adding rlimit resource limit facility to provide platform and architecture independent method for canceling activities

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/util/rlimit.cpp

@@ -0,0 +1,55 @@
+/*++
+Copyright (c) 2015 Microsoft Corporation
+
+Module Name:
+
+    rlimit.cpp
+
+Abstract:
+
+    Resource limit container.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2015-09-28
+
+Revision History:
+
+--*/
+#include "rlimit.h"
+
+reslimit::reslimit():
+    m_count(0),
+    m_limit(UINT_MAX) {
+}
+
+unsigned reslimit::count() const {
+    return m_count;
+}
+
+bool reslimit::inc() {
+    ++m_count;
+    return m_count <= m_limit;
+}
+
+bool reslimit::inc(unsigned offset) {
+    m_count += offset;
+    return m_count <= m_limit;
+}
+
+void reslimit::push(unsigned delta_limit) {
+    unsigned new_limit = UINT_MAX;
+    if (delta_limit > 0 && delta_limit + m_count > m_count) {
+        new_limit = delta_limit + m_count;
+    }
+    m_limits.push_back(m_limit);
+    m_limit = std::min(new_limit, m_limit);
+}
+
+void reslimit::pop() {
+    if (m_count > m_limit) {
+        m_count = m_limit;
+    }
+    m_limit = m_limits.back();
+    m_limits.pop_back();
+}