CODEWITHSUNDEEP
c++loggingboostboost-log
Ian Gralinski
Ian Gralinski

Reputation: 109

Is it safe to add or remove log sinks while still logging from other threads with boost log?

With boost::log is it safe to add or remove log sinks while still logging from other threads? Is there some manual locking that I need to do to make these operations thread-safe?

What I am trying to do is to start a new text file that contains a subset of entries of an existing log file between two points in my program.

For example if I have the following entries going to a log file "main_debug.log"

line 1
line 2
line 3
line 4

And then I add a new sink after line 1, and remove it after line 3, I would see "new_debug.log" containing the following entries

line 2
line 3

What I have seems to work most of the time, but I am occasionally seeing segmentation faults occurring within boost::log. An example of an instance of this occurring when I managed to catch it with gdb:

Program received signal SIGSEGV, Segmentation fault.
[Switching to LWP 8760]
boost::intrusive::list_impl<boost::intrusive::derivation_value_traits<boost::log::v2_mt_posix::attribute_value_set::node, boost::log::v2_mt_posix::attribute_value_set::implementation::node_traits, (boost::intrusive::link_mode_type)0>, unsigned int, true, void>::clear_and_dispose<boost::log::v2_mt_posix::attribute_value_set::implementation::disposer> (this=0x5e64aff4, disposer=...) at /boost-1.60.0/boost/intrusive/list.hpp:738
738     /boost-1.60.0/boost/intrusive/list.hpp: No such file or directory.
(gdb) bt
#0  boost::intrusive::list_impl<boost::intrusive::derivation_value_traits<boost::log::v2_mt_posix::attribute_value_set::node, boost::log::v2_mt_posix::attribute_value_set::implementation::node_traits, (boost::intrusive::link_mode_type)0>, unsigned int, true, void>::clear_and_dispose<boost::log::v2_mt_posix::attribute_value_set::implementation::disposer> (this=0x5e64aff4, disposer=...) at /boost-1.60.0/boost/intrusive/list.hpp:738
#1  boost::log::v2_mt_posix::attribute_value_set::implementation::~implementation (this=0x5e64afe8, __in_chrg=<optimized out>) at /boost-1.60.0/libs/log/src/attribute_value_set.cpp:150
#2  boost::log::v2_mt_posix::attribute_value_set::implementation::destroy (p=0x5e64afe8) at /boost-1.60.0/libs/log/src/attribute_value_set.cpp:239
#3  boost::log::v2_mt_posix::attribute_value_set::~attribute_value_set (this=0x5e64b3e4, __in_chrg=<optimized out>) at /boost-1.60.0/libs/log/src/attribute_value_set.cpp:519
#4  0x76e3bbac in boost::log::v2_mt_posix::record_view::public_data::~public_data (this=0x5e64b3e0, __in_chrg=<optimized out>) at /boost-1.60.0/boost/log/core/record_view.hpp:86
#5  boost::log::v2_mt_posix::record_view::private_data::~private_data (this=0x5e64b3e0, __in_chrg=<optimized out>) at /boost-1.60.0/libs/log/src/core.cpp:79
#6  boost::log::v2_mt_posix::record_view::private_data::destroy (this=0x5e64b3e0) at /boost-1.60.0/libs/log/src/core.cpp:131
#7  boost::log::v2_mt_posix::record_view::public_data::destroy (p=0x5e64b3e0) at /boost-1.60.0/libs/log/src/core.cpp:184
#8  0x0020b030 in boost::log::v2_mt_posix::sinks::asynchronous_sink<boost::log::v2_mt_posix::sinks::text_file_backend, boost::log::v2_mt_posix::sinks::unbounded_fifo_queue>::run() ()
#9  0x76d4be6c in boost::(anonymous namespace)::thread_proxy (param=<optimized out>) at /boost-1.60.0/libs/thread/src/pthread/thread.cpp:167
#10 0x76c22f00 in ?? () from /lib/libpthread.so.0

To add a new sink I am doing the following:

const auto pDebugBackend = boost::make_shared<boost::log::sinks::text_file_backend>(
    boost::log::keywords::file_name = "debug.log",
    boost::log::keywords::channel = "InfoConsole" );
const auto pNewDebugSink = boost::make_shared<boost::log::sinks::asynchronous_sink<boost::log::sinks::text_file_backend>>( pDebugBackend );

// Other code to set the filter and formatter for the sink.

boost::log::core::get()->add_sink( pNewDebugSink );

And to remove the sink some time later I have, which follows the order described in https://www.boost.org/doc/libs/1_60_0/libs/log/doc/html/log/detailed/sink_frontends.html#log.detailed.sink_frontends.async:

boost::log::core::get()->remove_sink( pNewDebugSink );
pNewDebugSink->stop();
pNewDebugSink->flush();
pNewDebugSink.reset();

I am using boost-1.60.0, and it is built with threading support enabled.

Upvotes: 0

Views: 536

Answers (1)

Andrey Semashev
Andrey Semashev

Reputation: 10614

With boost::log is it safe to add or remove log sinks while still logging from other threads?

Yes, although adding and removing sinks are two distinct operations, and you may miss some log records while the old sink is removed and the new one is not added yet.

Regarding the crashes you're seeing, it seems to happen while the dedicated logging thread is still running (i.e. before the stop method completes), so it is possible that removing the sink is not related. This may be a bug in Boost.Log or some other library used by it, but your Boost version is rather old. Try updating and if it still reproduces, report a bug in Boost.Log with a reproducer code sample.

Upvotes: 1

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