Fix single-threaded loads/connectivity

We cannot set thread counts to hardware_concurrency()-1 without
considering that single core machines will get a thread count of 0.

eeschema/symbol_async_loader.cpp

@@ -39,7 +39,7 @@ SYMBOL_ASYNC_LOADER::SYMBOL_ASYNC_LOADER( const std::vector<wxString>& aNickname
         m_canceled( false )
 {
     wxASSERT( m_table );
-    m_threadCount = std::max<size_t>( 1, std::thread::hardware_concurrency() - 1 );
+    m_threadCount = std::max<size_t>( 1, std::thread::hardware_concurrency() );
 
     m_returns.resize( m_threadCount );
 }

pcbnew/connectivity/connectivity_data.cpp

@@ -143,7 +143,7 @@ void CONNECTIVITY_DATA::updateRatsnest()
             } );
 
     // We don't want to spin up a new thread for fewer than 8 nets (overhead costs)
-    size_t parallelThreadCount = std::min<size_t>( std::thread::hardware_concurrency() - 1,
+    size_t parallelThreadCount = std::min<size_t>( std::thread::hardware_concurrency(),
                                                    ( dirty_nets.size() + 7 ) / 8 );
 
     std::atomic<size_t> nextNet( 0 );
@@ -158,7 +158,7 @@ void CONNECTIVITY_DATA::updateRatsnest()
                 return 1;
             };
 
-    if( parallelThreadCount == 1 )
+    if( parallelThreadCount <= 1 )
     {
         update_lambda();
     }

pcbnew/drc/drc_test_provider_connectivity.cpp

@@ -79,6 +79,8 @@ bool DRC_TEST_PROVIDER_CONNECTIVITY::Run()
 
     std::shared_ptr<CONNECTIVITY_DATA> connectivity = board->GetConnectivity();
 
+    std::lock_guard<KISPINLOCK> lock( connectivity->GetLock() );
+
     // Rebuild just in case. This really needs to be reliable.
     connectivity->Clear();
     connectivity->Build( board, m_drcEngine->GetProgressReporter() );
@@ -149,7 +151,6 @@ bool DRC_TEST_PROVIDER_CONNECTIVITY::Run()
     if( !reportPhase( _( "Checking net connections..." ) ) )
         return false;   // DRC cancelled
 
-    connectivity->RecalculateRatsnest();
     std::vector<CN_EDGE> edges;
     connectivity->GetUnconnectedEdges( edges );
 
@@ -191,4 +192,4 @@ std::set<DRC_CONSTRAINT_T> DRC_TEST_PROVIDER_CONNECTIVITY::GetConstraintTypes()
 namespace detail
 {
 static DRC_REGISTER_TEST_PROVIDER<DRC_TEST_PROVIDER_CONNECTIVITY> dummy;
-}
+}

pcbnew/pcb_draw_panel_gal.cpp

@@ -185,7 +185,7 @@ void PCB_DRAW_PANEL_GAL::DisplayBoard( BOARD* aBoard, PROGRESS_REPORTER* aReport
     auto zones = aBoard->Zones();
     std::atomic<size_t> next( 0 );
     std::atomic<size_t> count_done( 0 );
-    size_t parallelThreadCount = std::max<size_t>( std::thread::hardware_concurrency() - 1, 2 );
+    size_t parallelThreadCount = std::max<size_t>( std::thread::hardware_concurrency(), 2 );
 
     for( size_t ii = 0; ii < parallelThreadCount; ++ii )
     {