This method should not be public, but since it is used in a C-function and I don't know how I could declare a C-function to be a friend of a class...
The current implementation simply polls the sync manager data area of each slave and checks if wkc is incremented. Another solution is to configure FMMU's of each slave and query the slaves with one logical EtherCAT msg. This has the advantage of only using one message per slave, but it "sacrifices" an extra FMMU per slave, which might not always be possible. In that case, the master would---during the start_mbx_communication() call of slaves---configure an FMMU of the slave which listens to the written bit of sync manager 0.