pcbnew: Remove OpenMP

OpenMP is not available for macos, so moving to a std::threads
implementation brings platforms into shared code.

This also reduces the OpenMP overhead when computing connectivity and
ratsnests.

Fixes: lp:1780130
* https://bugs.launchpad.net/kicad/+bug/1780130

(cherry picked from commit c0f067bf90)

pcbnew/connectivity_algo.cpp

@@ -33,9 +33,6 @@
 #include <profile.h>
 #endif
 
-#ifdef USE_OPENMP
-#include <omp.h>
-#endif /* USE_OPENMP */
 
 using namespace std::placeholders;
 
@@ -324,7 +321,6 @@ void CN_CONNECTIVITY_ALGO::searchConnections()
 
 #ifdef PROFILE
     garbage_collection.Show();
-    PROF_COUNTER search_cnt( "search-connections" );
     PROF_COUNTER search_basic( "search-basic" );
 #endif
 
@@ -333,49 +329,63 @@ void CN_CONNECTIVITY_ALGO::searchConnections()
         m_progressReporter->SetMaxProgress( m_itemList.IsDirty() ? m_itemList.Size() : 0 );
     }
 
-#ifdef USE_OPENMP
-    #pragma omp parallel num_threads( std::max( omp_get_num_procs(), 2 ) )
+    if( m_itemList.IsDirty() )
     {
-        if( omp_get_thread_num() == 0 && m_progressReporter )
-            m_progressReporter->KeepRefreshing( true );
-#endif
+        std::atomic<int> nextItem( 0 );
+        std::atomic<size_t> threadsFinished( 0 );
+        size_t numDirty = std::count_if( m_itemList.begin(), m_itemList.end(), [] ( CN_ITEM* aItem )
+                { return aItem->Dirty(); } );
 
-        if( m_itemList.IsDirty() )
+        size_t parallelThreadCount = std::min<size_t>(
+                std::max<size_t>( std::thread::hardware_concurrency(), 2 ),
+                numDirty );
+
+        for( size_t ii = 0; ii < parallelThreadCount; ++ii )
         {
-#ifdef USE_OPENMP
-            #pragma omp parallel for
-#endif
-            for( int i = 0; i < m_itemList.Size(); i++ )
+            std::thread t = std::thread( [&nextItem, &threadsFinished, this]()
             {
-                auto item = m_itemList[i];
-                if( item->Dirty() )
+                for( int i = nextItem.fetch_add( 1 );
+                         i < m_itemList.Size();
+                         i = nextItem.fetch_add( 1 ) )
                 {
-                    CN_VISITOR visitor( item, &m_listLock );
-                    m_itemList.FindNearby( item, visitor );
+                    auto item = m_itemList[i];
+                    if( item->Dirty() )
+                    {
+                        CN_VISITOR visitor( item, &m_listLock );
+                        m_itemList.FindNearby( item, visitor );
+                    }
+
+                    if( m_progressReporter )
+                        m_progressReporter->AdvanceProgress();
                 }
 
-                if( m_progressReporter )
-                    m_progressReporter->AdvanceProgress();
-            }
+                threadsFinished++;
+            } );
+
+            t.detach();
         }
 
+        // Finalize the connectivity threads
+        while( threadsFinished < parallelThreadCount )
+        {
+            if( m_progressReporter )
+                m_progressReporter->KeepRefreshing();
+
+            // This routine is called every click while routing so keep the sleep time minimal
+            std::this_thread::sleep_for( std::chrono::milliseconds( 1 ) );
+        }
+    }
+
 #ifdef PROFILE
         search_basic.Show();
 #endif
 
-#ifdef USE_OPENMP
-    }
-#endif
-
     m_itemList.ClearDirtyFlags();
 
 #ifdef CONNECTIVITY_DEBUG
     printf("Search end\n");
 #endif
 
-#ifdef PROFILE
-    search_cnt.Show();
-#endif
 }
 
 

pcbnew/connectivity_data.cpp

@@ -21,18 +21,17 @@
  * or you may write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
  */
+
 #ifdef PROFILE
 #include <profile.h>
 #endif
 
+#include <thread>
+
 #include <connectivity_data.h>
 #include <connectivity_algo.h>
 #include <ratsnest_data.h>
 
-#ifdef USE_OPENMP
-#include <omp.h>
-#endif /* USE_OPENMP */
-
 CONNECTIVITY_DATA::CONNECTIVITY_DATA()
 {
     m_connAlgo.reset( new CN_CONNECTIVITY_ALGO );
@@ -87,31 +86,40 @@ void CONNECTIVITY_DATA::Build( const std::vector<BOARD_ITEM*>& aItems )
 
 void CONNECTIVITY_DATA::updateRatsnest()
 {
-    int lastNet = m_connAlgo->NetCount();
-
     #ifdef PROFILE
     PROF_COUNTER rnUpdate( "update-ratsnest" );
     #endif
 
-    int i;
+    size_t numDirty = std::count_if( m_nets.begin() + 1, m_nets.end(), [] ( RN_NET* aNet )
+            { return aNet->IsDirty(); } );
 
-    #ifdef USE_OPENMP
-        #pragma omp parallel shared(lastNet) private(i)
-    {
-        #pragma omp for schedule(guided, 1)
-    #else /* USE_OPENMP */
-    {
-    #endif
+    std::atomic<size_t> nextNet( 1 );
+    std::atomic<size_t> threadsFinished( 0 );
 
-        // Start with net number 1, as 0 stands for not connected
-        for( i = 1; i < lastNet; ++i )
+    // We don't want to spin up a new thread for fewer than two nets (overhead costs)
+    size_t parallelThreadCount = std::min<size_t>(
+            std::max<size_t>( std::thread::hardware_concurrency(), 2 ),
+            numDirty / 2 );
+
+    for( size_t ii = 0; ii < parallelThreadCount; ++ii )
+    {
+        std::thread t = std::thread( [&nextNet, &threadsFinished, this]()
         {
-            if( m_nets[i]->IsDirty() )
+            for( size_t i = nextNet.fetch_add( 1 ); i < m_nets.size(); i = nextNet.fetch_add( 1 ) )
             {
-                m_nets[i]->Update();
+                if( m_nets[i]->IsDirty() )
+                    m_nets[i]->Update();
             }
-        }
-    }          /* end of parallel section */
+
+            threadsFinished++;
+        } );
+
+        t.detach();
+    }
+
+    // Finalize the ratsnest threads
+    while( threadsFinished < parallelThreadCount )
+        std::this_thread::sleep_for( std::chrono::milliseconds( 1 ) );
 
     #ifdef PROFILE
     rnUpdate.Show();

qa/polygon_triangulation/test_polygon_triangulation.cpp

@@ -32,6 +32,7 @@
 #include <class_zone.h>
 #include <profile.h>
 
+#include <thread>
 #include <unordered_set>
 #include <utility>