Current send thread could work while the sync mechanism has some problem:

  * has spuriously wakeup
  * number of channels_ready will *overflow* the number of real channels

The reason is:

  * if MULTIFD_FLAG_SYNC is set in the middle of send thread running, there
    is one more spurious wakeup
  * if MULTIFD_FLAG_SYNC is set when send thread is not running, there is one
    more channels_ready be triggered 

To solve this situation, one new mechanism is introduced to synchronize send
threads. The idea is simple, a new field *sync* is introduced to indicate a
synchronization is required.

Wei Yang (6):
  migration/multifd: move MultiFDSendParams handling into
    multifd_send_fill_packet()
  migration/multifd: notify channels_ready when send thread starts
  migration/multifd: use sync field to synchronize send threads
  migration/multifd: used must not be 0 for a pending job
  migration/multifd: use boolean for pending_job is enough
  migration/multifd: there is no spurious wakeup now

 migration/ram.c | 62 +++++++++++++++++++++++++++++++------------------
 1 file changed, 39 insertions(+), 23 deletions(-)

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2.19.1