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Mitigated possible race condition during app startup

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This commit is contained in:
Itay Grudev 2020-09-09 00:28:02 +01:00
parent 81052d9a61
commit e4282f2476
4 changed files with 101 additions and 51 deletions
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76
singleapplication.cpp
View File

@ -74,17 +74,28 @@ SingleApplication::SingleApplication( int &argc, char *argv[], bool allowSeconda
// Create a shared memory block
if( d->memory->create( sizeof( InstancesInfo ) )){
// Initialize the shared memory block
d->memory->lock();
d->initializeMemoryBlock();
} else {
// Attempt to attach to the memory segment
if( ! d->memory->attach() ){
qCritical() << "SingleApplication: Unable to attach to shared memory block.";
qCritical() << d->memory->errorString();
delete d;
::exit( EXIT_FAILURE );
if( ! d->memory->lock() ){
qCritical() << "SingleApplication: Unable to lock memory block after create.";
abortSafely();
}
d->initializeMemoryBlock();
qDebug() << "SingleApplication: Created and initialized new memory block.";
} else {
if( d->memory->error() == QSharedMemory::AlreadyExists ){
// Attempt to attach to the memory segment
if( ! d->memory->attach() ){
qCritical() << "SingleApplication: Unable to attach to shared memory block.";
abortSafely();
}
if( ! d->memory->lock() ){
qCritical() << "SingleApplication: Unable to lock memory block after attach.";
abortSafely();
}
qDebug() << "SingleApplication: Attached to new memory block.";
} else {
qCritical() << "SingleApplication: Unable create block.";
abortSafely();
}
d->memory->lock();
}
auto *inst = static_cast<InstancesInfo*>( d->memory->data() );
@ -93,9 +104,13 @@ SingleApplication::SingleApplication( int &argc, char *argv[], bool allowSeconda
// Make sure the shared memory block is initialised and in consistent state
while( true ){
qDebug() << "SingleApplication: Verifying block checksum.";
// If the shared memory block's checksum is valid continue
if( d->blockChecksum() == inst->checksum ) break;
qDebug() << "SingleApplication: Invalid block checksum. Waiting.";
// If more than 5s have elapsed, assume the primary instance crashed and
// assume it's position
if( time.elapsed() > 5000 ){
@ -106,36 +121,48 @@ SingleApplication::SingleApplication( int &argc, char *argv[], bool allowSeconda
// Otherwise wait for a random period and try again. The random sleep here
// limits the probability of a collision between two racing apps and
// allows the app to initialise faster
d->memory->unlock();
if( ! d->memory->unlock() ){
qDebug() << "SingleApplication: Unable to unlock memory for random wait.";
qDebug() << d->memory->errorString();
}
#if QT_VERSION >= QT_VERSION_CHECK( 5, 10, 0 )
QThread::sleep( QRandomGenerator::global()->bounded( 8u, 18u ));
#else
qsrand( QDateTime::currentMSecsSinceEpoch() % std::numeric_limits<uint>::max() );
QThread::sleep( 8 + static_cast <unsigned long>( static_cast <float>( qrand() ) / RAND_MAX * 10 ));
#endif
d->memory->lock();
if( ! d->memory->lock() ){
qCritical() << "SingleApplication: Unable to lock memory after random wait.";
abortSafely();
}
}
if( inst->primary == false ){
d->startPrimary();
d->memory->unlock();
if( ! d->memory->unlock() ){
qDebug() << "SingleApplication: Unable to unlock memory after primary start.";
qDebug() << d->memory->errorString();
}
return;
}
// Check if another instance can be started
if( allowSecondary ){
inst->secondary += 1;
inst->checksum = d->blockChecksum();
d->instanceNumber = inst->secondary;
d->startSecondary();
if( d->options & Mode::SecondaryNotification ){
d->connectToPrimary( timeout, SingleApplicationPrivate::SecondaryInstance );
}
d->memory->unlock();
if( ! d->memory->unlock() ){
qDebug() << "SingleApplication: Unable to unlock memory after secondary start.";
qDebug() << d->memory->errorString();
}
return;
}
d->memory->unlock();
if( ! d->memory->unlock() ){
qDebug() << "SingleApplication: Unable to unlock memory at end of execution.";
qDebug() << d->memory->errorString();
}
d->connectToPrimary( timeout, SingleApplicationPrivate::NewInstance );
@ -235,3 +262,16 @@ bool SingleApplication::sendMessage( const QByteArray &message, int timeout )
d->socket->flush();
return dataWritten;
}
/**
* Cleans up the shared memory block and exits with a failure.
* This function halts program execution.
*/
void SingleApplication::abortSafely()
{
Q_D( SingleApplication );
qCritical() << d->memory->errorString();
delete d;
::exit( EXIT_FAILURE );
}

1
singleapplication.h
View File

@ -140,6 +140,7 @@ Q_SIGNALS:
private:
SingleApplicationPrivate *d_ptr;
Q_DECLARE_PRIVATE(SingleApplication)
void abortSafely();
};
Q_DECLARE_OPERATORS_FOR_FLAGS(SingleApplication::Options)

73
singleapplication_p.cpp
View File

@ -64,15 +64,15 @@ SingleApplicationPrivate::SingleApplicationPrivate( SingleApplication *q_ptr )
SingleApplicationPrivate::~SingleApplicationPrivate()
{
if( socket != nullptr ) {
if( socket != nullptr ){
socket->close();
delete socket;
}
if( memory != nullptr ) {
if( memory != nullptr ){
memory->lock();
auto *inst = static_cast<InstancesInfo*>(memory->data());
if( server != nullptr ) {
if( server != nullptr ){
server->close();
delete server;
inst->primary = false;
@ -106,7 +106,7 @@ QString SingleApplicationPrivate::getUsername()
struct passwd *pw = getpwuid( uid );
if( pw )
username = QString::fromLocal8Bit( pw->pw_name );
if ( username.isEmpty() ) {
if ( username.isEmpty() ){
#if QT_VERSION < QT_VERSION_CHECK(5, 10, 0)
username = QString::fromLocal8Bit( qgetenv( "USER" ) );
#else
@ -125,11 +125,11 @@ void SingleApplicationPrivate::genBlockServerName()
appData.addData( SingleApplication::app_t::organizationName().toUtf8() );
appData.addData( SingleApplication::app_t::organizationDomain().toUtf8() );
if( ! (options & SingleApplication::Mode::ExcludeAppVersion) ) {
if( ! (options & SingleApplication::Mode::ExcludeAppVersion) ){
appData.addData( SingleApplication::app_t::applicationVersion().toUtf8() );
}
if( ! (options & SingleApplication::Mode::ExcludeAppPath) ) {
if( ! (options & SingleApplication::Mode::ExcludeAppPath) ){
#ifdef Q_OS_WIN
appData.addData( SingleApplication::app_t::applicationFilePath().toLower().toUtf8() );
#else
@ -138,7 +138,7 @@ void SingleApplicationPrivate::genBlockServerName()
}
// User level block requires a user specific data in the hash
if( options & SingleApplication::Mode::User ) {
if( options & SingleApplication::Mode::User ){
appData.addData( getUsername().toUtf8() );
}
@ -161,6 +161,17 @@ void SingleApplicationPrivate::startPrimary()
{
Q_Q(SingleApplication);
// Reset the number of connections
auto *inst = static_cast <InstancesInfo*>( memory->data() );
inst->primary = true;
inst->primaryPid = q->applicationPid();
qstrncpy( inst->primaryUser, getUsername().toUtf8().data(), sizeof(inst->primaryUser) );
inst->checksum = blockChecksum();
instanceNumber = 0;
qDebug() << "SingleApplication: Started as a primary instance.";
// Successful creation means that no main process exists
// So we start a QLocalServer to listen for connections
QLocalServer::removeServer( blockServerName );
@ -168,7 +179,7 @@ void SingleApplicationPrivate::startPrimary()
// Restrict access to the socket according to the
// SingleApplication::Mode::User flag on User level or no restrictions
if( options & SingleApplication::Mode::User ) {
if( options & SingleApplication::Mode::User ){
server->setSocketOptions( QLocalServer::UserAccessOption );
} else {
server->setSocketOptions( QLocalServer::WorldAccessOption );
@ -181,27 +192,24 @@ void SingleApplicationPrivate::startPrimary()
this,
&SingleApplicationPrivate::slotConnectionEstablished
);
// Reset the number of connections
auto *inst = static_cast <InstancesInfo*>( memory->data() );
inst->primary = true;
inst->primaryPid = q->applicationPid();
qstrncpy( inst->primaryUser, getUsername().toUtf8().data(), sizeof(inst->primaryUser) );
inst->checksum = blockChecksum();
instanceNumber = 0;
}
void SingleApplicationPrivate::startSecondary()
{
auto *inst = static_cast <InstancesInfo*>( memory->data() );
inst->secondary += 1;
inst->checksum = blockChecksum();
instanceNumber = inst->secondary;
qDebug() << "SingleApplication: Started as a secondary instance.";
}
void SingleApplicationPrivate::connectToPrimary( int msecs, ConnectionType connectionType )
{
// Connect to the Local Server of the Primary Instance if not already
// connected.
if( socket == nullptr ) {
if( socket == nullptr ){
socket = new QLocalSocket();
}
@ -211,17 +219,17 @@ void SingleApplicationPrivate::connectToPrimary( int msecs, ConnectionType conne
// If not connect
if( socket->state() == QLocalSocket::UnconnectedState ||
socket->state() == QLocalSocket::ClosingState ) {
socket->state() == QLocalSocket::ClosingState ){
socket->connectToServer( blockServerName );
}
// Wait for being connected
if( socket->state() == QLocalSocket::ConnectingState ) {
if( socket->state() == QLocalSocket::ConnectingState ){
socket->waitForConnected( msecs );
}
// Initialisation message according to the SingleApplication protocol
if( socket->state() == QLocalSocket::ConnectedState ) {
if( socket->state() == QLocalSocket::ConnectedState ){
// Notify the parent that a new instance had been started;
QByteArray initMsg;
QDataStream writeStream(&initMsg, QIODevice::WriteOnly);
@ -293,7 +301,7 @@ void SingleApplicationPrivate::slotConnectionEstablished()
connectionMap.insert(nextConnSocket, ConnectionInfo());
QObject::connect(nextConnSocket, &QLocalSocket::aboutToClose,
[nextConnSocket, this]() {
[nextConnSocket, this](){
auto &info = connectionMap[nextConnSocket];
Q_EMIT this->slotClientConnectionClosed( nextConnSocket, info.instanceId );
}
@ -307,9 +315,9 @@ void SingleApplicationPrivate::slotConnectionEstablished()
);
QObject::connect(nextConnSocket, &QLocalSocket::readyRead,
[nextConnSocket, this]() {
[nextConnSocket, this](){
auto &info = connectionMap[nextConnSocket];
switch(info.stage) {
switch(info.stage){
case StageHeader:
readInitMessageHeader(nextConnSocket);
break;
@ -328,11 +336,11 @@ void SingleApplicationPrivate::slotConnectionEstablished()
void SingleApplicationPrivate::readInitMessageHeader( QLocalSocket *sock )
{
if (!connectionMap.contains( sock )) {
if (!connectionMap.contains( sock )){
return;
}
if( sock->bytesAvailable() < ( qint64 )sizeof( quint64 ) ) {
if( sock->bytesAvailable() < ( qint64 )sizeof( quint64 ) ){
return;
}
@ -349,7 +357,7 @@ void SingleApplicationPrivate::readInitMessageHeader( QLocalSocket *sock )
info.stage = StageBody;
info.msgLen = msgLen;
if ( sock->bytesAvailable() >= (qint64) msgLen ) {
if ( sock->bytesAvailable() >= (qint64) msgLen ){
readInitMessageBody( sock );
}
}
@ -358,12 +366,12 @@ void SingleApplicationPrivate::readInitMessageBody( QLocalSocket *sock )
{
Q_Q(SingleApplication);
if (!connectionMap.contains( sock )) {
if (!connectionMap.contains( sock )){
return;
}
ConnectionInfo &info = connectionMap[sock];
if( sock->bytesAvailable() < ( qint64 )info.msgLen ) {
if( sock->bytesAvailable() < ( qint64 )info.msgLen ){
return;
}
@ -399,7 +407,7 @@ void SingleApplicationPrivate::readInitMessageBody( QLocalSocket *sock )
QLatin1String(latin1Name) == blockServerName &&
msgChecksum == actualChecksum;
if( !isValid ) {
if( !isValid ){
sock->close();
return;
}
@ -411,10 +419,11 @@ void SingleApplicationPrivate::readInitMessageBody( QLocalSocket *sock )
( connectionType == SecondaryInstance &&
options & SingleApplication::Mode::SecondaryNotification ) )
{
qDebug() << "SingleApplication: instanceStarted()";
Q_EMIT q->instanceStarted();
}
if (sock->bytesAvailable() > 0) {
if (sock->bytesAvailable() > 0){
Q_EMIT this->slotDataAvailable( sock, instanceId );
}
}

2
singleapplication_p.h
View File

@ -41,8 +41,8 @@ struct InstancesInfo {
bool primary;
quint32 secondary;
qint64 primaryPid;
quint16 checksum;
char primaryUser[128];
quint16 checksum; // Must be the last field
};
struct ConnectionInfo {