Speed up NativeProcessLinux::GetLoadedModuleFileSpec

[labath]

Summary

GetLoadedModuleFileSpec was reading /proc/pid/maps character by character, which was very slow,
since we do that for every shared library, which android tends to have a lot. Switching to
ProcFileReader saves us about 0.4 seconds in attach time.

[tberghammer]

LGTM

Thanks for doing it. I planed to do it for a long time as a cleanup, but haven't expected it to have any effect on attach speed. If you still aren't happy with the parsing speed you can possibly cache the the content of /proc/<pid>/maps in memory for the time the process is stopped.

[labath]

Sounds like a good idea. That would help us a lot with qMemoryRegionInfo packets as well. I'll look into that.

source/Plugins/Process/Linux/NativeProcessLinux.cpp

NativeProcessLinux::FixupBreakpointPCAsNeeded (NativeThreadProtocolSP &thread_sp)
     }
 
     return error;
 }
 
 Error
 NativeProcessLinux::GetLoadedModuleFileSpec(const char* module_path, FileSpec& file_spec)
 {
-    char maps_file_name[32];
-    snprintf(maps_file_name, sizeof(maps_file_name), "/proc/%" PRIu64 "/maps", GetID());
-
-    FileSpec maps_file_spec(maps_file_name, false);
-    if (!maps_file_spec.Exists()) {
-        file_spec.Clear();
-        return Error("/proc/%" PRIu64 "/maps file doesn't exists!", GetID());
-    }
-
     FileSpec module_file_spec(module_path, true);
 
-    std::ifstream maps_file(maps_file_name);
-    std::string maps_data_str((std::istreambuf_iterator<char>(maps_file)), std::istreambuf_iterator<char>());
-    StringRef maps_data(maps_data_str.c_str());
-
-    while (!maps_data.empty())
+    bool found = false;
+    file_spec.Clear();
+    ProcFileReader::ProcessLineByLine(GetID(), "maps",
+        [&] (const std::string &line)
         {
-        StringRef maps_row;
-        std::tie(maps_row, maps_data) = maps_data.split('\n');
-
-        SmallVector<StringRef, 16> maps_columns;
-        maps_row.split(maps_columns, StringRef(" "), -1, false);
+            SmallVector<StringRef, 16> columns;
+            StringRef(line).split(columns, " ", -1, false);
+            if (columns.size() < 6)
+                return true; // continue searching
+
+            FileSpec this_file_spec(columns[5].str().c_str(), false);
+            if (this_file_spec.GetFilename() != module_file_spec.GetFilename())
+                return true; // continue searching
 
-        if (maps_columns.size() >= 6)
-        {
-            file_spec.SetFile(maps_columns[5].str().c_str(), false);
-            if (file_spec.GetFilename() == module_file_spec.GetFilename())
-                return Error();
-        }
-    }
+            file_spec = this_file_spec;
+            found = true;
+            return false; // we are done
+        });
 
-    file_spec.Clear();
+    if (! found)
         return Error("Module file (%s) not found in /proc/%" PRIu64 "/maps file!",
-                 module_file_spec.GetFilename().AsCString(), GetID());
+
+    return Error();
 }
 
 Error
 NativeProcessLinux::GetFileLoadAddress(const llvm::StringRef& file_name, lldb::addr_t& load_addr)
 {
     load_addr = LLDB_INVALID_ADDRESS;
     Error error = ProcFileReader::ProcessLineByLine (GetID (), "maps",
         [&] (const std::string &line) -> bool