Log: Fix out-of-order log messages during HTML build [#646]

100_core/src/gplx/Gfo_usr_dlg__log_base.java

@@ -16,6 +16,7 @@ Apache License: https://github.com/gnosygnu/xowa/blob/master/LICENSE-APACHE2.txt
 package gplx;
 import gplx.core.strings.*; import gplx.core.consoles.*; import gplx.core.brys.fmtrs.*;
 public class Gfo_usr_dlg__log_base implements Gfo_usr_dlg__log {
+	private final    Object thread_lock = new Object();
 	private int archive_dirs_max = 8;
 	private Io_url log_dir, err_fil;
 	private final    Ordered_hash queued_list = Ordered_hash_.New();
@@ -85,8 +86,11 @@ public class Gfo_usr_dlg__log_base implements Gfo_usr_dlg__log {
 		} 
 		catch (Exception e) {Err_.Noop(e);}			// java.lang.StringBuilder can throw exceptions in some situations when called on a different thread; ignore errors
 	}	private String_bldr sb = String_bldr_.new_thread();	// NOTE: use java.lang.StringBuffer to try to avoid random exceptions when called on a different thread
-	private String Bld_msg(String s) {return sb.Add(Datetime_now.Get_force().XtoUtc().XtoStr_fmt_yyyyMMdd_HHmmss_fff()).Add(" ").Add(s).Add_char_nl().To_str_and_clear();}
+	private String Bld_msg(String s) {
+		return sb.Add(Datetime_now.Get_force().XtoUtc().XtoStr_fmt_yyyyMMdd_HHmmss_fff()).Add(" ").Add(s).Add_char_nl().To_str_and_clear();
+	}
 	private void Log_msg(Io_url url, String txt) {
+		synchronized (thread_lock) { // THREAD:synchronized neded b/c queued_list can be accessible by multiple threads; ISSUE#:646; DATE:2020-01-09
 		if (queue_enabled) {
 			String url_raw = url == null ? "mem" : url.Raw();
 			Usr_log_fil fil = (Usr_log_fil)queued_list.Get_by(url_raw);
@@ -100,6 +104,7 @@ public class Gfo_usr_dlg__log_base implements Gfo_usr_dlg__log {
 			if (enabled)
 				Io_mgr.Instance.AppendFilStr(url, txt);
 		}
+		}
 	}
 	public Object Invk(GfsCtx ctx, int ikey, String k, GfoMsg m) {
 		if		(ctx.Match(k, "enabled_"))				enabled = m.ReadYn("v");