fixed readme conflict

1 files changed, 155 insertions, 123 deletions

diff --git a/mthread.cpp b/mthread.cpp
index 796055e..7d1b31f 100644
--- a/mthread.cpp
+++ b/mthread.cpp
@@ -26,11 +26,12 @@ mthread::mthread(
   histogram = g_histogram;
   step = (c_max - c_min) / complex<double>(image.height(), image.width());
   my_thread = NULL;
+  status.status_lock.lock();
 }
 
 void mthread::dispatch() {
   if((my_thread) && (my_thread->joinable())) delete my_thread;
-  my_thread = new thread([this] {render();}); 
+  my_thread = new thread([this] {run();}); 
 }
 
 
@@ -46,151 +47,182 @@ void mthread::join() {
   if((my_thread) && (my_thread->joinable())) my_thread->join();
 }
 
-
-void mthread::render() {
-  uint32_t image_width = image.width();
-  unsigned int iter;
+bool mthread::find_work() {
   unsigned int worker, workers_finished;
   uint32_t loads[worker_cnt];
-  double pixel_value;
-  complex<double> c, a;
   struct mthread_status *peer_status;
   struct mthread_divinfo divinfo;
-
+  workers_finished = 0;
   unique_lock<mutex> ack;
-  unique_lock<mutex> syn_ack;
 
-
-  status.status_lock.lock();
-  status.searching = false;
-  status.share_finished = false;
-  status.div_syn = false;
-  status.div_error = false;
+  status.status_lock.lock(); 
+  status.searching = true;
+  status.share_finished = true;
   status.status_lock.unlock();
 
+  for(worker = 0; worker < worker_cnt; worker++) {
+    //lock other worker so we can request from them
+    peer_status = &workers[worker]->status; 
+    peer_status->status_lock.lock();
 
-  y_min = 0;
-  y_max = image.height();
-
-
+    //if they're done, we remember that to see if we exit
+    if((peer_status->share_finished) && (worker != id)) {
+      workers_finished++;
+    }
+    
+    /** The reason why we have this bit in code twice is to prevent race conditions.
+     *  To add the potential canidate worker to our list to be sorted, 
+     *  we need to make sure it's not currently being divided (true if div_syn is set). 
+     *  Since we'll need to check the same later 
+     *  when we actually request to split it's workload, 
+     *  we might as well narrow it down and check everything else.
+     *  **/
+    if((worker == id) || 
+        (peer_status->searching) || (peer_status->div_syn) || 
+        (peer_status->row_load < min_lines)) {
+      loads[worker] = 0;
+      peer_status->status_lock.unlock();
+      continue;
+    }
 
+    //finally, if they're valid, write them down
+    loads[worker] = peer_status->row_load;
+    peer_status->status_lock.unlock();
+  }
+  //exit if all workers are finished
+  if(workers_finished >= worker_cnt - 1) {
+    return false;
+  }
+  //then we look over and pick our canidates
   for(;;) {
-    //thread is actively rendering
-    for(on_y = y_min; on_y < y_max; on_y++) {
-      progress++;
-      status.status_lock.lock();
-      status.row_load = y_max - on_y;
-      if(status.div_syn) {
-
-        status.div_error = status.row_load <= min_lines;
-
-        if(status.div_error) {
-          status.ack_lk.unlock();
-          status.msg_notify.notify_all();
-        }
-        else {
-          syn_ack = unique_lock<mutex>(status.syn_ack_lk);
-          status.ack_lk.unlock();
-          status.msg_notify.notify_all();
-          status.msg_notify.wait(syn_ack);
-          status.row_load = y_max - on_y;
-          syn_ack.unlock();
-          //new x/y min/max is ajusted by other thread, we can continue as normal.
-        }
-      }
-      status.status_lock.unlock(); 
-
-      for(on_x = x_min; on_x < x_max; on_x++) {
-      c = (step * complex<double>(on_x,on_y)) + c_min;
-      a = 0;
-        for(iter = 0; iter < max_iter; iter++) {
-          if(abs(a) >= inf_cutoff) break;
-          a = a*a + c;
-        }
-        if(iter >= max_iter) {
-          iter = 0;
-          vmap[(on_y * image_width) + on_x] = 0;
-        }
-        else {
-          pixel_value = (iter + 1) - (log((log(pow(abs(a), 2.0)) / 2.0) / log(2.0))); 
-          vmap[(on_y * image_width) + on_x] = pixel_value;
-          histogram[(int)pixel_value]++;
-        }
-      }
+    //find the worker who has the biggest workload
+    worker = distance(loads, max_element(loads, &loads[worker_cnt]));
+    if(!loads[worker]) return true; //we have found a worker; distance is 0
+    peer_status = &workers[worker]->status;
+    peer_status->status_lock.lock();
+
+    //re-check to see if canidate is valid (may have changed since added and sorted). 
+    //If you're wondering why we're doing this bit again, see comment before first time.
+    if((peer_status->searching) || (peer_status->div_syn) || 
+        (peer_status->row_load < min_lines)) {
+      loads[worker] = 0;
+      peer_status->status_lock.unlock();
+      continue;
+    }
+    //ack: ask peer to devide
+    ack = unique_lock<mutex>(peer_status->ack_lk);
+    peer_status->div_syn = true;
+    peer_status->status_lock.unlock();
+    //when they reset it, they've acknowlaged and have set appropriate messages
+    peer_status->msg_notify.wait(ack);
+    ack.unlock();
+    //area is too small to divide reliably
+    if(peer_status->div_error) {
+      loads[worker] = 0;
+      peer_status->status_lock.lock();
+      peer_status->div_error = false;
+      peer_status->div_syn = false;
+      peer_status->status_lock.unlock();
+      continue;
     }
 
+    //otherwise, we modify their struct for them to split their workload
+    divinfo = workers[worker]->divide();
+    peer_status->syn_ack_lk.unlock();
 
-    //thread is now searching for work
-    
-    /** 2022 comment:
-     * this state should have been moved to a seperate function to allow rendering methods to differ
-     * from inherited mthreads without needing to reimpliment searching **/
-    status.status_lock.lock(); 
-    status.searching = true;
-    status.share_finished = true;
+    //tell them we're done modifying
+    peer_status->msg_notify.notify_all();
+
+    //set our own stuff
+    y_min = divinfo.y_min;
+    y_max = divinfo.y_max;
+    x_min = divinfo.x_min;
+    x_max = divinfo.x_max;
+
+    //update our status
+    status.status_lock.lock();
+    status.searching = false;
     status.status_lock.unlock();
+    return true;
+  }
+  return true;
+}
+
+//makes sure no one is asking for work from us
+void mthread::check_work_request() {
+  unique_lock<mutex> syn_ack;
+
+  status.status_lock.lock();
+  status.row_load = y_max - on_y;
+  //check if anyone's asking us to divide
+  if(status.div_syn) {
+    status.div_error = status.row_load <= min_lines;
+    if(status.div_error) {
+      status.ack_lk.unlock();
+      status.msg_notify.notify_all();
+    }
+    else {
+      syn_ack = unique_lock<mutex>(status.syn_ack_lk);
+      status.ack_lk.unlock();
+      status.msg_notify.notify_all();
+      status.msg_notify.wait(syn_ack);
+      status.row_load = y_max - on_y;
+      syn_ack.unlock();
+      //new x/y min/max is ajusted by other thread, we can continue as normal.
+    }
+  }
+  status.status_lock.unlock(); 
+}
 
-    while(status.searching) {
-      workers_finished = 0;
-      for(worker = 0; worker < worker_cnt; worker++) {
-        peer_status = &workers[worker]->status; 
-        peer_status->status_lock.lock();
-
-        if((peer_status->share_finished) && (worker != id)) {
-          workers_finished++;
-        }
-        if((worker == id) || 
-            (peer_status->searching) || (peer_status->div_syn) || (peer_status->row_load < min_lines)) {
-          loads[worker] = 0;
-          peer_status->status_lock.unlock();
-          continue;
-        }
-        loads[worker] = peer_status->row_load;
-        peer_status->status_lock.unlock();
+//renders area
+void mthread::render_area() { 
+  uint32_t image_width = image.width();
+  unsigned int iter;
+  complex<double> c, z; 
+  double pixel_value;
+
+  /** pixel is drawn based on if/how many itertions it takes to get to infinity 
+   * while computing z^2+c. **/
+
+  for(on_y = y_min; on_y < y_max; on_y++) {
+    progress++;
+    check_work_request();
+    for(on_x = x_min; on_x < x_max; on_x++) {
+    c = (step * complex<double>(on_x,on_y)) + c_min;
+    z = 0;
+      for(iter = 0; iter < max_iter; iter++) {
+        if(abs(z) >= inf_cutoff) break;
+        z = z*z + c;
       }
-      if(workers_finished >= worker_cnt - 1) {
-        return;
+      if(iter >= max_iter) {
+        iter = 0;
+        vmap[(on_y * image_width) + on_x] = 0;
       }
-      for(;;) {
-        worker = distance(loads, max_element(loads, &loads[worker_cnt]));
-        if(!loads[worker]) break;
-        peer_status = &workers[worker]->status;
-        peer_status->status_lock.lock();
-        if((peer_status->searching) || (peer_status->div_syn) || (peer_status->row_load < min_lines)) {
-          loads[worker] = 0;
-          peer_status->status_lock.unlock();
-          continue;
-        }
-        ack = unique_lock<mutex>(peer_status->ack_lk);
-        peer_status->div_syn = true;
-        peer_status->status_lock.unlock();
-        peer_status->msg_notify.wait(ack);
-        ack.unlock();
-        if(peer_status->div_error) {
-          loads[worker] = 0;
-          peer_status->status_lock.lock();
-          peer_status->div_error = false;
-          peer_status->div_syn = false;
-          peer_status->status_lock.unlock();
-          continue;
-        }
-
-        divinfo = workers[worker]->divide();
-        peer_status->syn_ack_lk.unlock();
-        peer_status->msg_notify.notify_all();
-        y_min = divinfo.y_min;
-        y_max = divinfo.y_max;
-        x_min = divinfo.x_min;
-        x_max = divinfo.x_max;
-        status.status_lock.lock();
-        status.searching = false;
-        status.status_lock.unlock();
-        break;
+      else {
+        pixel_value = (iter + 1) - (log((log(pow(abs(z), 2.0)) / 2.0) / log(2.0))); 
+        vmap[(on_y * image_width) + on_x] = pixel_value;
+        histogram[(int)pixel_value]++;
       }
     }
   }
 }
 
+//alternates states of finding work work and rendering
+void mthread::run() {
+  //locks in initilizer
+  status.searching = false;
+  status.share_finished = false;
+  status.div_syn = false;
+  status.div_error = false;
+  status.status_lock.unlock();
+
+  do {
+    render_area();
+  } while (find_work());
+
+}
+
+
 struct mthread_divinfo mthread::divide() {
   struct mthread_divinfo ret;
   ret.x_min = x_min;