Prevent using temporary codec-for-locale UTF8 replacement

Utf8CodecForLocaleReplacer's temporary codec-for-locale replacements
cause race conditions in unrelated code that calls
QTextCodec::codecForLocale(). Implement and use a wrapper function that
calls QTextCodec::codecForLocale() while holding
Utf8CodecForLocaleReplacer's mutex lock to fix it.

f0b66f7507 and this commit fix #1587.

Combine several chained QString::arg() calls into one in
EpwingBook::setErrorString(). A single call is more efficient and
prevents unintended replacement inside previous argument substitutions.

epwing_book.cc

@@ -420,10 +420,10 @@ EpwingBook::~EpwingBook()
 
 void EpwingBook::setErrorString( QString const & func, EB_Error_Code code )
 {
+  QTextCodec * const localeCodec = gdCodecForLocale();
   error_string = QString( "EB \"%1\" function error: %2 (%3)" )
-                 .arg( func )
+                 .arg( func, localeCodec->toUnicode( eb_error_string( code ) ),
-                 .arg( QTextCodec::codecForLocale()->toUnicode( eb_error_string( code ) ) )
+                       localeCodec->toUnicode( eb_error_message( code ) ) );
-                 .arg( QTextCodec::codecForLocale()->toUnicode( eb_error_message( code ) ) );
 
   if( currentPosition.page != 0 )
     error_string += QString( " on page %1, offset %2" ).arg( QString::number( currentPosition.page ) )

gddebug.cc

@@ -2,6 +2,7 @@
  * Part of GoldenDict. Licensed under GPLv3 or later, see the LICENSE file */
 
 #include <QMutex>
+#include <QMutexLocker>
 #include <QTextCodec>
 #include <QString>
 #include "gddebug.hh"
@@ -13,6 +14,17 @@ namespace {
 class Utf8CodecForLocaleReplacer
 {
 public:
+  static QTextCodec * originalCodecForLocale()
+  {
+    if( !shouldReplaceCodecForLocale() )
+      return QTextCodec::codecForLocale();
+    // codecForLocaleMutex is locked while the UTF8 codec replaces the original codec.
+    // Thus calling QTextCodec::codecForLocale() while holding a lock is guaranteed to
+    // return the original codec, not its temporary UTF8 replacement.
+    QMutexLocker _( &codecForLocaleMutex );
+    return QTextCodec::codecForLocale();
+  }
+
   Utf8CodecForLocaleReplacer():
     replaceCodecForLocale( shouldReplaceCodecForLocale() ), localeCodec( 0 )
   {
@@ -68,3 +80,8 @@ void gdDebug(const char *msg, ...)
   }
   va_end(ap);
 }
+
+QTextCodec * gdCodecForLocale()
+{
+  return Utf8CodecForLocaleReplacer::originalCodecForLocale();
+}

gddebug.hh

@@ -3,6 +3,8 @@
 
 #include <QFile>
 
+class QTextCodec;
+
 #ifdef NO_CONSOLE
   #define GD_DPRINTF(...) do {} while( 0 )
   #define GD_FDPRINTF(...) do {} while( 0 )
@@ -27,6 +29,8 @@ void gdDebug(const char *, ...)
 #endif
 ;
 
+QTextCodec * gdCodecForLocale();
+
 extern QFile * logFilePtr;
 
 #endif // __GDDEBUG_HH_INCLUDED__

indexedzip.cc

@@ -133,7 +133,7 @@ bool IndexedZip::indexFile( BtreeIndexing::IndexedWords &zipFileNames, quint32 *
     // File seems to be a valid zip file
 
 
-    QTextCodec * localeCodec = QTextCodec::codecForLocale();
+    QTextCodec * const localeCodec = gdCodecForLocale();
 
     ZipFile::CentralDirEntry entry;