How I read mouse data In a non blocking way - mouse

Question

I'm implementing a fail safe handover procedure in ROS and I'm using python scripts to do so.
I'm using the optical sensor from a mouse to keep under control the acceleration of the object so I can detect when is falling. Everything seems to works fine but now I want to give give a limit to the monitoring procedure (let's say 1000 times) before declaring the handover succeded. The problem is that the function read that I use for the mouse get stucked, if no movement are detected the next iteration is not performed. How can I read from the device without encountering this issue?
Here is the code I'm using to read from the mouse:
def getMouseEvent():
buf = file.read(3)
x, y = struct.unpack( "bb", buf[1:] ) # <--- X and Y deltas.
return [x , y]
Here the loop I want to implement
release_grasp()
rospy.loginfo( "Force detected -- Release mode active")
# If the object is falling regrasp it.
detected= False
trials = 0
while (not(detected) and trials < 1000):
trials = trials + 1
rospy.loginfo ("Acc monitored for the" + str(trials) + "th time"
if fall_test():
cilindrical_grasp()
rospy.loginfo("Fall detected -- Object regrasped")
detected = True
rate.sleep()
The output I get blocks to a given iteration until the mouse does not detect some kind of movement.
UPDATE: Here is the full code
#!/usr/bin/env python2
import rospy
import numpy
import struct
from reflex_sf_msgs.msg import SFPose
from matteo.msg import force
from matteo.msg import acc
# Defining force treshold in each direction ( to be completed and tuned )
rospy.init_node('DetectionFail')
xt = 0.5
yt = xt
zt = 0.3
# For the future try to handle the initialization.
fx = None
fy = None
fz = None
ax = None
ay = None
rate = rospy.Rate(100) # <--- Rate Hz
#-----------------------------MOUSE-----------------------------------#
# Open the mouse device. To be sure if it is "mouse2" type in the terminal: cat /proc/bus/input/devices, look for the device whose name is "Logitech optical USB mouse" and get the name of the handler. If you need root permissions type: sudo chmod 777 /dev/input/(handler)
file = open ("/dev/input/mouse3" , "rb")
#Defining the function to read mouse deltas.
def getMouseEvent():
buf = file.read(3);
x,y = struct.unpack( "bb", buf[1:] ); # <--- X and Y deltas.
return [x , y]
#Defining the function to estimate the acceleraton.
def acc_comp():
vx_old = 0
vy_old = 0
vx_new = getMouseEvent()[0]
vy_new = getMouseEvent()[1]
x_acc = (vx_old - vx_new)*100
y_acc = (vy_old - vy_new)*100
vx_old = vx_new
vy_old = vy_new
return [x_acc , y_acc]
#---------------------------------------------------------------------#
#Defining function fall test
def fall_test():
if ( acc_comp()[1] >= 3000 or acc_comp()[1] <= -3000 ):
return True
else:
return False
#---------------------------------------------------------------------#
# Initialize hand publisher.
hand_pub = rospy.Publisher('/reflex_sf/command', SFPose, queue_size=1)
rospy.sleep(0.5)
#---------------------------------------------------------------------#
# Defining sferical grasp.
def cilindrical_grasp():
hand_pub.publish ( 2.5 , 2.5 , 2.5, 0)
#---------------------------------------------------------------------#
# Define release position.
def release_grasp():
hand_pub.publish ( 2, 2 , 2 , 0)
#---------------------------------------------------------------------#
# Define test for the force measure
def force_treshold ( fx, fy , fz):
if ( fx > xt and fy > yt or fz > zt):
return True
else:
return False
#---------------------------------------------------------------------#
# Callback function to save the datas obtained by the force sensor
def callback_force(msg):
global fx
global fy
global fz
fx = msg.fx
fy = msg.fy
fz = msg.fz
# Main loop.
def main():
#Apply the sferical grasp.
rospy.loginfo("Applying grasp")
cilindrical_grasp()
while not(rospy.is_shutdown()):
rospy.Subscriber("/Forces", force, callback_force )
if force_treshold ( fx , fy , fz ):
release_grasp()
rospy.loginfo( "Force detected -- Release mode active")
# If the object is falling regrasp it.
detected= False
trials = 0
while (not(detected) and trials < 1000):
trials = trials +1
if fall_test():
cilindrical_grasp()
rospy.loginfo("Fall detected -- Object regrasped")
detected = True
rate.sleep()
if rospy.is_shutdown() :
break
Yesterday I came out with this code:
#!/usr/bin/env python
import struct
import rospy
from matteo.msg import acc
import struct
import os
import time
i = 0
# Mouse read with a non blocking structure, the problem is that does not provide the same output as
# mouse_clean.py, probably there is a problem with the unpacking or the reading.
while i < 1000:
i += 1
try:
file = os.open("/dev/input/mouse0", os.O_RDONLY | os.O_NONBLOCK)
time.sleep(0.1)
buf = os.read(file , 3)
x,y = struct.unpack( "bb", buf[1:] ) # <--- X and Y deltas.
print ( "X:" +str ( x ) + "---" +"Y:" +str ( y ) )
except OSError as err:
if err.errno == 11:
print ( "No motion detected")
continue
os.close(file)
It works fine, if there is no motion the message is printed out but, in case of motion the output I get is quite different from the "vanilla" mode.