FCL/sf/adapt/qemu: comparison symbian-qemu-0.9.1-12/python-2.6.1/Demo/threads/sync.py

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-:ffa851df0825
+:2fb8b9db1c86
+# 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