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authorDavid Fries <David@Fries.net>2015-11-24 17:29:59 -0600
committerDavid Fries <david@fries.net>2015-12-11 17:59:52 +0000
commitb2c7c489ab40efb1f2f64aba5b90f5f4fb8d8536 (patch)
tree73a2f1eea66428c904c50dd99526e1a050581d0f /src/corelib/io
parent672f7dfdcd00d124cd0f973e04e3e2d6445d5483 (diff)
QLockFile: decide on locking strategy per path
It is filesystem dependent if flock and fcntl locks are independent or the same underlying lock (which causes getting the second lock to fail). A temporary file in /tmp might be on a local file system and pass while the lock file is placed on NFS and fail with: setNativeLocks failed: Resource temporarily unavailable Instead check for lock conflicts per path and cache the result. Change-Id: I39c59bb240cd99ef0a0ec271243770ffd5df8a7d Reviewed-by: David Faure <david.faure@kdab.com>
Diffstat (limited to 'src/corelib/io')
-rw-r--r--src/corelib/io/qlockfile_p.h2
-rw-r--r--src/corelib/io/qlockfile_unix.cpp42
2 files changed, 30 insertions, 14 deletions
diff --git a/src/corelib/io/qlockfile_p.h b/src/corelib/io/qlockfile_p.h
index 168062f467..48b642abd0 100644
--- a/src/corelib/io/qlockfile_p.h
+++ b/src/corelib/io/qlockfile_p.h
@@ -78,7 +78,7 @@ public:
static QString processNameByPid(qint64 pid);
#ifdef Q_OS_UNIX
- static int checkFcntlWorksAfterFlock();
+ static int checkFcntlWorksAfterFlock(const QString &fn);
#endif
QString fileName;
diff --git a/src/corelib/io/qlockfile_unix.cpp b/src/corelib/io/qlockfile_unix.cpp
index bd9f8a5988..667b108ba0 100644
--- a/src/corelib/io/qlockfile_unix.cpp
+++ b/src/corelib/io/qlockfile_unix.cpp
@@ -39,6 +39,10 @@
#include "QtCore/qfileinfo.h"
#include "QtCore/qdebug.h"
#include "QtCore/qdatetime.h"
+#include "QtCore/qfileinfo.h"
+#include "QtCore/qcache.h"
+#include "QtCore/qglobalstatic.h"
+#include "QtCore/qmutex.h"
#include "private/qcore_unix_p.h" // qt_safe_open
#include "private/qabstractfileengine_p.h"
@@ -89,10 +93,10 @@ static qint64 qt_write_loop(int fd, const char *data, qint64 len)
return pos;
}
-int QLockFilePrivate::checkFcntlWorksAfterFlock()
+int QLockFilePrivate::checkFcntlWorksAfterFlock(const QString &fn)
{
#ifndef QT_NO_TEMPORARYFILE
- QTemporaryFile file;
+ QTemporaryFile file(fn);
if (!file.open())
return 0;
const int fd = file.d_func()->engine()->handle();
@@ -114,24 +118,34 @@ int QLockFilePrivate::checkFcntlWorksAfterFlock()
#endif
}
-static QBasicAtomicInt fcntlOK = Q_BASIC_ATOMIC_INITIALIZER(-1);
+// Cache the result of checkFcntlWorksAfterFlock for each directory a lock
+// file is created in because in some filesystems, like NFS, both locks
+// are the same. This does not take into account a filesystem changing.
+// QCache is set to hold a maximum of 10 entries, this is to avoid unbounded
+// growth, this is caching directories of files and it is assumed a low number
+// will be sufficient.
+typedef QCache<QString, bool> CacheType;
+Q_GLOBAL_STATIC_WITH_ARGS(CacheType, fcntlOK, (10));
+static QBasicMutex fcntlLock;
/*!
\internal
Checks that the OS isn't using POSIX locks to emulate flock().
OS X is one of those.
*/
-static bool fcntlWorksAfterFlock()
+static bool fcntlWorksAfterFlock(const QString &fn)
{
- int value = fcntlOK.load();
- if (Q_UNLIKELY(value == -1)) {
- value = QLockFilePrivate::checkFcntlWorksAfterFlock();
- fcntlOK.store(value);
+ QMutexLocker lock(&fcntlLock);
+ bool *worksPtr = fcntlOK->object(fn);
+ if (!worksPtr) {
+ worksPtr = new bool(QLockFilePrivate::checkFcntlWorksAfterFlock(fn));
+ fcntlOK->insert(fn, worksPtr);
}
- return value == 1;
+
+ return *worksPtr;
}
-static bool setNativeLocks(int fd)
+static bool setNativeLocks(const QString &fileName, int fd)
{
#if defined(LOCK_EX) && defined(LOCK_NB)
if (flock(fd, LOCK_EX | LOCK_NB) == -1) // other threads, and other processes on a local fs
@@ -143,8 +157,10 @@ static bool setNativeLocks(int fd)
flockData.l_start = 0;
flockData.l_len = 0; // 0 = entire file
flockData.l_pid = getpid();
- if (fcntlWorksAfterFlock() && fcntl(fd, F_SETLK, &flockData) == -1) // for networked filesystems
+ if (fcntlWorksAfterFlock(QDir::cleanPath(QFileInfo(fileName).absolutePath()) + QString('/'))
+ && fcntl(fd, F_SETLK, &flockData) == -1) { // for networked filesystems
return false;
+ }
return true;
}
@@ -171,7 +187,7 @@ QLockFile::LockError QLockFilePrivate::tryLock_sys()
}
}
// Ensure nobody else can delete the file while we have it
- if (!setNativeLocks(fd)) {
+ if (!setNativeLocks(fileName, fd)) {
const int errnoSaved = errno;
qWarning() << "setNativeLocks failed:" << qt_error_string(errnoSaved);
}
@@ -195,7 +211,7 @@ bool QLockFilePrivate::removeStaleLock()
const int fd = qt_safe_open(lockFileName.constData(), O_WRONLY, 0644);
if (fd < 0) // gone already?
return false;
- bool success = setNativeLocks(fd) && (::unlink(lockFileName) == 0);
+ bool success = setNativeLocks(fileName, fd) && (::unlink(lockFileName) == 0);
close(fd);
return success;
}