Serious performance and memory consumption hit if condition_variable methods condition notify_one or notify_all is used repeatedly

[Petr Dannhofer <petr.dannhofer@…>]

platform: Win32, MSVS11

condition_variable::generations member contains list of basic_cv_list_entry instances. As notify_one or notify_all is called, each instance member release is called, setting basic_cv_list_entry::notified member to true. There is no code which set basic_cv_list_entry::notified to false again, so the entry stays notified forever.

Items from condition_variable::generations are deleted only when there are no waiters for the entry. The waiters are removed in entry_manager::~entry_manager. New addition to 1.52 version is that waiter is removed only if the entry is not notified (line 198 thread/win32/condition_variable.hpp). As result, new entries are added for every get_wait_entry() call, which means for every wait call (as waiter can be added only to unnotified entry, which is the same story all over again), condition_variable::generations vector grows infinitely, consuming memory and processor time for useless searches for entries that could be removed.

[Petr Dannhofer <petr.dannhofer@…>]

proposed patch: remove if(! entry->is_notified()) condition from ~entry_manager()

[viboes]

Hi, I added this patch to solve #7461, but unfortunately it introduces a regression. I will rollback it and then take the time to analyze what is happening.

Thanks for the report.

[viboes]

Committed in trunk revision [81254].

[viboes]

Committed revision [81667].