Cache the contents of systemlib.php for use by the debugger, if debugging.

Instead of calling get_systemlib every time the debugger client needs to list source from systemlib.php, use a cached copy of the source string. Only do this if debugging is enabled.

hphp/runtime/base/program_functions.cpp

@@ -1199,7 +1199,9 @@ string get_systemlib(string* hhas) {
   ifs.seekg(desc.m_start, std::ios::beg);
   std::unique_ptr<char[]> data(new char[desc.m_len]);
   ifs.read(data.get(), desc.m_len);
-  return systemlib_split(string(data.get(), desc.m_len), hhas);
+  string ret = systemlib_split(string(data.get(), desc.m_len), hhas);
+  if (RuntimeOption::EnableDebugger) SystemLib::s_source = ret;
+  return ret;
 }
 
 ///////////////////////////////////////////////////////////////////////////////

hphp/runtime/debugger/cmd/cmd_list.cpp

@@ -350,7 +350,7 @@ bool CmdList::onServer(DebuggerProxy &proxy) {
   }
   RuntimeOption::WarningFrequency = savedWarningFrequency;
   if (!m_code && m_file == "systemlib.php") {
-    m_code = get_systemlib();
+    m_code = SystemLib::s_source;
   }
   return proxy.sendToClient((DebuggerCommand*)this);
 }

hphp/system/lib/systemlib.cpp

@@ -33,6 +33,7 @@ namespace HPHP {
   }
 
 bool SystemLib::s_inited = false;
+string SystemLib::s_source = "";
 HPHP::Unit* SystemLib::s_unit = nullptr;
 HPHP::Unit* SystemLib::s_hhas_unit = nullptr;
 HPHP::Unit* SystemLib::s_nativeFuncUnit = nullptr;

hphp/system/lib/systemlib.h

@@ -68,6 +68,7 @@ namespace Eval {
 class SystemLib {
  public:
   static bool s_inited;
+  static string s_source;
   static HPHP::Unit* s_unit;
   static HPHP::Unit* s_hhas_unit;
   static HPHP::Unit* s_nativeFuncUnit;