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所以我模擬了一個有四個隊列（每個方向）和一個全局交集Q的汽車交叉口。程序運行良好，沒有使用usleep註釋掉）。但是當我使用睡覺時，沒有任何反應。在線程中添加usleep（）後，程序被禁止（無輸出）
我確定它是因爲被推入globalQ的localID不同於在本地（定向）隊列中被推入的localID。 （localID == northQ.front（）） &（localID == globalQ.front（）））「 永遠不會滿足。
原因我在介紹「usleep（getrand（100000，3000000））;」是因爲我想爲賽車的速度添加一些隨機性。我知道這可能有點混亂。但重點是程序運行時沒有睡眠命令。但是當我介紹它時，沒有任何反應......我猜想有些飢餓。
編輯：主要4個功能是相同的東西。只是不同的隊列名稱。
EDIT2：如果我睡了一定的時間，程序就能正常工作。如果那個時間是我指定的某個時間間隔的隨機數，它就不起作用。
代碼：
// Instructions
// Change the CARS and RUN_TIME variable to the desired values.
// Compile in command line using: g++ -pthread Intelligent_Traffic_Light_System.cpp -o run.exe
// Run in command line by using: ./run.exe
#include <iostream>
#include <pthread.h>
#include <queue>
#include <cstdlib> //for rand()
#include <unistd.h> // for usleep()
#include <ctime> //for clock(), clock_t, CLOCKS_PER_SEC
#define CARS 10 // # cars coming from each direction. 40 cars total
#define RUN_TIME 125 // 125 seconds (5 seconds longer than it should take to run)
using namespace std;
int globalID; // global ID for each car arriving at the intersection
// a queue for each direction.
queue<int> northQ;
queue<int> eastQ;
queue<int> southQ;
queue<int> westQ;
queue<int> globalQ;
pthread_t threadID;
// a lock for each queue/direction.
pthread_mutex_t northLock;
pthread_mutex_t eastLock;
pthread_mutex_t southLock;
pthread_mutex_t westLock;
pthread_mutex_t globalQlock;
pthread_mutex_t globalIDLock; // lock for changing the globalid (i.e. car id)
pthread_mutex_t intersectionLock; // lock for one car passing through the intersection
int getrand(int min,int max) //random number generator between min and max
{
return(rand()%(max-min)+min);
}
void init()
{
globalID = 1; //first car will have ID = 1
pthread_mutex_init(&northLock, NULL);
pthread_mutex_init(&eastLock, NULL);
pthread_mutex_init(&southLock, NULL);
pthread_mutex_init(&westLock, NULL);
pthread_mutex_init(&globalIDLock, NULL);
pthread_mutex_init(&intersectionLock, NULL);
pthread_mutex_init(&globalQlock, NULL);
}
// Now will test to create an intersection with only 1 direction. North
void *north(void *null)
{
int localID;
double duration; //for checking how long a car will be waiting at the front of its lane
clock_t start; //variable will be used to calculate wait time
pthread_mutex_lock(&northLock); // locking the queue
pthread_mutex_lock(&globalIDLock); // locking globalIDLock mutex in order to update globalID
localID = globalID++; // update globalID after reserving that ID for a car in north lane
pthread_mutex_unlock(&globalIDLock);
northQ.push(localID); // pushing the local car into northQ.
pthread_mutex_unlock(&northLock);
//usleep(getrand(100000, 3000000)); //lets say it takes somewhere between 1/10th of a second and 3 seconds to get to the intersection.
start = clock(); // Now the car has arrived at intersection. Let's start the timer.
pthread_mutex_lock(&globalQlock);
globalQ.push(localID);//pushing car into global (intersection Q)
//cout << localID <<endl;
pthread_mutex_unlock(&globalQlock);
while(1) //Checking cars properties here
{
if ((localID == northQ.front()) && (localID == globalQ.front())) // Current Car is in the front of the lane... Lets Proceed
{
break;
}
else //Current car is not in front on its lane. Lets wait
{
usleep(10); // sleep for 10 microsecond to allow for other cars to proceed if they must
continue;
}
}
// Car is in the front so let's proceed to allow it to pass through intersection.
pthread_mutex_lock(&intersectionLock); // need to lock the intersection. Function call will block until mutex is available
duration = (std::clock() - start)/(double) CLOCKS_PER_SEC;
northQ.pop();
globalQ.pop();
cout << "Car from NORTH lane with ID: " << localID << " ENTERING the intersection." << endl;
cout << "It has been waiting at the light for: "<< duration<<" seconds."<<endl;
sleep(3);
cout << "Car from NORTH lane with ID: " << localID << " LEAVING the intersection." << endl<<endl;
pthread_mutex_unlock(&intersectionLock); // give other cars a chance to pass
}
void *east(void *null)
{
int localID;
double duration;
clock_t start;
pthread_mutex_lock(&eastLock); // locking the queue
pthread_mutex_lock(&globalIDLock); // locking globalIDLock mutex in order to update globalID
localID = globalID++; // update globalID after reserving that ID for a car in north lane
pthread_mutex_unlock(&globalIDLock);
eastQ.push(localID); // pushing the local car into northQ.
pthread_mutex_unlock(&eastLock);
//usleep(getrand(100000, 3000000)); //lets say it take 1/10th of a second to get to the intersection.
start = clock();
pthread_mutex_lock(&globalQlock);
globalQ.push(localID);//pushing car into global queue (i.e. intersection queue)
pthread_mutex_unlock(&globalQlock);
while(1) //Checking cars properties here
{
if ((localID == eastQ.front()) && (localID == globalQ.front())) // Current Car is in the front of the lane... Lets Proceed
{
break;
}
else //Current car is not in front on its lane. Lets wait
{
usleep(10); // sleep for 10 microsecond to allow for other cars to proceed if they must
continue;
}
}
// Car is in the front so let's proceed to allow it to pass through intersection.
pthread_mutex_lock(&intersectionLock); // need to lock the intersection. Function call will block until mutex is available
duration = (std::clock() - start)/(double) CLOCKS_PER_SEC;
eastQ.pop();
globalQ.pop();
cout << "Car from EAST lane with ID: " << localID << " ENTERING the intersection." << endl;
cout << "It has been waiting at the light for: "<<duration<<" seconds."<<endl;
sleep(3);
cout << "Car from EAST lane with ID: " << localID << " LEAVING the intersection." << endl <<endl;
pthread_mutex_unlock(&intersectionLock); // give other cars a chance to pass
}
void *south(void *null)
{
int localID;
double duration;
clock_t start;
pthread_mutex_lock (&southLock); // locking the queue
pthread_mutex_lock (&globalIDLock); // locking globalIDLock mutex in order to update globalID
localID = globalID++; // update globalID after reserving that ID for a car in north lane
pthread_mutex_unlock (&globalIDLock);
southQ.push(localID); // pushing the local car into northQ.
pthread_mutex_unlock (&southLock);
//usleep(getrand(100000, 3000000)); //lets say it take 1/10th of a second to get to the intersection.
start = clock();
pthread_mutex_lock(&globalQlock);
globalQ.push(localID);//pushing car into global (intersection Q)
pthread_mutex_unlock(&globalQlock);
while(1) //Checking cars properties here
{
if ((localID == southQ.front()) && (localID == globalQ.front())) // Current Car is in the front of the lane... Lets Proceed
{
break;
}
else //Current car is not in front on its lane. Lets wait
{
usleep(10); // sleep for 10 microsecond to allow for other cars to proceed if they must
continue;
}
}
// Car is in the front so let's proceed to allow it to pass through intersection.
pthread_mutex_lock(&intersectionLock); // need to lock the intersection. Function call will block until mutex is available
duration = (std::clock() - start)/(double) CLOCKS_PER_SEC;
southQ.pop();
globalQ.pop();
cout << "Car from SOUTH lane with ID: " << localID << " ENTERING the intersection." << endl;
cout << "It has been waiting at the light for: "<<duration<< " seconds."<<endl;
sleep(3);
cout << "Car from SOUTH lane with ID: " << localID << " LEAVING the intersection." << endl<<endl;
pthread_mutex_unlock(&intersectionLock); // give other cars a chance to pass
}
void *west(void *null)
{
int localID;
double duration;
clock_t start;
pthread_mutex_lock (&westLock); // locking the queue
pthread_mutex_lock (&globalIDLock); // locking globalIDLock mutex in order to update globalID
localID = globalID++; // update globalID after reserving that ID for a car in north lane
pthread_mutex_unlock (&globalIDLock);
westQ.push(localID); // pushing the local car into northQ.
pthread_mutex_unlock (&westLock);
//usleep(getrand(100000, 3000000));
start = clock();
pthread_mutex_lock(&globalQlock);
globalQ.push(localID);//pushing car into global (intersection Q)
pthread_mutex_unlock(&globalQlock);
while(1) //Checking cars properties here
{
if ((localID == westQ.front()) && (localID == globalQ.front())) // Current Car is in the front of the lane... Lets Proceed
{
break;
}
else //Current car is not in front on its lane. Lets wait
{
usleep(10); // sleep for 10 microsecond to allow for other cars to proceed if they must
continue;
}
}
// Car is in the front so let's proceed to allow it to pass through intersection.
pthread_mutex_lock(&intersectionLock); // need to lock the intersection. Function call will block until mutex is available
duration = (std::clock() - start)/(double) CLOCKS_PER_SEC;
westQ.pop();
globalQ.pop();
cout << "Car from WEST lane with ID: " << localID << " ENTERING the intersection." << endl;
cout << "It has been waiting for: "<< duration <<" seconds."<< endl;
sleep(3);
cout << "Car from WEST lane with ID: " << localID << " LEAVING the intersection." << endl<<endl;
pthread_mutex_unlock(&intersectionLock); // give other cars a chance to pass
}
int main()
{
init();
for(int i = 0; i < CARS; i++) //first car will be car with ID 1; Last ID is 40
{
pthread_create (&threadID, NULL, north, NULL);
pthread_create (&threadID, NULL, east, NULL);
pthread_create (&threadID, NULL, south, NULL);
pthread_create (&threadID, NULL, west, NULL);
}
sleep(RUN_TIME); //sleep for sufficient times to allow for all threads to finish running.
cout << "Finished." << endl;
return 0;
}
這是真的** [最小工作示例]（http://stackoverflow.com/help/mcve）**？ –
[useconds參數應小於一百萬。如果useconds的值爲0，則調用不起作用。]（http://pubs.opengroup.org/onlinepubs/009695399/functions/usleep.html） – POTEMKINDX