--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/symbian-qemu-0.9.1-12/python-2.6.1/Demo/threads/sync.py Fri Jul 31 15:01:17 2009 +0100
@@ -0,0 +1,603 @@
+# Defines classes that provide synchronization objects. Note that use of
+# this module requires that your Python support threads.
+#
+# condition(lock=None) # a POSIX-like condition-variable object
+# barrier(n) # an n-thread barrier
+# event() # an event object
+# semaphore(n=1) # a semaphore object, with initial count n
+# mrsw() # a multiple-reader single-writer lock
+#
+# CONDITIONS
+#
+# A condition object is created via
+# import this_module
+# your_condition_object = this_module.condition(lock=None)
+#
+# As explained below, a condition object has a lock associated with it,
+# used in the protocol to protect condition data. You can specify a
+# lock to use in the constructor, else the constructor will allocate
+# an anonymous lock for you. Specifying a lock explicitly can be useful
+# when more than one condition keys off the same set of shared data.
+#
+# Methods:
+# .acquire()
+# acquire the lock associated with the condition
+# .release()
+# release the lock associated with the condition
+# .wait()
+# block the thread until such time as some other thread does a
+# .signal or .broadcast on the same condition, and release the
+# lock associated with the condition. The lock associated with
+# the condition MUST be in the acquired state at the time
+# .wait is invoked.
+# .signal()
+# wake up exactly one thread (if any) that previously did a .wait
+# on the condition; that thread will awaken with the lock associated
+# with the condition in the acquired state. If no threads are
+# .wait'ing, this is a nop. If more than one thread is .wait'ing on
+# the condition, any of them may be awakened.
+# .broadcast()
+# wake up all threads (if any) that are .wait'ing on the condition;
+# the threads are woken up serially, each with the lock in the
+# acquired state, so should .release() as soon as possible. If no
+# threads are .wait'ing, this is a nop.
+#
+# Note that if a thread does a .wait *while* a signal/broadcast is
+# in progress, it's guaranteeed to block until a subsequent
+# signal/broadcast.
+#
+# Secret feature: `broadcast' actually takes an integer argument,
+# and will wake up exactly that many waiting threads (or the total
+# number waiting, if that's less). Use of this is dubious, though,
+# and probably won't be supported if this form of condition is
+# reimplemented in C.
+#
+# DIFFERENCES FROM POSIX
+#
+# + A separate mutex is not needed to guard condition data. Instead, a
+# condition object can (must) be .acquire'ed and .release'ed directly.
+# This eliminates a common error in using POSIX conditions.
+#
+# + Because of implementation difficulties, a POSIX `signal' wakes up
+# _at least_ one .wait'ing thread. Race conditions make it difficult
+# to stop that. This implementation guarantees to wake up only one,
+# but you probably shouldn't rely on that.
+#
+# PROTOCOL
+#
+# Condition objects are used to block threads until "some condition" is
+# true. E.g., a thread may wish to wait until a producer pumps out data
+# for it to consume, or a server may wish to wait until someone requests
+# its services, or perhaps a whole bunch of threads want to wait until a
+# preceding pass over the data is complete. Early models for conditions
+# relied on some other thread figuring out when a blocked thread's
+# condition was true, and made the other thread responsible both for
+# waking up the blocked thread and guaranteeing that it woke up with all
+# data in a correct state. This proved to be very delicate in practice,
+# and gave conditions a bad name in some circles.
+#
+# The POSIX model addresses these problems by making a thread responsible
+# for ensuring that its own state is correct when it wakes, and relies
+# on a rigid protocol to make this easy; so long as you stick to the
+# protocol, POSIX conditions are easy to "get right":
+#
+# A) The thread that's waiting for some arbitrarily-complex condition
+# (ACC) to become true does:
+#
+# condition.acquire()
+# while not (code to evaluate the ACC):
+# condition.wait()
+# # That blocks the thread, *and* releases the lock. When a
+# # condition.signal() happens, it will wake up some thread that
+# # did a .wait, *and* acquire the lock again before .wait
+# # returns.
+# #
+# # Because the lock is acquired at this point, the state used
+# # in evaluating the ACC is frozen, so it's safe to go back &
+# # reevaluate the ACC.
+#
+# # At this point, ACC is true, and the thread has the condition
+# # locked.
+# # So code here can safely muck with the shared state that
+# # went into evaluating the ACC -- if it wants to.
+# # When done mucking with the shared state, do
+# condition.release()
+#
+# B) Threads that are mucking with shared state that may affect the
+# ACC do:
+#
+# condition.acquire()
+# # muck with shared state
+# condition.release()
+# if it's possible that ACC is true now:
+# condition.signal() # or .broadcast()
+#
+# Note: You may prefer to put the "if" clause before the release().
+# That's fine, but do note that anyone waiting on the signal will
+# stay blocked until the release() is done (since acquiring the
+# condition is part of what .wait() does before it returns).
+#
+# TRICK OF THE TRADE
+#
+# With simpler forms of conditions, it can be impossible to know when
+# a thread that's supposed to do a .wait has actually done it. But
+# because this form of condition releases a lock as _part_ of doing a
+# wait, the state of that lock can be used to guarantee it.
+#
+# E.g., suppose thread A spawns thread B and later wants to wait for B to
+# complete:
+#
+# In A: In B:
+#
+# B_done = condition() ... do work ...
+# B_done.acquire() B_done.acquire(); B_done.release()
+# spawn B B_done.signal()
+# ... some time later ... ... and B exits ...
+# B_done.wait()
+#
+# Because B_done was in the acquire'd state at the time B was spawned,
+# B's attempt to acquire B_done can't succeed until A has done its
+# B_done.wait() (which releases B_done). So B's B_done.signal() is
+# guaranteed to be seen by the .wait(). Without the lock trick, B
+# may signal before A .waits, and then A would wait forever.
+#
+# BARRIERS
+#
+# A barrier object is created via
+# import this_module
+# your_barrier = this_module.barrier(num_threads)
+#
+# Methods:
+# .enter()
+# the thread blocks until num_threads threads in all have done
+# .enter(). Then the num_threads threads that .enter'ed resume,
+# and the barrier resets to capture the next num_threads threads
+# that .enter it.
+#
+# EVENTS
+#
+# An event object is created via
+# import this_module
+# your_event = this_module.event()
+#
+# An event has two states, `posted' and `cleared'. An event is
+# created in the cleared state.
+#
+# Methods:
+#
+# .post()
+# Put the event in the posted state, and resume all threads
+# .wait'ing on the event (if any).
+#
+# .clear()
+# Put the event in the cleared state.
+#
+# .is_posted()
+# Returns 0 if the event is in the cleared state, or 1 if the event
+# is in the posted state.
+#
+# .wait()
+# If the event is in the posted state, returns immediately.
+# If the event is in the cleared state, blocks the calling thread
+# until the event is .post'ed by another thread.
+#
+# Note that an event, once posted, remains posted until explicitly
+# cleared. Relative to conditions, this is both the strength & weakness
+# of events. It's a strength because the .post'ing thread doesn't have to
+# worry about whether the threads it's trying to communicate with have
+# already done a .wait (a condition .signal is seen only by threads that
+# do a .wait _prior_ to the .signal; a .signal does not persist). But
+# it's a weakness because .clear'ing an event is error-prone: it's easy
+# to mistakenly .clear an event before all the threads you intended to
+# see the event get around to .wait'ing on it. But so long as you don't
+# need to .clear an event, events are easy to use safely.
+#
+# SEMAPHORES
+#
+# A semaphore object is created via
+# import this_module
+# your_semaphore = this_module.semaphore(count=1)
+#
+# A semaphore has an integer count associated with it. The initial value
+# of the count is specified by the optional argument (which defaults to
+# 1) passed to the semaphore constructor.
+#
+# Methods:
+#
+# .p()
+# If the semaphore's count is greater than 0, decrements the count
+# by 1 and returns.
+# Else if the semaphore's count is 0, blocks the calling thread
+# until a subsequent .v() increases the count. When that happens,
+# the count will be decremented by 1 and the calling thread resumed.
+#
+# .v()
+# Increments the semaphore's count by 1, and wakes up a thread (if
+# any) blocked by a .p(). It's an (detected) error for a .v() to
+# increase the semaphore's count to a value larger than the initial
+# count.
+#
+# MULTIPLE-READER SINGLE-WRITER LOCKS
+#
+# A mrsw lock is created via
+# import this_module
+# your_mrsw_lock = this_module.mrsw()
+#
+# This kind of lock is often useful with complex shared data structures.
+# The object lets any number of "readers" proceed, so long as no thread
+# wishes to "write". When a (one or more) thread declares its intention
+# to "write" (e.g., to update a shared structure), all current readers
+# are allowed to finish, and then a writer gets exclusive access; all
+# other readers & writers are blocked until the current writer completes.
+# Finally, if some thread is waiting to write and another is waiting to
+# read, the writer takes precedence.
+#
+# Methods:
+#
+# .read_in()
+# If no thread is writing or waiting to write, returns immediately.
+# Else blocks until no thread is writing or waiting to write. So
+# long as some thread has completed a .read_in but not a .read_out,
+# writers are blocked.
+#
+# .read_out()
+# Use sometime after a .read_in to declare that the thread is done
+# reading. When all threads complete reading, a writer can proceed.
+#
+# .write_in()
+# If no thread is writing (has completed a .write_in, but hasn't yet
+# done a .write_out) or reading (similarly), returns immediately.
+# Else blocks the calling thread, and threads waiting to read, until
+# the current writer completes writing or all the current readers
+# complete reading; if then more than one thread is waiting to
+# write, one of them is allowed to proceed, but which one is not
+# specified.
+#
+# .write_out()
+# Use sometime after a .write_in to declare that the thread is done
+# writing. Then if some other thread is waiting to write, it's
+# allowed to proceed. Else all threads (if any) waiting to read are
+# allowed to proceed.
+#
+# .write_to_read()
+# Use instead of a .write_in to declare that the thread is done
+# writing but wants to continue reading without other writers
+# intervening. If there are other threads waiting to write, they
+# are allowed to proceed only if the current thread calls
+# .read_out; threads waiting to read are only allowed to proceed
+# if there are are no threads waiting to write. (This is a
+# weakness of the interface!)
+
+import thread
+
+class condition:
+ def __init__(self, lock=None):
+ # the lock actually used by .acquire() and .release()
+ if lock is None:
+ self.mutex = thread.allocate_lock()
+ else:
+ if hasattr(lock, 'acquire') and \
+ hasattr(lock, 'release'):
+ self.mutex = lock
+ else:
+ raise TypeError, 'condition constructor requires ' \
+ 'a lock argument'
+
+ # lock used to block threads until a signal
+ self.checkout = thread.allocate_lock()
+ self.checkout.acquire()
+
+ # internal critical-section lock, & the data it protects
+ self.idlock = thread.allocate_lock()
+ self.id = 0
+ self.waiting = 0 # num waiters subject to current release
+ self.pending = 0 # num waiters awaiting next signal
+ self.torelease = 0 # num waiters to release
+ self.releasing = 0 # 1 iff release is in progress
+
+ def acquire(self):
+ self.mutex.acquire()
+
+ def release(self):
+ self.mutex.release()
+
+ def wait(self):
+ mutex, checkout, idlock = self.mutex, self.checkout, self.idlock
+ if not mutex.locked():
+ raise ValueError, \
+ "condition must be .acquire'd when .wait() invoked"
+
+ idlock.acquire()
+ myid = self.id
+ self.pending = self.pending + 1
+ idlock.release()
+
+ mutex.release()
+
+ while 1:
+ checkout.acquire(); idlock.acquire()
+ if myid < self.id:
+ break
+ checkout.release(); idlock.release()
+
+ self.waiting = self.waiting - 1
+ self.torelease = self.torelease - 1
+ if self.torelease:
+ checkout.release()
+ else:
+ self.releasing = 0
+ if self.waiting == self.pending == 0:
+ self.id = 0
+ idlock.release()
+ mutex.acquire()
+
+ def signal(self):
+ self.broadcast(1)
+
+ def broadcast(self, num = -1):
+ if num < -1:
+ raise ValueError, '.broadcast called with num %r' % (num,)
+ if num == 0:
+ return
+ self.idlock.acquire()
+ if self.pending:
+ self.waiting = self.waiting + self.pending
+ self.pending = 0
+ self.id = self.id + 1
+ if num == -1:
+ self.torelease = self.waiting
+ else:
+ self.torelease = min( self.waiting,
+ self.torelease + num )
+ if self.torelease and not self.releasing:
+ self.releasing = 1
+ self.checkout.release()
+ self.idlock.release()
+
+class barrier:
+ def __init__(self, n):
+ self.n = n
+ self.togo = n
+ self.full = condition()
+
+ def enter(self):
+ full = self.full
+ full.acquire()
+ self.togo = self.togo - 1
+ if self.togo:
+ full.wait()
+ else:
+ self.togo = self.n
+ full.broadcast()
+ full.release()
+
+class event:
+ def __init__(self):
+ self.state = 0
+ self.posted = condition()
+
+ def post(self):
+ self.posted.acquire()
+ self.state = 1
+ self.posted.broadcast()
+ self.posted.release()
+
+ def clear(self):
+ self.posted.acquire()
+ self.state = 0
+ self.posted.release()
+
+ def is_posted(self):
+ self.posted.acquire()
+ answer = self.state
+ self.posted.release()
+ return answer
+
+ def wait(self):
+ self.posted.acquire()
+ if not self.state:
+ self.posted.wait()
+ self.posted.release()
+
+class semaphore:
+ def __init__(self, count=1):
+ if count <= 0:
+ raise ValueError, 'semaphore count %d; must be >= 1' % count
+ self.count = count
+ self.maxcount = count
+ self.nonzero = condition()
+
+ def p(self):
+ self.nonzero.acquire()
+ while self.count == 0:
+ self.nonzero.wait()
+ self.count = self.count - 1
+ self.nonzero.release()
+
+ def v(self):
+ self.nonzero.acquire()
+ if self.count == self.maxcount:
+ raise ValueError, '.v() tried to raise semaphore count above ' \
+ 'initial value %r' % self.maxcount
+ self.count = self.count + 1
+ self.nonzero.signal()
+ self.nonzero.release()
+
+class mrsw:
+ def __init__(self):
+ # critical-section lock & the data it protects
+ self.rwOK = thread.allocate_lock()
+ self.nr = 0 # number readers actively reading (not just waiting)
+ self.nw = 0 # number writers either waiting to write or writing
+ self.writing = 0 # 1 iff some thread is writing
+
+ # conditions
+ self.readOK = condition(self.rwOK) # OK to unblock readers
+ self.writeOK = condition(self.rwOK) # OK to unblock writers
+
+ def read_in(self):
+ self.rwOK.acquire()
+ while self.nw:
+ self.readOK.wait()
+ self.nr = self.nr + 1
+ self.rwOK.release()
+
+ def read_out(self):
+ self.rwOK.acquire()
+ if self.nr <= 0:
+ raise ValueError, \
+ '.read_out() invoked without an active reader'
+ self.nr = self.nr - 1
+ if self.nr == 0:
+ self.writeOK.signal()
+ self.rwOK.release()
+
+ def write_in(self):
+ self.rwOK.acquire()
+ self.nw = self.nw + 1
+ while self.writing or self.nr:
+ self.writeOK.wait()
+ self.writing = 1
+ self.rwOK.release()
+
+ def write_out(self):
+ self.rwOK.acquire()
+ if not self.writing:
+ raise ValueError, \
+ '.write_out() invoked without an active writer'
+ self.writing = 0
+ self.nw = self.nw - 1
+ if self.nw:
+ self.writeOK.signal()
+ else:
+ self.readOK.broadcast()
+ self.rwOK.release()
+
+ def write_to_read(self):
+ self.rwOK.acquire()
+ if not self.writing:
+ raise ValueError, \
+ '.write_to_read() invoked without an active writer'
+ self.writing = 0
+ self.nw = self.nw - 1
+ self.nr = self.nr + 1
+ if not self.nw:
+ self.readOK.broadcast()
+ self.rwOK.release()
+
+# The rest of the file is a test case, that runs a number of parallelized
+# quicksorts in parallel. If it works, you'll get about 600 lines of
+# tracing output, with a line like
+# test passed! 209 threads created in all
+# as the last line. The content and order of preceding lines will
+# vary across runs.
+
+def _new_thread(func, *args):
+ global TID
+ tid.acquire(); id = TID = TID+1; tid.release()
+ io.acquire(); alive.append(id); \
+ print 'starting thread', id, '--', len(alive), 'alive'; \
+ io.release()
+ thread.start_new_thread( func, (id,) + args )
+
+def _qsort(tid, a, l, r, finished):
+ # sort a[l:r]; post finished when done
+ io.acquire(); print 'thread', tid, 'qsort', l, r; io.release()
+ if r-l > 1:
+ pivot = a[l]
+ j = l+1 # make a[l:j] <= pivot, and a[j:r] > pivot
+ for i in range(j, r):
+ if a[i] <= pivot:
+ a[j], a[i] = a[i], a[j]
+ j = j + 1
+ a[l], a[j-1] = a[j-1], pivot
+
+ l_subarray_sorted = event()
+ r_subarray_sorted = event()
+ _new_thread(_qsort, a, l, j-1, l_subarray_sorted)
+ _new_thread(_qsort, a, j, r, r_subarray_sorted)
+ l_subarray_sorted.wait()
+ r_subarray_sorted.wait()
+
+ io.acquire(); print 'thread', tid, 'qsort done'; \
+ alive.remove(tid); io.release()
+ finished.post()
+
+def _randarray(tid, a, finished):
+ io.acquire(); print 'thread', tid, 'randomizing array'; \
+ io.release()
+ for i in range(1, len(a)):
+ wh.acquire(); j = randint(0,i); wh.release()
+ a[i], a[j] = a[j], a[i]
+ io.acquire(); print 'thread', tid, 'randomizing done'; \
+ alive.remove(tid); io.release()
+ finished.post()
+
+def _check_sort(a):
+ if a != range(len(a)):
+ raise ValueError, ('a not sorted', a)
+
+def _run_one_sort(tid, a, bar, done):
+ # randomize a, and quicksort it
+ # for variety, all the threads running this enter a barrier
+ # at the end, and post `done' after the barrier exits
+ io.acquire(); print 'thread', tid, 'randomizing', a; \
+ io.release()
+ finished = event()
+ _new_thread(_randarray, a, finished)
+ finished.wait()
+
+ io.acquire(); print 'thread', tid, 'sorting', a; io.release()
+ finished.clear()
+ _new_thread(_qsort, a, 0, len(a), finished)
+ finished.wait()
+ _check_sort(a)
+
+ io.acquire(); print 'thread', tid, 'entering barrier'; \
+ io.release()
+ bar.enter()
+ io.acquire(); print 'thread', tid, 'leaving barrier'; \
+ io.release()
+ io.acquire(); alive.remove(tid); io.release()
+ bar.enter() # make sure they've all removed themselves from alive
+ ## before 'done' is posted
+ bar.enter() # just to be cruel
+ done.post()
+
+def test():
+ global TID, tid, io, wh, randint, alive
+ import random
+ randint = random.randint
+
+ TID = 0 # thread ID (1, 2, ...)
+ tid = thread.allocate_lock() # for changing TID
+ io = thread.allocate_lock() # for printing, and 'alive'
+ wh = thread.allocate_lock() # for calls to random
+ alive = [] # IDs of active threads
+
+ NSORTS = 5
+ arrays = []
+ for i in range(NSORTS):
+ arrays.append( range( (i+1)*10 ) )
+
+ bar = barrier(NSORTS)
+ finished = event()
+ for i in range(NSORTS):
+ _new_thread(_run_one_sort, arrays[i], bar, finished)
+ finished.wait()
+
+ print 'all threads done, and checking results ...'
+ if alive:
+ raise ValueError, ('threads still alive at end', alive)
+ for i in range(NSORTS):
+ a = arrays[i]
+ if len(a) != (i+1)*10:
+ raise ValueError, ('length of array', i, 'screwed up')
+ _check_sort(a)
+
+ print 'test passed!', TID, 'threads created in all'
+
+if __name__ == '__main__':
+ test()
+
+# end of module