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Diffstat (limited to 'Doc/library/threading.rst')
| -rw-r--r-- | Doc/library/threading.rst | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst index 6f3e95b..3f62e69 100644 --- a/Doc/library/threading.rst +++ b/Doc/library/threading.rst @@ -724,3 +724,26 @@ Currently, :class:`Lock`, :class:`RLock`, :class:`Condition`, with some_rlock: print("some_rlock is locked while this executes") + +.. _threaded-imports: + +Importing in threaded code +-------------------------- + +While the import machinery is thread safe, there are two key +restrictions on threaded imports due to inherent limitations in the way +that thread safety is provided: + +* Firstly, other than in the main module, an import should not have the + side effect of spawning a new thread and then waiting for that thread in + any way. Failing to abide by this restriction can lead to a deadlock if + the spawned thread directly or indirectly attempts to import a module. +* Secondly, all import attempts must be completed before the interpreter + starts shutting itself down. This can be most easily achieved by only + performing imports from non-daemon threads created through the threading + module. Daemon threads and threads created directly with the thread + module will require some other form of synchronization to ensure they do + not attempt imports after system shutdown has commenced. Failure to + abide by this restriction will lead to intermittent exceptions and + crashes during interpreter shutdown (as the late imports attempt to + access machinery which is no longer in a valid state). |