Changes between Initial Version and Version 1 of Ticket #9145


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Timestamp:
Sep 21, 2013, 1:05:40 PM (9 years ago)
Author:
Chris Newbold
Comment:

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  • Ticket #9145 – Description

    initial v1  
    55I am occasionally seeing crashes deep inside the log record formatting machinery driven by the asynchronous_sink and have tracked the problem down to the combination of BOOST_LOG_FUNCTION and the unloading of dynamic libraries.
    66
    7 basic_named_scope_entry captures the function and file names using basic_string_literal, which just hangs on to the character pointer supplied during construction. BOOST_LOG_FUNCTION obtains function and file names using built-in constants such as __FILE__, which just flow through into the basic_named_scope_entries that comprise the current thread's context. These string constants (at least with MSVC on Windows) are stored in the dynamic library containing the code. So when a library is unloaded, the pointed-to strings are no longer valid.
     7basic_named_scope_entry captures the function and file names using basic_string_literal, which just hangs on to the character pointer supplied during construction. BOOST_LOG_FUNCTION obtains function and file names using built-in constants such as !__FILE!__, which just flow through into the basic_named_scope_entries that comprise the current thread's context. These string constants (at least with MSVC on Windows) are stored in the dynamic library containing the code. So when a library is unloaded, the pointed-to strings are no longer valid.
    88
    99Digging deeper, the implementation of named_scope_value::detach_from_thread() copies the scope list, but since this is just a container of basic_string_literals, only ends up copying the pointers to the literals and not the actual data. So FOO.DLL does some logging with BOOST_LOG_FUNCTION, log records get queued in the asynchronous_sink and then we unload FOO.DLL. Eventually the feeding thread in the asynchronous_sink gets to processing these records and crashes because the string literal pointers in the named scope list are now invalid.