import threading

class SharedCounter:
    '''
    A counter object that can be shared by multiple threads.
    '''
    def __init__(self, initial_value = 0):
        self._value = initial_value
        self._value_lock = threading.Lock()

    def inc_r(self,delta=1):
        '''
        Increment the counter with locking
        '''
        with self._value_lock:
             self._value += delta

    def dec_r(self,delta=1):
        '''
        Decrement the counter with locking
        '''
        with self._value_lock:
             self._value -= delta

import threading

class SharedCounter:
    '''
    A counter object that can be shared by multiple threads.
    '''
    def __init__(self, initial_value = 0):
        self._value = initial_value
        self._value_lock = threading.Lock()

    def inc_r(self,delta=1):
        '''
        Increment the counter with locking
        '''
        self._value_lock.acquire()
        self._value += delta
        self._value_lock.release()

    def dec_r(self,delta=1):
        '''
        Decrement the counter with locking
        '''
        self._value_lock.acquire()
        self._value -= delta
        self._value_lock.release()

import threading

class SharedCounter:
    '''
    A counter object that can be shared by multiple threads.
    '''
    _lock = threading.RLock()
    def __init__(self, initial_value = 0):
        self._value = initial_value

    def inc_r(self,delta=1):
        '''
        Increment the counter with locking
        '''
        with SharedCounter._lock:
            self._value += delta

    def dec_r(self,delta=1):
        '''
        Decrement the counter with locking
        '''
        with SharedCounter._lock:
             self.inc_r(-delta)

from threading import Semaphore
import urllib.request

# At most, five threads allowed to run at once
_fetch_url_sema = Semaphore(5)

def fetch_url(url):
    with _fetch_url_sema:
        return urllib.request.urlopen(url)

import threading
from contextlib import contextmanager

_local = threading.local()

@contextmanager
def acquire(*locks):
    # Sort locks by object identifier
    locks = sorted(locks, key=lambda x: id(x))

    # Make sure lock order of previously acquired locks is not violated
    acquired = getattr(_local,'acquired',[])
    if acquired and max(id(lock) for lock in acquired) >= id(locks[0]):
        raise RuntimeError('Lock Order Violation')

    # Acquire all of the locks
    acquired.extend(locks)
    _local.acquired = acquired

    try:
        for lock in locks:
            lock.acquire()
        yield
    finally:
        # Release locks in reverse order of acquisition
        for lock in reversed(locks):
            lock.release()
        del acquired[-len(locks):]

import threading
from chapter12.avoid_lock_1 import acquire

x_lock = threading.Lock()
y_lock = threading.Lock()

def thread_1():
    while True:
        with acquire(x_lock, y_lock):
            print('Thread-1')

def thread_2():
    while True:
        with acquire(y_lock, x_lock):
            print('Thread-2')

t1 = threading.Thread(target=thread_1)
t1.daemon = True
t1.start()

t2 = threading.Thread(target=thread_2)
t2.daemon = True
t2.start()

import threading
from chapter12.avoid_lock_1 import acquire

x_lock = threading.Lock()
y_lock = threading.Lock()

def thread_1():

    while True:
        with acquire(x_lock):
            with acquire(y_lock):
                print('Thread-1')

def thread_2():
    while True:
        with acquire(y_lock):
            with acquire(x_lock):
                print('Thread-2')

t1 = threading.Thread(target=thread_1)
t1.daemon = True
t1.start()

t2 = threading.Thread(target=thread_2)
t2.daemon = True
t2.start()

import threading
from chapter12.avoid_lock_1 import acquire

# The philosopher thread
def philosopher(left, right):
    while True:
        with acquire(left,right):
             print(f'{threading.currentThread()} eating')

# The chopsticks (represented by locks)
NSTICKS = 5
chopsticks = [threading.Lock() for n in range(NSTICKS)]

# Create all of the philosophers
for n in range(NSTICKS):
    t = threading.Thread(target=philosopher,
                         args=(chopsticks[n],chopsticks[(n+1) % NSTICKS]))
    t.start()