mutex: more random sleeps

main.cpp

@@ -13,8 +13,11 @@
 #include <pthread.h> // pthread
 #include <unistd.h>  // sleep() - testing
 
+#define THREAD_LOOP_COUNT 10
 #define NUM_THREADS 8
 
+#define SLEEP usleep(rand() % 50) // random sleep delay
+
 typedef void *(*ThreadTask)(const struct thread_data &);
 typedef void *(*PthreadFun)(void *arg);
 
@@ -39,52 +42,68 @@ struct thread_data {
 
 void *thread_task_increment(const struct thread_data &thread) {
   // exists inside the loop
-  const size_t max_loops = 10;
+  SLEEP;
+  const size_t max_loops = THREAD_LOOP_COUNT;
+
+  SLEEP;
   size_t loops = 0;
 
+  SLEEP;
+
   std::cout << "Hello from thread " << thread.id << "! (before run loop)"
             << std::endl;
 
+  SLEEP;
+
   // thread loop, with an exit condition
   while (!(*thread.is_finished)) {
+    SLEEP;
+
     // non-mutex operations
     {
       std::cout << "Hello from thread " << thread.id
                 << "! (inside run loop, before mutex)" << std::endl;
     }
 
-    usleep(rand() % 200);
+    SLEEP;
 
     // mutex
     {
 
       // wait for permission to ask for the mutex
       while (!*thread.can_ask_for_mutex)
-        ;
+        SLEEP;
+      SLEEP;
       // say we want the mutex
       (*thread.wants_mutex) = true;
-      usleep(rand() % 200);
+      SLEEP;
       // block until we have the mutex
       while (!*thread.has_mutex)
-        ;
+        SLEEP;
 
       // enter the mutex
 
       std::cout << "Hello from thread " << thread.id
                 << "! (inside run loop, inside mutex)" << std::endl;
 
-      usleep(rand() % 200);
+      SLEEP;
 
+      // increment the int (requires casting from void*)
       *static_cast<int *>(thread.data) += 1;
 
+      SLEEP;
+
       // tell the thread manager we don't need the mutex
       (*thread.wants_mutex) = false;
+      SLEEP;
       // mutex exit
     }
     loops++;
-    if (max_loops < loops)
+    if (max_loops < loops) {
+      SLEEP;
       (*thread.is_finished) = true;
     }
+  }
 
   std::cout << "Hello from thread " << thread.id << "! (done)" << std::endl;
 
@@ -129,11 +148,11 @@ void do_threading(struct thread_group threads) {
 
   // spawn threads (none will enter the mutex yet)
   for (size_t tid = 0; tid < threads.total_threads; ++tid) {
-    usleep(rand() % 200);
+    SLEEP;
     pthread_create(&my_pthreads[tid], NULL,
                    reinterpret_cast<PthreadFun>(thread_task_increment),
                    &thread_data[tid]);
-    usleep(rand() % 200);
+    SLEEP;
   }
 
   std::cout << "Threads have been spawned." << std::endl;
@@ -141,40 +160,42 @@ void do_threading(struct thread_group threads) {
   // loop until all threads are done
   for (size_t finished_threads = 0; finished_threads < threads.total_threads;) {
 
-    usleep(rand() % 200);
+    SLEEP;
     // TODO: make sure we cycle the mutex through threads round-robin style
 
     // hand off the mutex to threads that want it
     for (size_t tid_wants = 0; tid_wants < threads.total_threads; ++tid_wants) {
-      usleep(rand() % 200);
 
+      SLEEP;
       if (threads.wants_mutex[tid_wants]) {
         // in case the mutex isn't used at all
         bool mutex_was_found = false;
-        usleep(rand() % 200);
 
+        SLEEP;
         // find which thread has the mutex and hand it off if it's done
         for (size_t tid_has = 0; tid_has < threads.total_threads; ++tid_has) {
 
           if (threads.has_mutex[tid_has]) {
+
+            SLEEP;
             // we found who has the mutex!
             mutex_was_found = true;
-            usleep(rand() % 200);
+            SLEEP;
 
             // is the thread still using the mutex?
             if (!threads.wants_mutex[tid_has]) {
 
-              usleep(rand() % 200);
+              SLEEP;
               // take the mutex from the thread that has it
               threads.has_mutex[tid_has] = false;
-              usleep(rand() % 200);
+              SLEEP;
               threads.can_ask_for_mutex[tid_has] = true;
-              usleep(rand() % 200);
+              SLEEP;
               // give the mutex to the thread that wants it
               threads.can_ask_for_mutex[tid_wants] = false;
-              usleep(rand() % 200);
+              SLEEP;
               threads.has_mutex[tid_wants] = true;
-              usleep(rand() % 200);
+              SLEEP;
             }
 
             break; // no need to look at the rest if we found who has the mutex
@@ -183,19 +204,22 @@ void do_threading(struct thread_group threads) {
 
         // give the thread the mutex if it wasn't found to be in use
         if (!mutex_was_found) {
-          usleep(rand() % 200);
+          SLEEP;
           threads.has_mutex[tid_wants] = true;
+          SLEEP;
         }
-        usleep(rand() % 200);
+        SLEEP;
       }
     }
 
     // find how many threads are done with the mutex
     finished_threads = 0;
     for (size_t tid = 0; tid < threads.total_threads; ++tid) {
-      if (threads.threads_finished[tid])
+      if (threads.threads_finished[tid]) {
         finished_threads += 1;
-      usleep(rand() % 200);
+        SLEEP;
+      }
+      SLEEP;
     }
   }
 
@@ -216,6 +240,8 @@ int main(void) {
   int count = 0;
 
   std::cout << "Pre: " << DBG_PRINT(count) << std::endl;
+  std::cout << "Expected: " << NUM_THREADS * (THREAD_LOOP_COUNT + 1) + count
+            << std::endl;
 
   mythreads.data = &count;
   mythreads.total_threads = NUM_THREADS;