implement POSIX IPC based QSystemSemaphore and QSharedMemory backends

Merge-request: 1259
Reviewed-by: Harald Fernengel <harald.fernengel@nokia.com>

1 files changed, 124 insertions, 0 deletions

diff --git a/src/corelib/kernel/qsystemsemaphore_unix.cpp b/src/corelib/kernel/qsystemsemaphore_unix.cpp
index 704afaf1e4..ebf7d6f1ab 100644
--- a/src/corelib/kernel/qsystemsemaphore_unix.cpp
+++ b/src/corelib/kernel/qsystemsemaphore_unix.cpp
@@ -50,7 +50,9 @@
 
 #include <sys/types.h>
 #include <sys/ipc.h>
+#ifndef QT_POSIX_IPC
 #include <sys/sem.h>
+#endif
 #include <fcntl.h>
 #include <errno.h>
 
@@ -67,7 +69,11 @@
 QT_BEGIN_NAMESPACE
 
 QSystemSemaphorePrivate::QSystemSemaphorePrivate() :
+#ifndef QT_POSIX_IPC
     unix_key(-1), semaphore(-1), createdFile(false),
+#else
+    semaphore(SEM_FAILED),
+#endif
     createdSemaphore(false), error(QSystemSemaphore::NoError)
 {
 }
@@ -90,10 +96,18 @@ void QSystemSemaphorePrivate::setErrorString(const QString &function)
         error = QSystemSemaphore::NotFound;
         break;
     case ERANGE:
+    case ENOMEM:
     case ENOSPC:
+    case EMFILE:
+    case ENFILE:
+    case EOVERFLOW:
         errorString = QCoreApplication::translate("QSystemSemaphore", "%1: out of resources").arg(function);
         error = QSystemSemaphore::OutOfResources;
         break;
+    case ENAMETOOLONG:
+        errorString = QCoreApplication::translate("QSystemSemaphore", "%1: name error").arg(function);
+        error = QSystemSemaphore::KeyError;
+        break;
     default:
         errorString = QCoreApplication::translate("QSystemSemaphore", "%1: unknown error %2").arg(function).arg(errno);
         error = QSystemSemaphore::UnknownError;
@@ -109,6 +123,7 @@ void QSystemSemaphorePrivate::setErrorString(const QString &function)
 
     Initialise the semaphore
 */
+#ifndef QT_POSIX_IPC
 key_t QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode mode)
 {
     if (-1 != unix_key)
@@ -170,6 +185,54 @@ key_t QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode mode)
 
     return unix_key;
 }
+#else
+bool QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode mode)
+{
+    if (semaphore != SEM_FAILED)
+        return true;  // we already have a semaphore
+
+    if (fileName.isEmpty()) {
+        errorString = QCoreApplication::tr("%1: key is empty", "QSystemSemaphore").arg(QLatin1String("QSystemSemaphore::handle"));
+        error = QSystemSemaphore::KeyError;
+        return false;
+    }
+
+    QByteArray semName = QFile::encodeName(fileName);
+
+    // Always try with O_EXCL so we know whether we created the semaphore.
+    int oflag = O_CREAT | O_EXCL;
+    for (int tryNum = 0, maxTries = 1; tryNum < maxTries; ++tryNum) {
+        do {
+            semaphore = sem_open(semName.constData(), oflag, 0666, initialValue);
+        } while (semaphore == SEM_FAILED && errno == EINTR);
+        if (semaphore == SEM_FAILED && errno == EEXIST) {
+            if (mode == QSystemSemaphore::Create) {
+                if (sem_unlink(semName.constData()) == -1 && errno != ENOENT) {
+                    setErrorString(QLatin1String("QSystemSemaphore::handle (sem_unlink)"));
+                    return false;
+                }
+                // Race condition: the semaphore might be recreated before
+                // we call sem_open again, so we'll retry several times.
+                maxTries = 3;
+            } else {
+                // Race condition: if it no longer exists at the next sem_open
+                // call, we won't realise we created it, so we'll leak it later.
+                oflag &= ~O_EXCL;
+                maxTries = 2;
+            }
+        } else {
+            break;
+        }
+    }
+    if (semaphore == SEM_FAILED) {
+        setErrorString(QLatin1String("QSystemSemaphore::handle"));
+        return false;
+    }
+
+    createdSemaphore = (oflag & O_EXCL) != 0;
+    return true;
+}
+#endif // QT_POSIX_IPC
 
 /*!
     \internal
@@ -178,6 +241,7 @@ key_t QSystemSemaphorePrivate::handle(QSystemSemaphore::AccessMode mode)
 */
 void QSystemSemaphorePrivate::cleanHandle()
 {
+#ifndef QT_POSIX_IPC
     unix_key = -1;
 
     // remove the file if we made it
@@ -198,6 +262,27 @@ void QSystemSemaphorePrivate::cleanHandle()
         }
         createdSemaphore = false;
     }
+#else
+    if (semaphore != SEM_FAILED) {
+        if (sem_close(semaphore) == -1) {
+            setErrorString(QLatin1String("QSystemSemaphore::cleanHandle (sem_close)"));
+#ifdef QSYSTEMSEMAPHORE_DEBUG
+            qDebug() << QLatin1String("QSystemSemaphore::cleanHandle sem_close failed.");
+#endif
+        }
+        semaphore = SEM_FAILED;
+    }
+
+    if (createdSemaphore) {
+        if (sem_unlink(QFile::encodeName(fileName).constData()) == -1 && errno != ENOENT) {
+            setErrorString(QLatin1String("QSystemSemaphore::cleanHandle (sem_unlink)"));
+#ifdef QSYSTEMSEMAPHORE_DEBUG
+            qDebug() << QLatin1String("QSystemSemaphore::cleanHandle sem_unlink failed.");
+#endif
+        }
+        createdSemaphore = false;
+    }
+#endif // QT_POSIX_IPC
 }
 
 /*!
@@ -205,6 +290,7 @@ void QSystemSemaphorePrivate::cleanHandle()
 */
 bool QSystemSemaphorePrivate::modifySemaphore(int count)
 {
+#ifndef QT_POSIX_IPC
     if (-1 == handle())
         return false;
 
@@ -229,6 +315,44 @@ bool QSystemSemaphorePrivate::modifySemaphore(int count)
 #endif
         return false;
     }
+#else
+    if (!handle())
+        return false;
+
+    if (count > 0) {
+        int cnt = count;
+        do {
+            if (sem_post(semaphore) == -1) {
+                setErrorString(QLatin1String("QSystemSemaphore::modifySemaphore (sem_post)"));
+#ifdef QSYSTEMSEMAPHORE_DEBUG
+                qDebug() << QLatin1String("QSystemSemaphore::modify sem_post failed") << count << errno;
+#endif
+                // rollback changes to preserve the SysV semaphore behavior
+                for ( ; cnt < count; ++cnt) {
+                    register int res;
+                    EINTR_LOOP(res, sem_wait(semaphore));
+                }
+                return false;
+            }
+            --cnt;
+        } while (cnt > 0);
+    } else {
+        register int res;
+        EINTR_LOOP(res, sem_wait(semaphore));
+        if (res == -1) {
+            // If the semaphore was removed be nice and create it and then modifySemaphore again
+            if (errno == EINVAL || errno == EIDRM) {
+                semaphore = SEM_FAILED;
+                return modifySemaphore(count);
+            }
+            setErrorString(QLatin1String("QSystemSemaphore::modifySemaphore (sem_wait)"));
+#ifdef QSYSTEMSEMAPHORE_DEBUG
+            qDebug() << QLatin1String("QSystemSemaphore::modify sem_wait failed") << count << errno;
+#endif
+            return false;
+        }
+    }
+#endif // QT_POSIX_IPC
 
     return true;
 }