ref: 19cc46bc5ee1dd43537c4094d19d8da778b72bce
dir: /sys/src/cmd/python/Demo/metaclasses/Synch.py/
"""Synchronization metaclass.
This metaclass makes it possible to declare synchronized methods.
"""
import thread
# First we need to define a reentrant lock.
# This is generally useful and should probably be in a standard Python
# library module. For now, we in-line it.
class Lock:
"""Reentrant lock.
This is a mutex-like object which can be acquired by the same
thread more than once. It keeps a reference count of the number
of times it has been acquired by the same thread. Each acquire()
call must be matched by a release() call and only the last
release() call actually releases the lock for acquisition by
another thread.
The implementation uses two locks internally:
__mutex is a short term lock used to protect the instance variables
__wait is the lock for which other threads wait
A thread intending to acquire both locks should acquire __wait
first.
The implementation uses two other instance variables, protected by
locking __mutex:
__tid is the thread ID of the thread that currently has the lock
__count is the number of times the current thread has acquired it
When the lock is released, __tid is None and __count is zero.
"""
def __init__(self):
"""Constructor. Initialize all instance variables."""
self.__mutex = thread.allocate_lock()
self.__wait = thread.allocate_lock()
self.__tid = None
self.__count = 0
def acquire(self, flag=1):
"""Acquire the lock.
If the optional flag argument is false, returns immediately
when it cannot acquire the __wait lock without blocking (it
may still block for a little while in order to acquire the
__mutex lock).
The return value is only relevant when the flag argument is
false; it is 1 if the lock is acquired, 0 if not.
"""
self.__mutex.acquire()
try:
if self.__tid == thread.get_ident():
self.__count = self.__count + 1
return 1
finally:
self.__mutex.release()
locked = self.__wait.acquire(flag)
if not flag and not locked:
return 0
try:
self.__mutex.acquire()
assert self.__tid == None
assert self.__count == 0
self.__tid = thread.get_ident()
self.__count = 1
return 1
finally:
self.__mutex.release()
def release(self):
"""Release the lock.
If this thread doesn't currently have the lock, an assertion
error is raised.
Only allow another thread to acquire the lock when the count
reaches zero after decrementing it.
"""
self.__mutex.acquire()
try:
assert self.__tid == thread.get_ident()
assert self.__count > 0
self.__count = self.__count - 1
if self.__count == 0:
self.__tid = None
self.__wait.release()
finally:
self.__mutex.release()
def _testLock():
done = []
def f2(lock, done=done):
lock.acquire()
print "f2 running in thread %d\n" % thread.get_ident(),
lock.release()
done.append(1)
def f1(lock, f2=f2, done=done):
lock.acquire()
print "f1 running in thread %d\n" % thread.get_ident(),
try:
f2(lock)
finally:
lock.release()
done.append(1)
lock = Lock()
lock.acquire()
f1(lock) # Adds 2 to done
lock.release()
lock.acquire()
thread.start_new_thread(f1, (lock,)) # Adds 2
thread.start_new_thread(f1, (lock, f1)) # Adds 3
thread.start_new_thread(f2, (lock,)) # Adds 1
thread.start_new_thread(f2, (lock,)) # Adds 1
lock.release()
import time
while len(done) < 9:
print len(done)
time.sleep(0.001)
print len(done)
# Now, the Locking metaclass is a piece of cake.
# As an example feature, methods whose name begins with exactly one
# underscore are not synchronized.
from Meta import MetaClass, MetaHelper, MetaMethodWrapper
class LockingMethodWrapper(MetaMethodWrapper):
def __call__(self, *args, **kw):
if self.__name__[:1] == '_' and self.__name__[1:] != '_':
return apply(self.func, (self.inst,) + args, kw)
self.inst.__lock__.acquire()
try:
return apply(self.func, (self.inst,) + args, kw)
finally:
self.inst.__lock__.release()
class LockingHelper(MetaHelper):
__methodwrapper__ = LockingMethodWrapper
def __helperinit__(self, formalclass):
MetaHelper.__helperinit__(self, formalclass)
self.__lock__ = Lock()
class LockingMetaClass(MetaClass):
__helper__ = LockingHelper
Locking = LockingMetaClass('Locking', (), {})
def _test():
# For kicks, take away the Locking base class and see it die
class Buffer(Locking):
def __init__(self, initialsize):
assert initialsize > 0
self.size = initialsize
self.buffer = [None]*self.size
self.first = self.last = 0
def put(self, item):
# Do we need to grow the buffer?
if (self.last+1) % self.size != self.first:
# Insert the new item
self.buffer[self.last] = item
self.last = (self.last+1) % self.size
return
# Double the buffer size
# First normalize it so that first==0 and last==size-1
print "buffer =", self.buffer
print "first = %d, last = %d, size = %d" % (
self.first, self.last, self.size)
if self.first <= self.last:
temp = self.buffer[self.first:self.last]
else:
temp = self.buffer[self.first:] + self.buffer[:self.last]
print "temp =", temp
self.buffer = temp + [None]*(self.size+1)
self.first = 0
self.last = self.size-1
self.size = self.size*2
print "Buffer size doubled to", self.size
print "new buffer =", self.buffer
print "first = %d, last = %d, size = %d" % (
self.first, self.last, self.size)
self.put(item) # Recursive call to test the locking
def get(self):
# Is the buffer empty?
if self.first == self.last:
raise EOFError # Avoid defining a new exception
item = self.buffer[self.first]
self.first = (self.first+1) % self.size
return item
def producer(buffer, wait, n=1000):
import time
i = 0
while i < n:
print "put", i
buffer.put(i)
i = i+1
print "Producer: done producing", n, "items"
wait.release()
def consumer(buffer, wait, n=1000):
import time
i = 0
tout = 0.001
while i < n:
try:
x = buffer.get()
if x != i:
raise AssertionError, \
"get() returned %s, expected %s" % (x, i)
print "got", i
i = i+1
tout = 0.001
except EOFError:
time.sleep(tout)
tout = tout*2
print "Consumer: done consuming", n, "items"
wait.release()
pwait = thread.allocate_lock()
pwait.acquire()
cwait = thread.allocate_lock()
cwait.acquire()
buffer = Buffer(1)
n = 1000
thread.start_new_thread(consumer, (buffer, cwait, n))
thread.start_new_thread(producer, (buffer, pwait, n))
pwait.acquire()
print "Producer done"
cwait.acquire()
print "All done"
print "buffer size ==", len(buffer.buffer)
if __name__ == '__main__':
_testLock()
_test()