#$@%#$%!

Ngiler SH3LL 360
: / lib64 / python2.7 / Demo / threads /

Information Server
MySQL : OFF Perl : OFF CURL : ON WGET : OFF PKEXEC : OFF

Directive	Local Value
IP Address	162.0.209.101
System	Linux premium169.web-hosting.com 4.18.0-553.50.1.lve.el8.x86_64 #1 SMP Thu Apr 17 19:10:24 UTC 2025 x86_64
User	luxeelil
PHP Version	8.0.30
Software	LiteSpeed
Doc root	Writable

Edit File : sync.py \| Size : 21.15 KB
# 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 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 Back

Edit File : sync.py | Size : 21.15 KB

# 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 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

Back