383573760 from slot 5. Value: 862962.
392034061: Consumer 139708383573760entered critical section.
392036228: Item removed by 139708383573760 from slot 5. Value: 862962.
392041046: Consumer 139708383573760left critical section.
392046521: Consumer 139708408751872entered critical section.
392046521: Consumer 139708408751872entered critical section.
392048239: Item removed by 139708408751872 from slot 6. Value: 464855.
392046521: Consumer 139708408751872entered critical section.
392048239: Item removed by 139708408751872 from slot 6. Value: 464855.
392050158: Consumer 139708408751872left critical section.
392054579: Consumer 139708400359168entered critical section.
392054579: Consumer 139708400359168entered critical section.
392056109: Item removed by 139708400359168 from slot 7. Value: 50160.
392054579: Consumer 139708400359168entered critical section.
392056109: Item removed by 139708400359168 from slot 7. Value: 50160.
392058047: Consumer 139708400359168left critical section.
392062556: Consumer 139708391966464entered critical section.
392062556: Consumer 139708391966464entered critical section.
392064062: Item removed by 139708391966464 from slot 8. Value: 498178.
392062556: Consumer 139708391966464entered critical section.
392064062: Item removed by 139708391966464 from slot 8. Value: 498178.
392065952: Consumer 139708391966464left critical section.
392070444: Consumer 139708333217536entered critical section.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392073850: Consumer 139708333217536left critical section.
392017278: Consumer 139708375181056entered critical section.
392026094: Item removed by 139708375181056 from slot 4. Value: 859933.
392028216: Consumer 139708375181056left critical section.
537760776: Consumer 139708375181056entered critical section.
392017278: Consumer 139708375181056entered critical section.
392026094: Item removed by 139708375181056 from slot 4. Value: 859933.
392028216: Consumer 139708375181056left critical section.
537760776: Consumer 139708375181056entered critical section.
537779758: Consumer 139708375181056 encountered empty buffer.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392073850: Consumer 139708333217536left critical section.
818759131: Consumer 139708333217536entered critical section.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392073850: Consumer 139708333217536left critical section.
818759131: Consumer 139708333217536entered critical section.
818777830: Consumer 139708333217536 encountered empty buffer.
391832787: Producer 139708442322688entered critical section.
391839933: Item created by 139708442322688 into slot 4. Value: 859933.
391842089: Producer 139708442322688left critical section.
104776263: Producer 139708442322688entered critical section.
391832787: Producer 139708442322688entered critical section.
391839933: Item created by 139708442322688 into slot 4. Value: 859933.
391842089: Producer 139708442322688left critical section.
104776263: Producer 139708442322688entered critical section.
104794865: Item created by 139708442322688 into slot 10. Value: 729187.
391832787: Producer 139708442322688entered critical section.
391839933: Item created by 139708442322688 into slot 4. Value: 859933.
391842089: Producer 139708442322688left critical section.
104776263: Producer 139708442322688entered critical section.
104794865: Item created by 139708442322688 into slot 10. Value: 729187.
104804537: Producer 139708442322688left critical section.
392017278: Consumer 139708375181056entered critical section.
392026094: Item removed by 139708375181056 from slot 4. Value: 859933.
392028216: Consumer 139708375181056left critical section.
537760776: Consumer 139708375181056entered critical section.
537779758: Consumer 139708375181056 encountered empty buffer.
104823321: Item removed by 139708375181056 from slot 10. Value: 729187.
392017278: Consumer 139708375181056entered critical section.
392026094: Item removed by 139708375181056 from slot 4. Value: 859933.
392028216: Consumer 139708375181056left critical section.
537760776: Consumer 139708375181056entered critical section.
537779758: Consumer 139708375181056 encountered empty buffer.
104823321: Item removed by 139708375181056 from slot 10. Value: 729187.
104838395: Consumer 139708375181056left critical section.
392054579: Consumer 139708400359168entered critical section.
392056109: Item removed by 139708400359168 from slot 7. Value: 50160.
392058047: Consumer 139708400359168left critical section.
305774914: Consumer 139708400359168entered critical section.
392054579: Consumer 139708400359168entered critical section.
392056109: Item removed by 139708400359168 from slot 7. Value: 50160.
392058047: Consumer 139708400359168left critical section.
305774914: Consumer 139708400359168entered critical section.
305793885: Consumer 139708400359168 encountered empty buffer.
392002719: Consumer 139708366788352entered critical section.
392009664: Item removed by 139708366788352 from slot 3. Value: 40803.
392011765: Consumer 139708366788352left critical section.
380742045: Consumer 139708366788352entered critical section.
392002719: Consumer 139708366788352entered critical section.
392009664: Item removed by 139708366788352 from slot 3. Value: 40803.
392011765: Consumer 139708366788352left critical section.
380742045: Consumer 139708366788352entered critical section.
380755715: Consumer 139708366788352 encountered empty buffer.
391865631: Producer 139708417144576entered critical section.
391872901: Item created by 139708417144576 into slot 6. Value: 464855.
391874995: Producer 139708417144576left critical section.
530764064: Producer 139708417144576entered critical section.
391865631: Producer 139708417144576entered critical section.
391872901: Item created by 139708417144576 into slot 6. Value: 464855.
391874995: Producer 139708417144576left critical section.
530764064: Producer 139708417144576entered critical section.
530783146: Item created by 139708417144576 into slot 11. Value: 697827.
391865631: Producer 139708417144576entered critical section.
391872901: Item created by 139708417144576 into slot 6. Value: 464855.
391874995: Producer 139708417144576left critical section.
530764064: Producer 139708417144576entered critical section.
530783146: Item created by 139708417144576 into slot 11. Value: 697827.
530838023: Producer 139708417144576left critical section.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392073850: Consumer 139708333217536left critical section.
818759131: Consumer 139708333217536entered critical section.
818777830: Consumer 139708333217536 encountered empty buffer.
530848657: Item removed by 139708333217536 from slot 11. Value: 697827.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392073850: Consumer 139708333217536left critical section.
818759131: Consumer 139708333217536entered critical section.
818777830: Consumer 139708333217536 encountered empty buffer.
530848657: Item removed by 139708333217536 from slot 11. Value: 697827.
530861640: Consumer 139708333217536left critical section.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392073850: Consumer 139708333217536left critical section.
818759131: Consumer 139708333217536entered critical section.
818777830: Consumer 139708333217536 encountered empty buffer.
530848657: Item removed by 139708333217536 from slot 11. Value: 697827.
530861640: Consumer 139708333217536left critical section.
931760566: Consumer 139708333217536entered critical section.
392070444: Consumer 139708333217536entered critical section.
392071917: Item removed by 139708333217536 from slot 9. Value: 917334.
392073850: Consumer 139708333217536left critical section.
818759131: Consumer 139708333217536entered critical section.
818777830: Consumer 139708333217536 encountered empty buffer.
530848657: Item removed by 139708333217536 from slot 11. Value: 697827.
530861640: Consumer 139708333217536left critical section.
931760566: Consumer 139708333217536entered critical section.
931779060: Consumer 139708333217536 encountered empty buffer.
391766506: Producer 139708475893504entered critical section.
391788442: Item created by 139708475893504 into slot 1. Value: 452289.
391790768: Producer 139708475893504left critical section.
965818384: Producer 139708475893504entered critical section.
391766506: Producer 139708475893504entered critical section.
391788442: Item created by 139708475893504 into slot 1. Value: 452289.
391790768: Producer 139708475893504left critical section.
965818384: Producer 139708475893504entered critical section.
965837852: Item created by 139708475893504 into slot 12. Value: 690947.
391766506: Producer 139708475893504entered critical section.
391788442: Item created by 139708475893504 into slot 1. Value: 452289.
391790768: Producer 139708475893504left critical section.
Essentially, the issue appears whenever I write to the file. For instance, the code generating the first couple lines of the log file would be as follows:
pthread_mutex_lock(&condp_mutex); //sets mutual exclusion for the producer
clock_gettime(CLOCK_REALTIME,&pts);
loginfo<<pts.tv_nsec<<": Producer "<<pthread_self()<< "entered critical section.\n";
char* logstring= createString(loginfo.str());
fprintf(logFile, "%s", logstring);
free(logstring);
In this case, loginfo is a stream that is later converted to a string which is then placed into the log file. In theory, this code should only execute once per entry into the critical section (designated by the locking of the mutex), but it prints into the log file multiple times.
https://stackoverflow.com/questions/19602842
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