Thread: threads

  1. #1

    Lightbulb threads

    I'm came across this code in a unix book I took out from the library. I know some c++ but I don't know a thing about Unix. I'm curious about it. I tried running this with my MS C++ 6.0, but it gave me an error. Can someone tell me how to compile it and run it. I want to know what this does.


    #include <thread.h>
    #include <synch.h>
    #include <list.h>
    #include <iterator.h>
    #include <iostream.h>

    //creates the structure where the results are placed in the linked list
    struct item
    int value;
    thread_t thrid;
    item(int v = 0, thread_t tid = 0) : value(v), thrid(tid){}

    //Linked Lists: task list and results list
    list<int> tasks;
    list<item> results;
    list<item>::iterator indexItem; //Item list iterator
    list<int>::iterator indexInt; //Integer list iterator

    //Global Variables
    int numberOfTasks; //# of tasks
    int bufferSize; //Size of buffer

    //Two semaphores: tasks and results
    sema_t sTasks;
    sema_t sResults;

    //Flag that signals readers that writer has finished
    bool done = false;

    //Prototypes for the writer(producer) and reader(consumer) functions
    void *reader(void* rn);
    void *writer(void* wri);

    int main (void)
    // Initializes semaphores for 2 lists and cout statements
    if(sema_init(&sTasks, 1, USYNC_THREAD, 0) != 0)
    cout << "ERROR, Task List Semaphore NOT Initialized\n";
    if(sema_init(&sResults, 1, USYNC_THREAD, 0) != 0)
    cout << "ERROR, Result List Semaphore NOT Initialized\n";

    //Get buffer size and number of tasks
    cout << "Enter the total number tasks: ";
    cin >>NumberTasks;
    cout << "\nEnter the buffer size: ";
    cin >> bufferSize;

    //Creates and starts the threads
    thread_t reader1, reader2, writer1;
    if(thr_create(NULL, 0, writer, NULL, THR_BOUND, &writer1)!= 0)
    cout << "Error creating writer1 thread!";
    if(thr_create(NULL, 0, reader, NULL, THR_BOUND, &reader1) != 0)
    cout << "Error creating reader1 thread!";
    if(thr_create(NULL, 0, reader, NULL, THR_BOUND, &reader2) != 0)
    cout << "Error creating reader2 thread!";


    thr_join(writer1, NULL, NULL);
    thr_join(reader1, NULL, NULL);
    thr_join(reader2, NULL, NULL);

    cout << "\n\nTasks to be done: " <<NumberTasks << "\n";
    cout << "Results list size: "<< results.size() << "\n";

    //Initializing both reader counters:
    int r1Count = 0;
    int r2Count = 0;
    struct item mrItem;
    int total = 0;

    //Assigning the results list iterator to the beginning of the linked list
    indexItem = results.begin();
    thread_t temp = indexItem->thrid;

    for(; indexItem != results.end();indexItem++)
    mrItem = *indexItem;
    if(mrItem.thrid ==reader1) r1Count++;
    if(mrItem.thrid == reader2) r2Count++;
    total +=mrItem.value;

    //Printing the results
    cout << "Tasks done by thread " << reader1 << ": "<< r1Count<<"\n";
    cout << "Tasks done by thread " << reader2 << ": "<< r2Count<<"\n";
    cout << "Total done by both threads: " << r1Count + r2Count<<"\n";
    cout << "\nCompleted Task checksum: " << total << "\n";
    cout << "Expected checksum: " << (NumberTasks * (NumberTasks +1)/2) << "\n";

    void *reader(void *rn)
    //I'm not assigning the passed variable to anything since
    //the *rn variable contains nothing anyways

    int i = 0;
    while(!done ||(tasks.size() > 0))
    bool isIf = false;

    if(tasks.size() > 0) // If the tasks list is not empty, this pops an element off it
    isIf = true;
    indexInt = tasks.end();
    i = *indexInt;


    if(isIf) //This makes an output item and pushes it on the results list
    struct item result;
    result.value = i;
    result.thrid = thr_self();


    sema_post(&sTasks); //Terminate
    return NULL;

    void *writer(void *wri)
    for(int i = 1; i <= NumberTasks; i++)
    { //
    sema_wait(&sTasks); // Wait if the buffer is full

    while(tasks.size()>= N)
    sema_post(&sTasks); //Give the readers a chance to pop some tasks off

    //push i on Tasks


    //If this was last loop, set done flag to true
    if(i == NumberTasks)
    done = true;



    done = true; //Terminate
    return NULL;

  2. #2
    I do some stuff on unix, but I have never heard of <thread.h>. It looks like it uses some other stuff besides unix threads. Otherwise it would just include <pthread.h>. In other words, even if you did compile it on a unix platform (ie linux with gcc or g++), you probably still would run into errors.

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