Changeset 8055 in vbox for trunk/src/VBox/Main/xml/Settings.cpp

Timestamp:

Apr 16, 2008 5:50:24 PM (17 years ago)

Author:

vboxsync

Message:

Main/Settigs: Redone semi-faulty r29679: When reading from settings files, reopen them instead of reusing the existing hande to allow for concurrent multithreaded reads. Provided libxml2/libxslt reentrance (using global serialization) when parsing settings files.

File:

• trunk/src/VBox/Main/xml/Settings.cpp (modified) (8 diffs)

trunk/src/VBox/Main/xml/Settings.cpp

@@ -21 +21 @@
 #include <iprt/err.h>
 #include <iprt/file.h>
+#include <iprt/lock.h>
 
 #include <libxml/tree.h>
@@ -74 +75 @@
     {
         xmlExternalEntityLoader defaultEntityLoader;
+
+        /** Used to provide some thread safety missing in libxml2 (see e.g.
+         *  XmlTreeBackend::read()) */
+        RTLockMtx lock;
     }
     xml;
@@ -347 +352 @@
         : fileName (NULL), handle (NIL_RTFILE), opened (false) {}
 
-    Mode mode;
     char *fileName;
     RTFILE handle;
@@ -356 +360 @@
     : m (new Data())
 {
-    m->mode = aMode;
-
     m->fileName = RTStrDup (aFileName);
     if (m->fileName == NULL)
@@ -365 +367 @@
     switch (aMode)
     {
-        case Read:
+        case Mode_Read:
             flags = RTFILE_O_READ;
             break;
-        case Write:
+        case Mode_Write:
             flags = RTFILE_O_WRITE | RTFILE_O_CREATE;
             break;
-        case ReadWrite:
+        case Mode_ReadWrite:
             flags = RTFILE_O_READ | RTFILE_O_WRITE;
     }
@@ -382 +384 @@
 }
 
-File::File (Mode aMode, RTFILE aHandle, const char *aFileName /* = NULL */ )
+File::File (RTFILE aHandle, const char *aFileName /* = NULL */)
     : m (new Data())
 {
@@ -388 +390 @@
         throw EInvalidArg (RT_SRC_POS);
 
-    m->mode = aMode;
     m->handle = aHandle;
 
@@ -903 +904 @@
     m->trappedErr.reset();
 
-    /* Set up the external entity resolver. Note that we do it in a
-     * thread-unsafe fashion because this stuff is not thread-safe in libxml2.
-     * Making it thread-safe would require a) guarding this method with a
-     * mutex and b) requiring our API caller not to use libxml2 on some other
-     * thread (which is not practically possible). So, our API is not
-     * thread-safe for now (note that there are more thread-unsafe assumptions
-     * below like xsltGenericError which is also a libxslt limitation).*/
+    /* We use the global lock for the whole duration of this method to serialize
+     * access to thread-unsafe xmlGetExternalEntityLoader() and some other
+     * calls. It means that only one thread is able to parse an XML stream at a
+     * time but another choice would be to patch libxml2/libxslt which is
+     * unwanted now for several reasons. Search for "thread-safe" to find all
+     * unsafe cases. */
+    RTLock alock (gGlobal.xml.lock);
+
     xmlExternalEntityLoader oldEntityLoader = xmlGetExternalEntityLoader();
     sThat = this;