[LyX/2.1.x] Make Formats::isZippedFile() threadsafe

[Georg Baum]

commit 8fe58b90c2a1bcf2fba36d417c657935c28c5b6f
Author: Georg Baum <b...@lyx.org>
Date:   Mon Jul 7 21:34:54 2014 +0200

    Make Formats::isZippedFile() threadsafe
    
    In this case I use a mutex, so the zip status of files is shared between
    threads. This is possible because a deadlock can't happen, and it should 
give
    better performance.

diff --git a/src/Format.cpp b/src/Format.cpp
index 2bc7ac5..93383ac 100644
--- a/src/Format.cpp
+++ b/src/Format.cpp
@@ -22,6 +22,7 @@
 #include "support/filetools.h"
 #include "support/gettext.h"
 #include "support/lstrings.h"
+#include "support/mutex.h"
 #include "support/os.h"
 #include "support/PathChanger.h"
 #include "support/Systemcall.h"
@@ -479,11 +480,13 @@ struct ZippedInfo {
 
 /// Mapping absolute pathnames of files to their ZippedInfo metadata.
 static std::map<std::string, ZippedInfo> zipped_;
+static Mutex zipped_mutex;
 
 
 bool Formats::isZippedFile(support::FileName const & filename) const {
        string const & fname = filename.absFileName();
        time_t timestamp = filename.lastModified();
+       Mutex::Locker lock(&zipped_mutex);
        map<string, ZippedInfo>::iterator it = zipped_.find(fname);
        if (it != zipped_.end() && it->second.timestamp == timestamp)
                return it->second.zipped;