#! /usr/bin/env mpenv
#
# This script monitors a user supplied list of EPICS PVs for callbacks.
#

import time
import Mp
import MpCa

if ( len(sys.argv) < 3 ):
	print ""
	print "Usage:  mpca_monitor pvname ..."
	print ""
	sys.exit(0)

#---------------------------------------------------------------------------

def pv_callback( callback, args ):

	pv = callback.pv

	print "'%s' = %s" % ( pv.pvname, str( pv.get_local() ) )

#---------------------------------------------------------------------------

pv_list       = []
callback_list = []

for arg in sys.argv[2:]:

	# Create a PV for this PV name

	pv = MpCa.PV( arg )

	print "Monitoring PV '%s'" % pv.pvname

	pv_list.append( pv )

	#
	# FIXME: Calling caget() should not be necessary, but it
	# helps to make the PV channel connect.
	#

	value = pv.caget()


if ( pv_list == [] ):
	print "No PV callbacks requested."
	sys.exit(0)

for pv in pv_list:
	callback = pv.add_callback( MpCa.DBE_VALUE, pv_callback, None )

	callback_list.append( callback )

	del callback

#
# Loop forever waiting for callbacks.
#
# NOTE: The presence of the call to time.sleep(0.001) in the loop
#       is _VERY_ important.  Calling time.sleep() causes the 
#       Python Global Interpreter Lock to be released which allows
#       the EPICS-triggered Python callback to run.  If the GIL is
#       not released on a regular interval by a call to something
#       like time.sleep(), then the EPICS-triggered Python callback
#       will often have to wait a very long time to acquire the GIL,
#       resulting in really bad performance for the EPICS callbacks.
#

while (True):

	MpCa.poll()

	if ( Mp.kbhit() ):
		break

	time.sleep(0.001)

print "Exiting..."