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commit: dac5089eb7908e9fd643f46c913515082077281e |
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Author: Zac Medico <zmedico <AT> gentoo <DOT> org> |
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AuthorDate: Fri May 5 09:07:38 2017 +0000 |
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Commit: Brian Dolbec <dolsen <AT> gentoo <DOT> org> |
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CommitDate: Fri May 5 18:32:45 2017 +0000 |
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URL: https://gitweb.gentoo.org/proj/portage.git/commit/?id=dac5089e |
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|
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Eventloop: fix deadlock involving idle_add/call_soon (bug 617550) |
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|
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Guarantee that newly added idle_add/call_soon callbacks have an |
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opportunity to execute before the event loop decides to wait on |
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self._thread_condition without a timeout. This fixes a case where |
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the event loop would wait on self._thread_condition indefinitely, |
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even though a callback scheduled by the AsynchronousTask._async_wait |
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method needed to be executed first. |
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|
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X-Gentoo-bug: 617550 |
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X-Gentoo-bug-url: https://bugs.gentoo.org/show_bug.cgi?id=617550 |
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Acked-by: Brian Dolbec <dolsen <AT> gentoo.org> |
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|
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pym/portage/util/_eventloop/EventLoop.py | 18 ++++++++++++++++-- |
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1 file changed, 16 insertions(+), 2 deletions(-) |
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|
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diff --git a/pym/portage/util/_eventloop/EventLoop.py b/pym/portage/util/_eventloop/EventLoop.py |
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index 712838e3d..cd154005f 100644 |
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--- a/pym/portage/util/_eventloop/EventLoop.py |
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+++ b/pym/portage/util/_eventloop/EventLoop.py |
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@@ -108,6 +108,15 @@ class EventLoop(object): |
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self._poll_event_handler_ids = {} |
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# Increment id for each new handler. |
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self._event_handler_id = 0 |
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+ # New call_soon callbacks must have an opportunity to |
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+ # execute before it's safe to wait on self._thread_condition |
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+ # without a timeout, since delaying its execution indefinitely |
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+ # could lead to a deadlock. The following attribute stores the |
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+ # event handler id of the most recently added call_soon callback. |
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+ # If this attribute has changed since the last time that the |
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+ # call_soon callbacks have been called, then it's not safe to |
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+ # wait on self._thread_condition without a timeout. |
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+ self._call_soon_id = 0 |
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# Use OrderedDict in order to emulate the FIFO queue behavior |
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# of the AbstractEventLoop.call_soon method. |
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self._idle_callbacks = OrderedDict() |
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@@ -250,10 +259,15 @@ class EventLoop(object): |
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|
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if not event_handlers: |
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with self._thread_condition: |
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+ prev_call_soon_id = self._call_soon_id |
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if self._run_timeouts(): |
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events_handled += 1 |
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timeouts_checked = True |
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- if not event_handlers and not events_handled and may_block: |
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+ |
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+ call_soon = prev_call_soon_id != self._call_soon_id |
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+ |
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+ if (not call_soon and not event_handlers |
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+ and not events_handled and may_block): |
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# Block so that we don't waste cpu time by looping too |
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# quickly. This makes EventLoop useful for code that needs |
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# to wait for timeout callbacks regardless of whether or |
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@@ -457,7 +471,7 @@ class EventLoop(object): |
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@return: an integer ID |
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""" |
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with self._thread_condition: |
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- source_id = self._new_source_id() |
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+ source_id = self._call_soon_id = self._new_source_id() |
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self._idle_callbacks[source_id] = self._idle_callback_class( |
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args=args, callback=callback, source_id=source_id) |
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self._thread_condition.notify() |
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