import threading
import sys
import time
import random
"""
Shared class contains resources to resolv H2O problem
It has
- two integers to count hydrogen and oxygen particles
- two locks to make all integers operations atomic
- return, increment, and decrement are executed atomically using these locks
- two semaphores to stop particles when it is not possible to make water
"""
class Shared:
def __init__( self ): # Constructor
self.cH = 0
self.cO = 0
self.SemH = threading.Semaphore( 0 )
self.SemO = threading.Semaphore( 0 )
self.lockH = threading.Lock()
self.lockO = threading.Lock()
def getH( self ):
with self.lockH: # Only one thread can pass this lock
return self.cH
def getO( self ):
with self.lockO:
return self.cO
def decH( self ):
with self.lockH:
self.cH -= 1
def decO( self ):
with self.lockO:
self.cO -= 1
def incH( self ):
with self.lockH:
self.cH += 1
def incO( self ):
with self.lockO:
self.cO += 1
def signalH( self ):
self.SemH.release()
def signalO( self ):
self.SemO.release()
def waitH( self ):
self.SemH.acquire()
def waitO( self ):
self.SemO.acquire()
"""
Agua is where all particles are created using a thread for each one
It is an extension for the threading.Thread class and we need to overcharge constructor and run methods
"""
class Agua ( threading.Thread ):
def __init__( self, threadID, resources ):
threading.Thread.__init__( self )
self.threadID = threadID
self.resources = resources
def run(self): # Create randomly hydrogens and oxygens
r = random.randint( 1, 1000 )
if ( 0 == (r % 3) ):
print( "Starting O thread " + str( self.threadID ) + " ... cO(" + str(self.resources.getO()) + "), cH(" + str(self.resources.getH()) + ")" )
self.O()
else:
print( "Starting H thread " + str( self.threadID ) + " ... cO(" + str(self.resources.getO()) + "), cH(" + str(self.resources.getH()) + ")" )
self.H()
def H( self ): # Represent an hydrogen particle
if ( (self.resources.getO() > 0) and (self.resources.getH() > 0) ):
print( "\tH particle making water :) ... " + str( self.threadID ) + " ... cO(" + str(self.resources.getO()) + "), cH(" + str(self.resources.getH()) + ")" )
self.resources.decH()
self.resources.decO()
self.resources.signalO()
self.resources.signalH()
else:
self.resources.incH()
self.resources.waitH()
def O( self ): # Represent an oxygen particle
if ( self.resources.getH() > 1 ):
print( "\tO particle making water :) ... " + str( self.threadID ) + " ... cO(" + str(self.resources.getO()) + "), cH(" + str(self.resources.getH()) + ")" )
self.resources.decH()
self.resources.decH()
self.resources.signalH()
self.resources.signalH()
else:
self.resources.incO()
self.resources.waitO()
def main():
threads = []
resources = Shared();
for i in range( 100 ):
t = Agua( i, resources )
threads.append( t )
t.start()
for t in threads:
t.join()
if __name__ == "__main__":
main()
