Comment 18 for bug 56369

SVN commit 513455 by osterfeld:

Lock archive to avoid metakit archive corruption due to multiple write access.
Usually Akregator being a KUniqueApplication avoids multiple Akregator instances accessing the archive, but there seem to
be some cases where KUniqueApp is not safe enough (right after update, multiple KDE sessions, when using --nofork option).
So we lock the archive like KMail does: if locking fails, show an error message to the user, giving him the possibility to
either continue without archive, or to force access.
As this is a severe bug (multiple write access can corrupt archives, which can make Akregator crash at startup), I think
making use of the message unfreeze is justified.
CCBUG: 116482
CCMAIL:<email address hidden>
CCMAIL:<email address hidden>

 M +133 -1 akregator_part.cpp
 M +2 -0 akregator_part.h
 A kcursorsaver.h [License: no copyright]

--- branches/KDE/3.5/kdepim/akregator/src/akregator_part.cpp #513454:513455
@@ -56,6 +56,13 @@
 #include <qwidgetlist.h>
 #include <private/qucomextra_p.h>

+#include <cerrno>
+#include <sys/types.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
 #include "aboutdata.h"
 #include "actionmanagerimpl.h"
 #include "akregator_part.h"
@@ -68,6 +75,7 @@
 #include "frame.h"
 #include "article.h"
 #include "kernel.h"
+#include "kcursorsaver.h"
 #include "notificationmanager.h"
 #include "pageviewer.h"
 #include "plugin.h"
@@ -135,8 +143,21 @@

     m_storage = 0;
     Backend::StorageFactory* factory = Backend::StorageFactoryRegistry::self()->getFactory(Settings::archiveBackend());
+
     if (factory != 0)
- m_storage = factory->createStorage(QStringList());
+ {
+
+ if (Settings::archiveBackend() == "metakit")
+ {
+ if (tryToLock(factory->name()))
+ m_storage = factory->createStorage(QStringList());
+ else
+ m_storage = dummyFactory->createStorage(QStringList());
+ }
+ else
+ m_storage = factory->createStorage(QStringList());
+ }
+

     if (!m_storage) // Houston, we have a problem
     {
@@ -877,6 +898,117 @@
     return false;
 }

+static QString getMyHostName()
+{
+ char hostNameC[256];
+ // null terminate this C string
+ hostNameC[255] = 0;
+ // set the string to 0 length if gethostname fails
+ if(gethostname(hostNameC, 255))
+ hostNameC[0] = 0;
+ return QString::fromLocal8Bit(hostNameC);
+}

+// taken from KMail
+bool Part::tryToLock(const QString& backendName)
+{
+// Check and create a lock file to prevent concurrent access to metakit archive
+ QString appName = kapp->instanceName();
+ if ( appName.isEmpty() )
+ appName = "akregator";
+
+ QString programName;
+ const KAboutData *about = kapp->aboutData();
+ if ( about )
+ programName = about->programName();
+ if ( programName.isEmpty() )
+ programName = i18n("Akregator");
+
+ QString lockLocation = locateLocal("data", "akregator/lock");
+ KSimpleConfig config(lockLocation);
+ int oldPid = config.readNumEntry("pid", -1);
+ const QString oldHostName = config.readEntry("hostname");
+ const QString oldAppName = config.readEntry( "appName", appName );
+ const QString oldProgramName = config.readEntry( "programName", programName );
+ const QString hostName = getMyHostName();
+ bool first_instance = false;
+ if ( oldPid == -1 )
+ first_instance = true;
+ // check if the lock file is stale by trying to see if
+ // the other pid is currently running.
+ // Not 100% correct but better safe than sorry
+ else if (hostName == oldHostName && oldPid != getpid()) {
+ if ( kill(oldPid, 0) == -1 )
+ first_instance = ( errno == ESRCH );
+ }
+
+ if ( !first_instance )
+ {
+ QString msg;
+ if ( oldHostName == hostName )
+ {
+ // this can only happen if the user is running this application on
+ // different displays on the same machine. All other cases will be
+ // taken care of by KUniqueApplication()
+ if ( oldAppName == appName )
+ msg = i18n("<qt>%1 already seems to be running on another display on "
+ "this machine. <b>Running %2 more than once is not supported "
+ "by the %3 backend and "
+ "can cause the loss of archived articles and crashes at startup.</b> "
+ "You should disable the archive for now "
+ "unless you are sure that %2 is not already running.</qt>")
+ .arg( programName, programName, backendName );
+ // QString::arg( st ) only replaces the first occurrence of %1
+ // with st while QString::arg( s1, s2 ) replacess all occurrences
+ // of %1 with s1 and all occurrences of %2 with s2. So don't
+ // even think about changing the above to .arg( programName ).
+ else
+ msg = i18n("<qt>%1 seems to be running on another display on this "
+ "machine. <b>Running %1 and %2 at the same "
+ "time is not supported by the %3 backend and can cause "
+ "the loss of archived articles and crashes at startup.</b> "
+ "You should disable the archive for now "
+ "unless you are sure that %2 is not already running.</qt>")
+ .arg( oldProgramName, programName, backendName );
+ }
+ else
+ {
+ if ( oldAppName == appName )
+ msg = i18n("<qt>%1 already seems to be running on %2. <b>Running %1 more "
+ "than once is not supported by the %3 backend and can cause "
+ "the loss of archived articles and crashes at startup.</b> "
+ "You should disable the archive for now "
+ "unless you are sure that it is "
+ "not already running on %2.</qt>")
+ .arg( programName, oldHostName, backendName );
+ else
+ msg = i18n("<qt>%1 seems to be running on %3. <b>Running %1 and %2 at the "
+ "same time is not supported by the %4 backend and can cause "
+ "the loss of archived articles and crashes at startup.</b> "
+ "You should disable the archive for now "
+ "unless you are sure that %1 is "
+ "not running on %3.</qt>")
+ .arg( oldProgramName, programName, oldHostName, backendName );
+ }
+
+ KCursorSaver idle( KBusyPtr::idle() );
+ if ( KMessageBox::No ==
+ KMessageBox::warningYesNo( 0, msg, QString::null,
+ i18n("Force Access"),
+ i18n("Disable Archive")) )
+ {
+ return false;
+ }
+ }
+
+ config.writeEntry("pid", getpid());
+ config.writeEntry("hostname", hostName);
+ config.writeEntry( "appName", appName );
+ config.writeEntry( "programName", programName );
+ config.sync();
+ return true;
+}
+
+
 } // namespace Akregator
 #include "akregator_part.moc"
--- branches/KDE/3.5/kdepim/akregator/src/akregator_part.h #513454:513455
@@ -195,6 +195,8 @@
             /** creates an OPML file containing the initial feeds (KDE feeds) */
             static QDomDocument createDefaultFeedList();

+ bool tryToLock(const QString& backendName);
+
          private: // attributes

             class ApplyFiltersInterceptor;