Make reference counting thread safe

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/util/name.cpp

@@ -7,42 +7,37 @@ Author: Leonardo de Moura
 #include <cstring>
 #include "name.h"
 #include "debug.h"
+#include "rc.h"
 
 namespace lean {
 
 constexpr char const * anonymous_str = "[anonymous]";
 
 struct name::imp {
+    MK_LEAN_RC()
     bool     m_is_string;
-    unsigned m_rc;
     imp *    m_prefix;
     union {
         char * m_str;
         unsigned m_k;
     };
     
-    void inc_ref() { m_rc++; }
-
-    void dec_ref() { 
+    void dealloc() {
         imp * curr = this;
-        while (curr) {
-            lean_assert(curr->m_rc > 0); 
-            curr->m_rc--; 
-            if (curr->m_rc == 0) {
+        while (true) {
+            lean_assert(curr->get_rc() == 0);
             imp * p = curr->m_prefix;
             if (curr->m_is_string)
                 delete[] reinterpret_cast<char*>(curr);
             else
                 delete curr;
             curr = p;
-            }
-            else {
-                curr = 0;
-            }
+            if (!curr || !curr->dec_ref_core())
+                break;
         }
     }
 
-    imp(bool s, imp * p):m_is_string(s), m_rc(1), m_prefix(p) { if (p) p->inc_ref(); }
+    imp(bool s, imp * p):m_rc(1), m_is_string(s), m_prefix(p) { if (p) p->inc_ref(); }
 
     static void display_core(std::ostream & out, char const * sep, imp * p) {
         lean_assert(p != nullptr);

src/util/rc.h

@@ -0,0 +1,28 @@
+/*
+Copyright (c) 2013 Microsoft Corporation. All rights reserved. 
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura 
+*/
+#pragma once
+
+// Goodies for reference counting
+
+#include "debug.h"
+
+#ifdef LEAN_THREAD_UNSAFE_REF_COUNT
+#define MK_LEAN_RC()                                                    \
+unsigned m_rc;                                                          \
+unsigned get_rc() const { return m_rc; }                                \
+void inc_ref() { m_rc++; }                                              \
+bool dec_ref_core() { lean_assert(get_rc() > 0);  m_rc--; return m_rc == 0; } \
+void dec_ref() { if (dec_ref_core()) dealloc(); }
+#else
+#include <atomic>
+#define MK_LEAN_RC()                                                    \
+std::atomic<unsigned> m_rc;                                             \
+unsigned get_rc() const { return std::atomic_load(&m_rc); }             \
+void inc_ref() { std::atomic_fetch_add_explicit(&m_rc, 1u, std::memory_order_relaxed); } \
+bool dec_ref_core() { lean_assert(get_rc() > 0); return std::atomic_fetch_sub_explicit(&m_rc, 1u, std::memory_order_relaxed) == 1u; } \
+void dec_ref() { if (dec_ref_core()) dealloc(); }
+#endif