mutex: make light and heavy sleep

main.cpp

@@ -3,17 +3,24 @@
  * @author Blake North <blake.north@digipen.edu>
  */
 
-#include <cstddef>  // size_t
-#include <cstring>  // memset
-#include <iostream> // cout
+#include <cstddef> // size_t
+#include <cstring> // memset
+#include <ctime>
+#include <iostream> // cerr
 #include <vector>   // vector
 
 // used for threads
 #include <pthread.h> // pthread
 #include <unistd.h>  // sleep() - testing
 
+#define THREAD_LOOP_COUNT 10
 #define NUM_THREADS 8
 
+// different lengths of sleep, so the test can run in a reasonable time
+#define RANDSLEEP(c) usleep(rand() % c) // random sleep delay
+#define SLEEP_LIGHT /* RANDSLEEP(10) */       // short sleep, for blocking code
+#define SLEEP_HEAVY RANDSLEEP(100)      // long sleep, for non-blocking code
+
 typedef void *(*ThreadTask)(const struct thread_data &);
 typedef void *(*PthreadFun)(void *arg);
 
@@ -38,49 +45,70 @@ struct thread_data {
 
 void *thread_task_increment(const struct thread_data &thread) {
   // exists inside the loop
-  const size_t max_loops = 10;
+  SLEEP_HEAVY;
+  const size_t max_loops = THREAD_LOOP_COUNT;
+
+  SLEEP_HEAVY;
   size_t loops = 0;
 
-  std::cout << "Hello from thread " << thread.id << "! (before run loop)"
+  SLEEP_HEAVY;
+
+  std::cerr << "Hello from thread " << thread.id << "! (before run loop)"
             << std::endl;
 
+  SLEEP_HEAVY;
+
   // thread loop, with an exit condition
   while (!(*thread.is_finished)) {
+    SLEEP_HEAVY;
+
     // non-mutex operations
     {
-      std::cout << "Hello from thread " << thread.id
+      std::cerr << "Hello from thread " << thread.id
                 << "! (inside run loop, before mutex)" << std::endl;
     }
 
+    SLEEP_HEAVY;
+
     // mutex
     {
 
       // wait for permission to ask for the mutex
       while (!*thread.can_ask_for_mutex)
-        ;
+        SLEEP_LIGHT;
+      SLEEP_HEAVY;
       // say we want the mutex
       (*thread.wants_mutex) = true;
+      SLEEP_HEAVY;
       // block until we have the mutex
       while (!*thread.has_mutex)
-        ;
+        SLEEP_LIGHT;
 
       // enter the mutex
 
-      std::cout << "Hello from thread " << thread.id
+      std::cerr << "Hello from thread " << thread.id
                 << "! (inside run loop, inside mutex)" << std::endl;
 
+      SLEEP_LIGHT;
+
+      // increment the int (requires casting from void*)
       *static_cast<int *>(thread.data) += 1;
 
+      SLEEP_LIGHT;
+
       // tell the thread manager we don't need the mutex
       (*thread.wants_mutex) = false;
+      SLEEP_HEAVY;
       // mutex exit
     }
     loops++;
-    if (max_loops < loops)
+    if (max_loops < loops) {
+      SLEEP_HEAVY;
       (*thread.is_finished) = true;
+    }
   }
 
-  std::cout << "Hello from thread " << thread.id << "! (done)" << std::endl;
+  std::cerr << "Hello from thread " << thread.id << "! (done)" << std::endl;
 
   pthread_exit(nullptr);
 }
@@ -123,41 +151,54 @@ 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) {
+    SLEEP_HEAVY;
     pthread_create(&my_pthreads[tid], NULL,
                    reinterpret_cast<PthreadFun>(thread_task_increment),
                    &thread_data[tid]);
+    SLEEP_HEAVY;
   }
 
-  std::cout << "Threads have been spawned." << std::endl;
+  std::cerr << "Threads have been spawned." << std::endl;
 
   // loop until all threads are done
   for (size_t finished_threads = 0; finished_threads < threads.total_threads;) {
 
+    SLEEP_LIGHT;
     // 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) {
 
+      SLEEP_LIGHT;
       if (threads.wants_mutex[tid_wants]) {
         // in case the mutex isn't used at all
         bool mutex_was_found = false;
 
+        SLEEP_LIGHT;
         // 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_LIGHT;
             // we found who has the mutex!
             mutex_was_found = true;
+            SLEEP_LIGHT;
 
             // is the thread still using the mutex?
             if (!threads.wants_mutex[tid_has]) {
 
+              SLEEP_LIGHT;
               // take the mutex from the thread that has it
               threads.has_mutex[tid_has] = false;
+              SLEEP_LIGHT;
               threads.can_ask_for_mutex[tid_has] = true;
+              SLEEP_HEAVY;
               // give the mutex to the thread that wants it
               threads.can_ask_for_mutex[tid_wants] = false;
+              SLEEP_LIGHT;
               threads.has_mutex[tid_wants] = true;
+              SLEEP_HEAVY;
             }
 
             break; // no need to look at the rest if we found who has the mutex
@@ -166,16 +207,22 @@ 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) {
+          SLEEP_LIGHT;
           threads.has_mutex[tid_wants] = true;
+          SLEEP_LIGHT;
         }
+        SLEEP_LIGHT;
       }
     }
 
     // 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;
+        SLEEP_LIGHT;
+      }
+      SLEEP_LIGHT;
     }
   }
 
@@ -190,10 +237,16 @@ void do_threading(struct thread_group threads) {
 int main(void) {
   struct thread_group mythreads;
 
+  // initialize random (for random sleep amounts)
+  srand(time(NULL));
+
   // the count
   int count = 0;
 
-  std::cout << "Pre: " << DBG_PRINT(count) << std::endl;
+  // expected result
+  const int count_expected = NUM_THREADS * (THREAD_LOOP_COUNT + 1) + count;
+
+  std::cout << "Expected: " << count_expected << std::endl;
 
   mythreads.data = &count;
   mythreads.total_threads = NUM_THREADS;
@@ -201,5 +254,7 @@ int main(void) {
 
   do_threading(mythreads);
 
-  std::cout << "Post: " << DBG_PRINT(count) << std::endl;
+  std::cout << "Got: " << count << std::endl;
+
+  return !(count_expected == count);
 }