Reported by valgrind using the command below:
$ valgrind jackd -p128 -t2000 -dalsa -dhw:0 -r44100 -p2048 -n2 -S
==17496== Memcheck, a memory error detector
==17496== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==17496== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==17496== Command: jackd -p128 -t2000 -dalsa -dhw:0 -r44100 -p2048 -n2 -S
==17496==
jackdmp 1.9.11
Copyright 2001-2005 Paul Davis and others.
Copyright 2004-2016 Grame.
jackdmp comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
JACK server starting in realtime mode with priority 10
self-connect-mode is "Don't restrict self connect requests"
creating alsa driver ... hw:0|hw:0|2048|2|44100|0|0|nomon|swmeter|-|16bit
configuring for 44100Hz, period = 2048 frames (46.4 ms), buffer = 2 periods
ALSA: final selected sample format for capture: 16bit little-endian
ALSA: use 2 periods for capture
ALSA: final selected sample format for playback: 16bit little-endian
ALSA: use 2 periods for playback
==17496== Thread 3:
==17496== Conditional jump or move depends on uninitialised value(s)
==17496==    at 0x4E91CC9: Jack::JackEngineControl::CalcCPULoad(Jack::JackClientInterface**, Jack::JackGraphManager*, unsigned long, unsigned long) (JackEngineControl.cpp:58)
==17496==    by 0x4EB3256: Jack::JackEngineControl::CycleBegin(Jack::JackClientInterface**, Jack::JackGraphManager*, unsigned long, unsigned long) (JackEngineControl.h:153)
==17496==    by 0x4EAF54A: Jack::JackEngine::Process(unsigned long, unsigned long) (JackEngine.cpp:166)
==17496==    by 0x4EA922E: Jack::JackLockedEngine::Process(unsigned long, unsigned long) (JackLockedEngine.h:261)
==17496==    by 0x4EA8819: Jack::JackAudioDriver::ProcessGraphAsyncMaster() (JackAudioDriver.cpp:250)
==17496==    by 0x4EA87D0: Jack::JackAudioDriver::ProcessGraphAsync() (JackAudioDriver.cpp:236)
==17496==    by 0x4EA8795: Jack::JackAudioDriver::ProcessAsync() (JackAudioDriver.cpp:225)
==17496==    by 0x4EA870E: Jack::JackAudioDriver::Process() (JackAudioDriver.cpp:202)
==17496==    by 0x4EBA5DA: Jack::JackThreadedDriver::Process() (JackThreadedDriver.cpp:71)
==17496==    by 0x4EBAC52: Jack::JackThreadedDriver::Execute() (JackThreadedDriver.cpp:244)
==17496==    by 0x4EA4B63: Jack::JackPosixThread::ThreadHandler(void*) (JackPosixThread.cpp:61)
==17496==    by 0x59F5181: start_thread (pthread_create.c:312)
==17496==
^CJack main caught signal 2
==17496==
==17496== HEAP SUMMARY:
==17496==     in use at exit: 95,475 bytes in 1,441 blocks
==17496==   total heap usage: 2,793 allocs, 1,352 frees, 7,217,645 bytes allocated
==17496==
==17496== LEAK SUMMARY:
==17496==    definitely lost: 1,458 bytes in 10 blocks
==17496==    indirectly lost: 7,680 bytes in 4 blocks
==17496==      possibly lost: 42,998 bytes in 1,314 blocks
==17496==    still reachable: 43,339 bytes in 113 blocks
==17496==         suppressed: 0 bytes in 0 blocks
==17496== Rerun with --leak-check=full to see details of leaked memory
==17496==
==17496== For counts of detected and suppressed errors, rerun with: -v
==17496== Use --track-origins=yes to see where uninitialised values come from
==17496== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)