push_message
Description:
Call this function to describe an operation being performed.
Call camel_operation_progress to report progress on the operation. Call camel_operation_pop_message when the
operation is complete.
This function only works if cancellable is a Operation cast as a
Cancellable. If cancellable is a plain
Cancellable or null, the function does nothing and
returns silently.
Parameters:
| format |
a standard printf format string |
| ... |
the parameters to insert into the format string |
| cancellable |
a Cancellable or null |