fix memory leak in SIOReader

[gaede]

BEGINRELEASENOTES

• fix memory leak in SIOReader
  • delete previous Event and RunHeader before reading a new one
  • this restores the old expected behavior of the IO::LCReader
  • for parallel event reading one needs to use the MT::LCReader directly and
    handle the memory accordingly (e.g. via use of std::unique_ptr)
    - see $LCIO/src/cpp/src/EXAMPLE/lcio_parallel_processing.cc
• fixes memory issue using pyLCIO in latest version? #97 and Memory leak for lcio_reader->readNextEvent() #98

ENDRELEASENOTES

[jstrube]

That fixes the memory leak, but now it's not thread safe. Not sure if it was before, I haven't had a chance to test, yet.

[gaede]

The SIOReader implementing the IO:LCReader interface cannot be thread-safe and handle the memory for the user at the same time.
For parallel processing one needs to use the MT::LCReader directly and handle the event memory in the user code ( see the release notes of #99)...

[Romendakil]

Apparently exactly this commit breaks the LCIO Interface of WHIZARD. Trying to delete the _currentEvent leads to a crash. Not sure whether the commit is wrong, or this is an error in our interface since the beginning.

[jstrube]

Hmm, I don't observe a crash, but the commit surely doesn't guard against double deletes. The if statements are redundant (a delete on a nullptr is a no-op, see also https://stackoverflow.com/questions/6731331/is-it-still-safe-to-delete-nullptr-in-c0x). To guard against double deletes, one could set the pointer to nullptr after the delete. If I understand correctly, the segfault is only after reading the last event?
Maybe the destructor calls a delete on an already deleted event? Is that consistent with your error message?

[Romendakil]

Actually, it crashes whenever we try to read the first event, not the last one. You are right, the if-clause around the delete is unnecessary. I'm note sure it really is a double delete. Maybe the crash is because this pointer comes out of an external code. The error message is:

*** Break *** segmentation violation



===========================================================
There was a crash.
This is the entire stack trace of all threads:
===========================================================
#0  0x00007fa74103e6e7 in __GI___waitpid (pid=4737, stat_loc=stat_loc
entry=0x7fffbdeb7fe8, options=options
entry=0) at ../sysdeps/unix/sysv/linux/waitpid.c:30
#1  0x00007fa740fa9107 in do_system (line=<optimized out>) at ../sysdeps/posix/system.c:149
#2  0x00007fa73f026643 in TUnixSystem::StackTrace() () from /home/reuter/local/lib/libCore.so
#3  0x00007fa73f029034 in TUnixSystem::DispatchSignals(ESignals) () from /home/reuter/local/lib/libCore.so
#4  <signal handler called>
#5  0x00007fa741b23115 in SIO::SIOReader::readNextEvent (this=0x563b56417ed0, accessMode=0) at /home/reuter/local/packages/LCIO-02-15-03/src/cpp/src/SIO/SIOReader.cc:108
#6  0x00007fa744307f56 in read_lcio_event (lcRdr=0x563b56417ed0) at ../../../src/lcio/LCIOWrap.cpp:123
#7  0x00007fa743f7a669 in lcio_interface_MP_lcio_read_event (lcrdr_=0x7fa73c576f50, evt_=0x7fa73c576f60, ok_=0x7fffbdebab58) at lcio_interface.f90:937
#8  0x00007fa743fa2e85 in eio_lcio_MP_eio_lcio_input_i_prc (eio_=0x7fa73c576d50, eio_Sig=0x7fa7446d0288 <eio_lcio_DT_eio_lcio_tHEADER+8>, eio_Dtp=0x0, i_prc_=0x7fffbdebabc0, iostat_=0x7fffbdebabbc) at eio_lcio.f90:305
#9  0x0000563b555728dc in eio_lcio_uti_MP_eio_lcio_2 (u_=0x7fffbdebae80) at eio_lcio_uti.f90:265
#10 0x00007fa7442e932a in unit_tests_MP_test (test_proc_=0x563b555705e4 <eio_lcio_uti_MP_eio_lcio_2>, name_=0x563b557d55e4 "eio_lcio_2", description_=0x563b557d55d0 "read event contents", u_log_=0x7fffbdebaee4, results_=0x563b55a07fd0 <test_results_>, name_Len=10, description_Len=19) at unit_tests.f90:196
#11 0x0000563b55570553 in eio_lcio_ut_MP_eio_lcio_test (u_=0x7fffbdebaee4, results_=0x563b55a07fd0 <test_results_>) at eio_lcio_ut.f90:46
#12 0x0000563b54d9f35e in main_ut_IP_whizard_check (check_=0x563b55a08000 <check_>, results_=0x563b55a07fd0 <test_results_>) at main_ut.f90:676
#13 0x0000563b54d9c221 in main_ut_ (__NAGf90_main_args=0x0) at main_ut.f90:306
#14 0x0000563b54d9a488 in main (argc=4, argv=0x7fffbdebbce8) at main_ut.f90:29
===========================================================


The lines below might hint at the cause of the crash.
You may get help by asking at the ROOT forum http://root.cern.ch/forum
Only if you are really convinced it is a bug in ROOT then please submit a
report at http://root.cern.ch/bugs Please post the ENTIRE stack trace
from above as an attachment in addition to anything else
that might help us fixing this issue.
===========================================================
#5  0x00007fa741b23115 in SIO::SIOReader::readNextEvent (this=0x563b56417ed0, accessMode=0) at /home/reuter/local/packages/LCIO-02-15-03/src/cpp/src/SIO/SIOReader.cc:108
#6  0x00007fa744307f56 in read_lcio_event (lcRdr=0x563b56417ed0) at ../../../src/lcio/LCIOWrap.cpp:123
#7  0x00007fa743f7a669 in lcio_interface_MP_lcio_read_event (lcrdr_=0x7fa73c576f50, evt_=0x7fa73c576f60, ok_=0x7fffbdebab58) at lcio_interface.f90:937
#8  0x00007fa743fa2e85 in eio_lcio_MP_eio_lcio_input_i_prc (eio_=0x7fa73c576d50, eio_Sig=0x7fa7446d0288 <eio_lcio_DT_eio_lcio_tHEADER+8>, eio_Dtp=0x0, i_prc_=0x7fffbdebabc0, iostat_=0x7fffbdebabbc) at eio_lcio.f90:305
#9  0x0000563b555728dc in eio_lcio_uti_MP_eio_lcio_2 (u_=0x7fffbdebae80) at eio_lcio_uti.f90:265
#10 0x00007fa7442e932a in unit_tests_MP_test (test_proc_=0x563b555705e4 <eio_lcio_uti_MP_eio_lcio_2>, name_=0x563b557d55e4 "eio_lcio_2", description_=0x563b557d55d0 "read event contents", u_log_=0x7fffbdebaee4, results_=0x563b55a07fd0 <test_results_>, name_Len=10, description_Len=19) at unit_tests.f90:196
#11 0x0000563b55570553 in eio_lcio_ut_MP_eio_lcio_test (u_=0x7fffbdebaee4, results_=0x563b55a07fd0 <test_results_>) at eio_lcio_ut.f90:46
#12 0x0000563b54d9f35e in main_ut_IP_whizard_check (check_=0x563b55a08000 <check_>, results_=0x563b55a07fd0 <test_results_>) at main_ut.f90:676
#13 0x0000563b54d9c221 in main_ut_ (__NAGf90_main_args=0x0) at main_ut.f90:306
#14 0x0000563b54d9a488 in main (argc=4, argv=0x7fffbdebbce8) at main_ut.f90:29
===========================================================

[jstrube]

That message is a bit weird. Line 108, the one with the error is the return. The delete happens in line 104. Is this code identical to tag 02-15-03?
Not sure how a return can segfault.

[Romendakil]

I just inserted some debug lines, in the original LCIO 02-15-03 it is line 104. BTW, I opened a new issue.

[Romendakil]

If I keep the delete statement, our code also works if I replace:
_currentEvent = _reader.readNextEvent( accessMode ).release() ;
by
EVENT::LCEvent* _currentEvent = _reader.readNextEvent( accessMode ).release() ;

[jstrube]

Not sure why that would work. You are just shadowing the member variable with a local variable with the same name.

I can't say I understand exactly what's going on, but reading this: https://en.cppreference.com/w/cpp/memory/unique_ptr, I get

The object is disposed of, using the associated deleter when either of the following happens:
the managing unique_ptr object is destroyed
the managing unique_ptr object is assigned another pointer via operator= or reset().

If that's the case, then the delete destroys the object, and then the assignment calls the destructor again?
edit/ never mind. _currentEvent is not a unique_ptr, so I misunderstood how that worked.