Mercurial > cpython-lru_cache-weakref
annotate Demo/threads/bug.py @ 25838:8540887bcec6 2.2
Backport of 2.183:
Fix memory leak in add_subclass() found by NealN with valgrind.
| author | Guido van Rossum <guido@python.org> |
|---|---|
| date | Fri, 18 Oct 2002 13:42:21 +0000 |
| parents | 50bbe811b344 |
| children |
| rev | line source |
|---|---|
| 1637 | 1 # The following self-contained little program usually freezes with most |
| 2 # threads reporting | |
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16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
3 # |
| 1637 | 4 # Unhandled exception in thread: |
| 5 # Traceback (innermost last): | |
| 6 # File "importbug.py", line 6 | |
| 7 # x = whrandom.randint(1,3) | |
| 8 # AttributeError: randint | |
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16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
9 # |
| 1637 | 10 # Here's the program; it doesn't use anything from the attached module: |
| 11 | |
| 12 import thread | |
| 13 | |
| 14 def task(): | |
| 15 global N | |
| 16 import whrandom | |
| 17 x = whrandom.randint(1,3) | |
| 18 a.acquire() | |
| 19 N = N - 1 | |
| 20 if N == 0: done.release() | |
| 21 a.release() | |
| 22 | |
| 23 a = thread.allocate_lock() | |
| 24 done = thread.allocate_lock() | |
| 25 N = 10 | |
| 26 | |
| 27 done.acquire() | |
| 28 for i in range(N): | |
| 29 thread.start_new_thread(task, ()) | |
| 30 done.acquire() | |
| 31 print 'done' | |
| 32 | |
| 33 | |
| 34 # Sticking an acquire/release pair around the 'import' statement makes the | |
| 35 # problem go away. | |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
36 # |
| 1637 | 37 # I believe that what happens is: |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
38 # |
| 1637 | 39 # 1) The first thread to hit the import atomically reaches, and executes |
| 40 # most of, get_module. In particular, it finds Lib/whrandom.pyc, | |
| 41 # installs its name in sys.modules, and executes | |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
42 # |
| 1637 | 43 # v = eval_code(co, d, d, d, (object *)NULL); |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
44 # |
| 1637 | 45 # to initialize the module. |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
46 # |
| 1637 | 47 # 2) eval_code "ticker"-slices the 1st thread out, and gives another thread |
| 48 # a chance. When this 2nd thread hits the same 'import', import_module | |
| 49 # finds 'whrandom' in sys.modules, so just proceeds. | |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
50 # |
| 1637 | 51 # 3) But the 1st thread is still "in the middle" of executing whrandom.pyc. |
| 52 # So the 2nd thread has a good chance of trying to look up 'randint' | |
| 53 # before the 1st thread has placed it in whrandom's dict. | |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
54 # |
| 1637 | 55 # 4) The more threads there are, the more likely that at least one of them |
| 56 # will do this before the 1st thread finishes the import work. | |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
57 # |
| 1637 | 58 # If that's right, a perhaps not-too-bad workaround would be to introduce a |
| 59 # static "you can't interrupt this thread" flag in ceval.c, check it before | |
| 60 # giving up interpreter_lock, and have IMPORT_NAME set it & restore (plain | |
| 61 # clearing would not work) it around its call to import_module. To its | |
| 62 # credit, there's something wonderfully perverse about fixing a race via an | |
| 63 # unprotected static <grin>. | |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
64 # |
| 1637 | 65 # as-with-most-other-things-(pseudo-)parallel-programming's-more-fun- |
| 66 # in-python-too!-ly y'rs - tim | |
|
16075
50bbe811b344
Whitespace normalization.
Tim Peters <tim.peters@gmail.com>
parents:
1637
diff
changeset
|
67 # |
| 1637 | 68 # Tim Peters tim@ksr.com |
| 69 # not speaking for Kendall Square Research Corp |