Use UI lock for yielding

common/nextpnr.h

@@ -318,6 +318,11 @@ struct BaseCtx
     std::mutex mutex;
     pthread_t mutex_owner;
 
+    // Lock to be taken by UI when wanting to access context - the yield()
+    // method will lock/unlock it when its' released the main mutex to make
+    // sure the UI is not starved.
+    std::mutex ui_mutex;
+
     // ID String database.
     mutable std::unordered_map<std::string, int> *idstring_str_to_idx;
     mutable std::vector<const std::string *> *idstring_idx_to_str;
@@ -353,12 +358,31 @@ struct BaseCtx
         mutex.unlock();
     }
 
-    // TODO(q3k): get rid of this hack
+    // Must be called by the UI before rendering data. This lock will be
+    // prioritized when processing code calls yield().
+    void lock_ui(void)
+    {
+        ui_mutex.lock();
+        mutex.lock();
+    }
+
+    void unlock_ui(void)
+    {
+        mutex.unlock();
+        ui_mutex.unlock();
+    }
+
+    // Yield to UI by unlocking the main mutex, flashing the UI mutex and
+    // relocking the main mutex. Call this when you're performing a
+    // long-standing action while holding a lock to let the UI show
+    // visualization updates.
+    // Must be called with the main lock taken.
     void yield(void)
     {
-        for (int i = 0; i < 10; i++) {
-            pthread_yield();
-        }
+        unlock();
+        ui_mutex.lock();
+        ui_mutex.unlock();
+        lock();
     }
 
     IdString id(const std::string &s) const { return IdString(this, s); }

common/placer1.cc

@@ -156,8 +156,6 @@ class SAPlacer
 
         // Main simulated annealing loop
         for (int iter = 1;; iter++) {
-            ctx->yield();
-            ctx->lock();
             n_move = n_accept = 0;
             improved = false;
 
@@ -242,7 +240,9 @@ class SAPlacer
                 metrics[net.first] = wl;
                 curr_metric += wl;
             }
-            ctx->unlock();
+
+            // Let the UI show visualization updates.
+            ctx->yield();
         }
         // Final post-pacement validitiy check
         ctx->lock();

common/router1.cc

@@ -495,8 +495,6 @@ bool router1(Context *ctx)
 #endif
                 return false;
             }
-            ctx->yield();
-            ctx->lock();
 
             iterCnt++;
             if (ctx->verbose)
@@ -533,9 +531,11 @@ bool router1(Context *ctx)
                     ripupQueue.insert(net_name);
                 }
 
-                if ((ctx->verbose || iterCnt == 1) && !printNets && (netCnt % 100 == 0))
+                if ((ctx->verbose || iterCnt == 1) && !printNets && (netCnt % 100 == 0)) {
                     log_info("  processed %d nets. (%d routed, %d failed)\n", netCnt, netCnt - int(ripupQueue.size()),
                              int(ripupQueue.size()));
+                    ctx->yield();
+                }
             }
 
             int normalRouteCnt = netCnt - int(ripupQueue.size());
@@ -596,8 +596,10 @@ bool router1(Context *ctx)
 
                     ripCnt += router.rippedNets.size();
 
-                    if ((ctx->verbose || iterCnt == 1) && !printNets && (netCnt % 100 == 0))
+                    if ((ctx->verbose || iterCnt == 1) && !printNets && (netCnt % 100 == 0)) {
                         log_info("  routed %d nets, ripped %d nets.\n", netCnt, ripCnt);
+                        ctx->yield();
+                    }
                 }
 
                 if ((ctx->verbose || iterCnt == 1) && (netCnt % 100 != 0))
@@ -626,7 +628,7 @@ bool router1(Context *ctx)
             if (iterCnt == 8 || iterCnt == 16 || iterCnt == 32 || iterCnt == 64 || iterCnt == 128)
                 ripup_penalty += ctx->getRipupDelayPenalty();
 
-            ctx->unlock();
+            ctx->yield();
         }
 
         log_info("routing complete after %d iterations.\n", iterCnt);

gui/fpgaviewwidget.cc

@@ -426,7 +426,7 @@ void FPGAViewWidget::renderLines(void)
     if (ctx_ == nullptr)
         return;
 
-    ctx_->lock();
+    ctx_->lock_ui();
 
     // For now, collapse any decal changes into change of all decals.
     // TODO(q3k): fix this
@@ -475,7 +475,7 @@ void FPGAViewWidget::renderLines(void)
             groupDecals.push_back(ctx_->getGroupDecal(group));
         }
     }
-    ctx_->unlock();
+    ctx_->unlock_ui();
 
     rendererArgsLock_.lock();
     auto selectedItems = rendererArgs_->selectedItems;