change: drop std::async, as it may involve new thread.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
update: a trying to add mutex.exp.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
move CanvasBackend out of Canvas.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
fix: several crush points. Notably, be careful on lambda slots connected to global objects.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
fix: wrong obj name.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
change: lock free again.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
change: use QQueue instead of QList to make queue.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
update: errcode message.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>
bump version;
fix: download url.

Signed-off-by: liuyanghejerry <liuyanghejerry@126.com>