stuff

Examples/concurrency/con4.c

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+/*
+ * con4.c - Concurrency using flag array - version 3
+ *          Sets the critical section flag before the wait
+ *          Allows threads to specify desire for critical secgion
+ *          Adds deadlock detection and relase of the flag if both
+ *          threads have their flag set
+ *          Prone to livelock since threads might be constantly releasing their flag
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <pthread.h>
+
+// shared global
+static int counter1 = 0;
+static int counter2 = 0;
+
+// start flag
+volatile int start = 0;
+
+// flag array
+volatile int flag[2] = {0,0};
+
+void* thread_routine(void* args)
+{
+    int me = *((int *) args);
+
+    int you = me ? 0 : 1;
+
+    printf("Worker thread: %d ready, you are %d\n",me,you);
+
+    // wait for start from master thread
+    while(!start);
+
+    for (int j = 0; j < 1000000; j++)
+    {
+        flag[me] = 1;
+        while(flag[you])
+        {
+            // just in case there is deadlock
+            flag[me] = 0;
+            usleep(1); // enought time to allow other thread to run
+            flag[me] = 1;
+        }
+        // this is the critical section
+        counter1++;
+        counter2++;
+        // leaving critical section
+        flag[me] = 0;
+    }
+
+    printf("Worker thread: %d done\n",me);
+
+    return NULL;
+}
+
+
+int main()
+{
+    int val1 = 0;
+    int val2 = 1;
+
+    pthread_t thr1;
+    pthread_t thr2;
+    if(pthread_create(&thr1, NULL, thread_routine, (void*)&val1) == -1) {
+        printf("COULD NOT CREATE A THREAD\n");
+        exit(EXIT_FAILURE);
+    }
+    if(pthread_create(&thr2, NULL, thread_routine, (void*)&val2) == -1) {
+        printf("COULD NOT CREATE A THREAD\n");
+        exit(EXIT_FAILURE);
+    }
+
+    start = 1;
+
+    pthread_join(thr1,NULL);
+    pthread_join(thr2,NULL);
+
+    printf("counter1: %d\n",counter1);
+    printf("counter2: %d\n",counter2);
+    return EXIT_SUCCESS;
+}