From 54adb84e275b8005b92d31268f55dd35f4534b10 Mon Sep 17 00:00:00 2001
From: Matthias Koefferlein <matthias@koefferlein.de>
Date: Sat, 29 Dec 2018 01:04:48 +0100
Subject: [PATCH] WIP: locking of netlist for better performance.

---
 src/db/db/dbNetlist.cc              | 34 ++++++++++++++++----
 src/db/db/dbNetlist.h               | 50 +++++++++++++++++++++++++++++
 src/db/unit_tests/dbNetlistTests.cc | 10 ++++++
 3 files changed, 88 insertions(+), 6 deletions(-)

diff --git a/src/db/db/dbNetlist.cc b/src/db/db/dbNetlist.cc
index 0e954a4e4..0b6631132 100644
--- a/src/db/db/dbNetlist.cc
+++ b/src/db/db/dbNetlist.cc
@@ -1129,13 +1129,13 @@ size_t DeviceClass::terminal_id_for_name (const std::string &name) const
 //  Netlist class implementation
 
 Netlist::Netlist ()
-  : m_valid_topology (false)
+  : m_valid_topology (false), m_lock_count (0)
 {
   m_circuits.changed ().add (this, &Netlist::invalidate_topology);
 }
 
 Netlist::Netlist (const Netlist &other)
-  : m_valid_topology (false)
+  : m_valid_topology (false), m_lock_count (0)
 {
   operator= (other);
   m_circuits.changed ().add (this, &Netlist::invalidate_topology);
@@ -1173,11 +1173,16 @@ Netlist &Netlist::operator= (const Netlist &other)
 void Netlist::invalidate_topology ()
 {
   if (m_valid_topology) {
+
     m_valid_topology = false;
-    m_top_circuits = 0;
-    m_top_down_circuits.clear ();
-    m_child_circuits.clear ();
-    m_parent_circuits.clear ();
+
+    if (m_lock_count == 0) {
+      m_top_circuits = 0;
+      m_top_down_circuits.clear ();
+      m_child_circuits.clear ();
+      m_parent_circuits.clear ();
+    }
+
   }
 }
 
@@ -1195,6 +1200,8 @@ void Netlist::validate_topology ()
 {
   if (m_valid_topology) {
     return;
+  } else if (m_lock_count > 0) {
+    return;
   }
 
   m_child_circuits.clear ();
@@ -1295,6 +1302,21 @@ void Netlist::validate_topology ()
   m_valid_topology = true;
 }
 
+void Netlist::lock ()
+{
+  if (m_lock_count == 0) {
+    validate_topology ();
+  }
+  ++m_lock_count;
+}
+
+void Netlist::unlock ()
+{
+  if (m_lock_count > 0) {
+    --m_lock_count;
+  }
+}
+
 const tl::vector<Circuit *> &Netlist::child_circuits (Circuit *circuit)
 {
   if (! m_valid_topology) {
diff --git a/src/db/db/dbNetlist.h b/src/db/db/dbNetlist.h
index cbdedddf8..cf1016e97 100644
--- a/src/db/db/dbNetlist.h
+++ b/src/db/db/dbNetlist.h
@@ -1806,6 +1806,30 @@ public:
    */
   void clear ();
 
+  /**
+   *  @brief Starts a sequence of operations during which topology updates are not desired
+   *
+   *  If the hierarchy is modified, the topology information (top-down order, children
+   *  and parent information) may be recomputed frequently. This may cause performance issues
+   *  and may not be desired.
+   *
+   *  Calling this method will bring the netlist into a state in which updates on the
+   *  list will not happen. Using "unlock" will end this state.
+   *
+   *  "lock" and "unlock" are incremental and can be nested. Use "NetlistLocker" for safe locking
+   *  and unlocking.
+   *
+   *  Before lock, the state will be validated, so inside the locked operation, the topology
+   *  information will be valid with respect to the initial state.
+   */
+  void lock ();
+
+  /**
+   *  @brief Ends a sequence of operations during which topology updates are not desired
+   *  See "lock" for more details.
+   */
+  void unlock ();
+
   /**
    *  @brief Adds a circuit to this netlist
    *
@@ -1974,6 +1998,7 @@ private:
   circuit_list m_circuits;
   device_class_list m_device_classes;
   bool m_valid_topology;
+  int m_lock_count;
   tl::vector<Circuit *> m_top_down_circuits;
   tl::vector<tl::vector<Circuit *> > m_child_circuits;
   tl::vector<tl::vector<Circuit *> > m_parent_circuits;
@@ -1986,6 +2011,31 @@ private:
   const tl::vector<Circuit *> &parent_circuits (Circuit *circuit);
 };
 
+/**
+ *  @brief A helper class using RAII for safe locking/unlocking
+ */
+class DB_PUBLIC NetlistLocker
+{
+public:
+  NetlistLocker (Netlist *netlist)
+    : mp_netlist (netlist)
+  {
+    if (mp_netlist.get ()) {
+      mp_netlist->lock ();
+    }
+  }
+
+  ~NetlistLocker ()
+  {
+    if (mp_netlist.get ()) {
+      mp_netlist->unlock ();
+    }
+  }
+
+private:
+  tl::weak_ptr<Netlist> mp_netlist;
+};
+
 }
 
 #endif
diff --git a/src/db/unit_tests/dbNetlistTests.cc b/src/db/unit_tests/dbNetlistTests.cc
index 3edfe1503..a25147743 100644
--- a/src/db/unit_tests/dbNetlistTests.cc
+++ b/src/db/unit_tests/dbNetlistTests.cc
@@ -902,9 +902,19 @@ TEST(12_NetlistTopology)
   EXPECT_EQ (td2string (nl.get ()), "c1,c2");
   EXPECT_EQ (bu2string (nl.get ()), "c2,c1");
 
+  std::auto_ptr<db::NetlistLocker> locker (new db::NetlistLocker (nl.get ()));
+
   db::Circuit *c3 = new db::Circuit ();
   c3->set_name ("c3");
   nl->add_circuit (c3);
+
+  //  because we locked, it did not get updated:
+  EXPECT_EQ (nl->top_circuit_count (), size_t (2));
+  EXPECT_EQ (td2string (nl.get ()), "c1,c2");
+  EXPECT_EQ (bu2string (nl.get ()), "c2,c1");
+  locker.reset (0);
+
+  //  after removing the lock, it's updated
   EXPECT_EQ (nl->top_circuit_count (), size_t (3));
   EXPECT_EQ (td2string (nl.get ()), "c1,c2,c3");
   EXPECT_EQ (bu2string (nl.get ()), "c3,c2,c1");