pthread key leak

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
25/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
cpp, linux
Domain
operating-systems

Research direction

Start with libs/thread/src/pthread/thread.cpp, especially create_current_thread_tls_key(), and reproduce the repeated shared-library load/unload case from boost_pthread_key_leak.zip. Read commit 47357de276fe4fc01469f34c1dbf8b26fdbc1c4b and ticket #12049 to understand the existing race-related behavior. Done means resolving the pthread key leak without reintroducing the reported issue.

Written by the indexing model from the issue text.

Description

I am using boost::thread statically linkes in a shared library and found a pthread key leak. When I repeat loading and unloading the library, pthread keys are leaking and after some time, I get

main: boost_1_77_0/libs/thread/src/pthread/thread.cpp:148: void boost::detail::{anonymous}::create_current_thread_tls_key(): Assertion `!pthread_key_create(&current_thread_tls_key,&tls_destructor)' failed.

The leaking pthread key is allocated in libs/thread/src/pthread/thread.cpp. The code for de-allocating the pthread key is #ifdef'ed with BOOST_THREAD_PATCH. Without BOOST_THREAD_PATCH, the binary only calls to pthread_key_create, but no call to pthread_key_delete:

The problem seems to be solved, if I #define BOOST_THREAD_PATCH. But this #ifdef was added in 47357de276fe4fc01469f34c1dbf8b26fdbc1c4b to solve bug #12049. (https://www.boost.org/doc/libs/1_64_0/doc/html/thread/changes.html) (https://svn.boost.org/trac10/ticket/12049)

Unfortunately, I do not really understand the problem in ticket #12049. To me, it looks like a race condition and the leaking pthread key just prevents any harm caused by the race condition. That doesn't really look like a fix to me, just solves one problem by creating a new one. :-(

Here is my source code: boost_pthread_key_leak.zip

I am using linux on x86_64, c++ (Gentoo 10.3.0-r2 p3) 10.3.0

Dominant language
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