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| -rw-r--r-- | Demo/threads/README | 1 | ||||
| -rw-r--r-- | Demo/threads/bug.py | 69 |
2 files changed, 0 insertions, 70 deletions
diff --git a/Demo/threads/README b/Demo/threads/README index fe27818..fee6aad 100644 --- a/Demo/threads/README +++ b/Demo/threads/README @@ -3,7 +3,6 @@ This directory contains some demonstrations of the thread module. These are mostly "proof of concept" type applications: Generator.py Generator class implemented with threads. -bug.py Demonstrate a bug with importing modules in threads. find.py Parallelized "find(1)" (looks for directories). sync.py Condition variables primitives by Tim Peters. telnet.py Version of ../sockets/telnet.py using threads. diff --git a/Demo/threads/bug.py b/Demo/threads/bug.py deleted file mode 100644 index 6c5edac..0000000 --- a/Demo/threads/bug.py +++ /dev/null @@ -1,69 +0,0 @@ -# The following self-contained little program usually freezes with most -# threads reporting -# -# Unhandled exception in thread: -# Traceback (innermost last): -# File "importbug.py", line 6 -# x = whrandom.randint(1,3) -# AttributeError: randint -# -# Here's the program; it doesn't use anything from the attached module: - -import thread - -def task(): - global N - import whrandom - x = whrandom.randint(1,3) - a.acquire() - N = N - 1 - if N == 0: done.release() - a.release() - -a = thread.allocate_lock() -done = thread.allocate_lock() -N = 10 - -done.acquire() -for i in range(N): - thread.start_new_thread(task, ()) -done.acquire() -print 'done' - - -# Sticking an acquire/release pair around the 'import' statement makes the -# problem go away. -# -# I believe that what happens is: -# -# 1) The first thread to hit the import atomically reaches, and executes -# most of, get_module. In particular, it finds Lib/whrandom.pyc, -# installs its name in sys.modules, and executes -# -# v = eval_code(co, d, d, d, (object *)NULL); -# -# to initialize the module. -# -# 2) eval_code "ticker"-slices the 1st thread out, and gives another thread -# a chance. When this 2nd thread hits the same 'import', import_module -# finds 'whrandom' in sys.modules, so just proceeds. -# -# 3) But the 1st thread is still "in the middle" of executing whrandom.pyc. -# So the 2nd thread has a good chance of trying to look up 'randint' -# before the 1st thread has placed it in whrandom's dict. -# -# 4) The more threads there are, the more likely that at least one of them -# will do this before the 1st thread finishes the import work. -# -# If that's right, a perhaps not-too-bad workaround would be to introduce a -# static "you can't interrupt this thread" flag in ceval.c, check it before -# giving up interpreter_lock, and have IMPORT_NAME set it & restore (plain -# clearing would not work) it around its call to import_module. To its -# credit, there's something wonderfully perverse about fixing a race via an -# unprotected static <grin>. -# -# as-with-most-other-things-(pseudo-)parallel-programming's-more-fun- -# in-python-too!-ly y'rs - tim -# -# Tim Peters tim@ksr.com -# not speaking for Kendall Square Research Corp |