Segfault in AsyncMySQLClient

### HHVM Version

```raw
$ hhvm --version
HipHop VM 3.30.3 (rel)
Compiler: remotes/origin/3.30.3-slack-0-g5a3df294bf9d921093eac96d93aff8f57b0779e9
Repo schema: fb5f31ec9856182de174e17a7439c92f221ad9a7
```

```raw
$ hh_client --version
hh--3.30.3 Mon Apr 1 17:25:31 2019
```

### Operating System and Version

Several machines, all Ubuntu 16.04:
```raw
Linux 4.4.0-1075-aws #85-Ubuntu SMP Thu Jan 17 17:15:12 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
```

### Standalone code, or other way to reproduce the problem

No known repro - this happens on about 1.5% of our hosts every day, running HHVM in the following way:

- HHVM run in CLI mode from `runsv`
- Main script uses local xbox server to run multiple jobs at once

### Actual result

HHVM segfaults. On a sample of 10 hosts that encountered this issue, the only thing in common was the following trace (obtained in `gdb` from the dumped core):
```raw
#0 0x00007fe879866269 in raise (sig=11) at ../sysdeps/unix/sysv/linux/pt-raise.c:35
#1 0x0000000001415c20 in HPHP::bt_handler(int, siginfo_t*, void*) ()
#2
#3 0x0000000003540083 in facebook::common::mysql_client::AsyncConnectionPool::ConnStorage::cleanupConnections() ()
#4 0x0000000003540558 in facebook::common::mysql_client::AsyncConnectionPool::CleanUpTimer::timeoutExpired() ()
#5 0x0000000003750532 in folly::AsyncTimeout::libeventCallback(int, short, void*) ()
#6 0x00007fe87a7574c9 in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#7 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#8 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#9 0x0000000003556bf0 in std::thread::_Impl >::_M_run() ()
#10 0x00007fe873de3c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#11 0x00007fe87985c6ba in start_thread (arg=) at pthread_create.c:333
#12 0x00007fe87354941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
```

*Note: See end of this issue description for 3 example outputs of `thread apply all bt`.*

### Expected result

HHVM does not segfault.

### 3 Example Outputs of `thread apply all bt`

#### Example 1

```raw
Thread 12 (Thread 0x7f5b5a9cf700 (LWP 9689)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b5a9cf700) at pthread_create.c:333
#6 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 11 (Thread 0x7f5b78bff700 (LWP 19695)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b78bff700) at pthread_create.c:333
#6 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 10 (Thread 0x7f5b88f0e700 (LWP 19657)):
#0 0x00007f5b94d7c74d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000000001aa44a6 in std::thread::_Impl >::_M_run() ()
#2 0x00007f5b95622c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b88f0e700) at pthread_create.c:333
#4 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 9 (Thread 0x7f5b6bbff700 (LWP 19699)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b6bbff700) at pthread_create.c:333
#6 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 8 (Thread 0x7f5b683ff700 (LWP 19700)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b683ff700) at pthread_create.c:333
#6 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 7 (Thread 0x7f5b713ff700 (LWP 19698)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b713ff700) at pthread_create.c:333
#6 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 6 (Thread 0x7f5b5c72f700 (LWP 465)):
#0 0x00007f5b94d88a13 in epoll_wait () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007f5b9bfabb18 in ?? () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#2 0x00007f5b9bf95e2d in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#3 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#4 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#5 0x00007f5b95622c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#6 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b5c72f700) at pthread_create.c:333
#7 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 5 (Thread 0x7f5b747fe700 (LWP 19697)):
#0 0x00007f5b94d88a13 in epoll_wait () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007f5b9bfabb18 in ?? () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#2 0x00007f5b9bf95e2d in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#3 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#4 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#5 0x0000000003556bf0 in std::thread::_Impl >::_M_run() ()
#6 0x00007f5b95622c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#7 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b747fe700) at pthread_create.c:333
#8 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 4 (Thread 0x7f5b80fff700 (LWP 19693)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b80fff700) at pthread_create.c:333
#6 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 3 (Thread 0x7f5b7cbff700 (LWP 19694)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b7cbff700) at pthread_create.c:333
#6 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 2 (Thread 0x7f5b9d4c1340 (LWP 19653)):
#0 0x00007f5b94d7c74d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x00000000015ce939 in HPHP::Socket::readImpl(char*, long) ()
#2 0x00000000015d5a55 in HPHP::SSLSocket::readImpl(char*, long) ()
#3 0x00000000014692e4 in HPHP::File::readLine(long) ()
#4 0x0000000003386a0d in HPHP::f_fgets(HPHP::Resource const&, long) ()
#5 0x0000000007475122 in ?? ()
#6 0x000000000740006f in ?? ()
#7 0x00007ffe7b4075f0 in ?? ()
#8 0x00007ffe7b407500 in ?? ()
#9 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Thread 1 (Thread 0x7f5b74fff700 (LWP 19696)):
#0 0x00007f5b9b0a5269 in raise (sig=11) at ../sysdeps/unix/sysv/linux/pt-raise.c:35
#1 0x0000000001415c20 in HPHP::bt_handler(int, siginfo_t*, void*) ()
#2
#3 0x0000000003540083 in facebook::common::mysql_client::AsyncConnectionPool::ConnStorage::cleanupConnections() ()
#4 0x0000000003540558 in facebook::common::mysql_client::AsyncConnectionPool::CleanUpTimer::timeoutExpired() ()
#5 0x0000000003750532 in folly::AsyncTimeout::libeventCallback(int, short, void*) ()
#6 0x00007f5b9bf964c9 in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#7 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#8 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#9 0x0000000003556bf0 in std::thread::_Impl >::_M_run() ()
#10 0x00007f5b95622c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#11 0x00007f5b9b09b6ba in start_thread (arg=0x7f5b74fff700) at pthread_create.c:333
#12 0x00007f5b94d8841d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
```

#### Example 2

```raw
Thread 13 (Thread 0x7ff9c9646700 (LWP 32221)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007ffa2095c6ba in start_thread (arg=0x7ff9c9646700) at pthread_create.c:333
#6 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 12 (Thread 0x7ffa0e70e700 (LWP 26222)):
#0 0x00007ffa1a63d74d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000000001aa44a6 in std::thread::_Impl >::_M_run() ()
#2 0x00007ffa1aee3c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3 0x00007ffa2095c6ba in start_thread (arg=0x7ffa0e70e700) at pthread_create.c:333
#4 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 11 (Thread 0x7ff9e93ff700 (LWP 29423)):
#0 0x00007ffa1a649a13 in epoll_wait () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007ffa2186cb18 in ?? () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#2 0x00007ffa21856e2d in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#3 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#4 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#5 0x00007ffa1aee3c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#6 0x00007ffa2095c6ba in start_thread (arg=0x7ff9e93ff700) at pthread_create.c:333
#7 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 10 (Thread 0x7ff98f484700 (LWP 14957)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007ffa2095c6ba in start_thread (arg=0x7ff98f484700) at pthread_create.c:333
#6 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 9 (Thread 0x7ff98bc04700 (LWP 14960)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007ffa2095c6ba in start_thread (arg=0x7ff98bc04700) at pthread_create.c:333
#6 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 8 (Thread 0x7ff9f2bff700 (LWP 26230)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007ffa2095c6ba in start_thread (arg=0x7ff9f2bff700) at pthread_create.c:333
#6 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 7 (Thread 0x7ff9fa3fe700 (LWP 26228)):
#0 0x00007ffa1a649a13 in epoll_wait () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007ffa2186cb18 in ?? () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#2 0x00007ffa21856e2d in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#3 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#4 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#5 0x0000000003556bf0 in std::thread::_Impl >::_M_run() ()
#6 0x00007ffa1aee3c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#7 0x00007ffa2095c6ba in start_thread (arg=0x7ff9fa3fe700) at pthread_create.c:333
#8 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 6 (Thread 0x7ff9fe7ff700 (LWP 26226)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007ffa2095c6ba in start_thread (arg=0x7ff9fe7ff700) at pthread_create.c:333
#6 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 5 (Thread 0x7ff9f93ff700 (LWP 26229)):
#0 pthread_cond_timedwait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_timedwait.S:225
#1 0x0000000002ab698c in HPHP::AsioExternalThreadEventQueue::receiveSomeUntil(std::chrono::time_point > >) ()
#2 0x0000000002ab4435 in HPHP::AsioContext::runUntil(HPHP::c_WaitableWaitHandle*) ()
#3 0x0000000002acd16e in HPHP::c_WaitableWaitHandle::join() ()
#4 0x0000000002ac5369 in HPHP::f_join(HPHP::Object const&) ()
#5 0x00000000070c3f10 in ?? ()
#6 0x000000000700006f in ?? ()
#7 0x00007ff9f93fc770 in ?? ()
#8 0x00007ff9f93fc680 in ?? ()
#9 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
#10 0x000000000727bcce in ?? ()
#11 0x00007ffa1031ea00 in ?? ()
#12 0x000000010000007b in ?? ()
#13 0x0000000000000000 in ?? ()

Thread 4 (Thread 0x7ffa05fff700 (LWP 26224)):
#0 0x00007ffa1a63d74d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007ffa21409a63 in ?? () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#2 0x00007ffa214046f3 in curl_multi_wait () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#3 0x00007ffa213fd547 in curl_easy_perform () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#4 0x0000000002b56bb4 in HPHP::CurlResource::execute() ()
#5 0x0000000002b59eb3 in HPHP::f_curl_exec(HPHP::Resource const&) ()
#6 0x0000000007149aa2 in ?? ()
#7 0x000000000700006f in ?? ()
#8 0x00007ffa05ffc490 in ?? ()
#9 0x00007ffa05ffc3a0 in ?? ()
#10 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
#11 0x0000000007515d67 in ?? ()
#12 0x00007ffa1034c800 in ?? ()
#13 0x00000001000003e7 in ?? ()
#14 0x0000000000002751 in ?? ()
#15 0x0000000000000000 in ?? ()

Thread 3 (Thread 0x7ffa22d82340 (LWP 26218)):
#0 0x00007ffa1a60e30d in nanosleep () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007ffa1a63fd94 in usleep (useconds=) at ../sysdeps/posix/usleep.c:32
#2 0x00000000033a34c3 in HPHP::f_usleep(int) ()
#3 0x000000000725201d in ?? ()
#4 0x000000000700006f in ?? ()
#5 0xffffffffffffefe8 in ?? ()
#6 0x00007ffff1745e50 in ?? ()
#7 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Thread 2 (Thread 0x7ffa023ff700 (LWP 26225)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007ffa2095c6ba in start_thread (arg=0x7ffa023ff700) at pthread_create.c:333
#6 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 1 (Thread 0x7ff9fabff700 (LWP 26227)):
#0 0x00007ffa20966269 in raise (sig=11) at ../sysdeps/unix/sysv/linux/pt-raise.c:35
#1 0x0000000001415c20 in HPHP::bt_handler(int, siginfo_t*, void*) ()
#2
#3 0x0000000003540083 in facebook::common::mysql_client::AsyncConnectionPool::ConnStorage::cleanupConnections() ()
#4 0x0000000003540558 in facebook::common::mysql_client::AsyncConnectionPool::CleanUpTimer::timeoutExpired() ()
#5 0x0000000003750532 in folly::AsyncTimeout::libeventCallback(int, short, void*) ()
#6 0x00007ffa218574c9 in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#7 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#8 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#9 0x0000000003556bf0 in std::thread::_Impl >::_M_run() ()
#10 0x00007ffa1aee3c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#11 0x00007ffa2095c6ba in start_thread (arg=0x7ff9fabff700) at pthread_create.c:333
#12 0x00007ffa1a64941d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
```

#### Example 3 (this one is super weird)

```raw
Thread 22 (Thread 0x7f8b833ff700 (LWP 17521)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8b833ff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 21 (Thread 0x7f8bcb7fe700 (LWP 20187)):
#0 0x00007f8bebfb1a13 in epoll_wait () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007f8bf31d4b18 in ?? () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#2 0x00007f8bf31bee2d in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#3 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#4 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#5 0x0000000003556bf0 in std::thread::_Impl >::_M_run() ()
#6 0x00007f8bec84bc80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#7 0x00007f8bf22c46ba in start_thread (arg=0x7f8bcb7fe700) at pthread_create.c:333
#8 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 20 (Thread 0x7f8bd47ff700 (LWP 20184)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8bd47ff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 19 (Thread 0x7f8bbb3ff700 (LWP 20206)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8bbb3ff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 18 (Thread 0x7f8bbebff700 (LWP 20190)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8bbebff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 17 (Thread 0x7f8bcfbff700 (LWP 20185)):
#0 0x00007f8bebfa574d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007f8bf2d71a63 in ?? () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#2 0x00007f8bf2d6c6f3 in curl_multi_wait () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#3 0x00007f8bf2d65547 in curl_easy_perform () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#4 0x0000000002b56bb4 in HPHP::CurlResource::execute() ()
#5 0x0000000002b59eb3 in HPHP::f_curl_exec(HPHP::Resource const&) ()
#6 0x0000000005d150e7 in ?? ()
#7 0x0000000005c0006f in ?? ()
#8 0x00007f8bcfbfc770 in ?? ()
#9 0x00007f8bcfbfc680 in ?? ()
#10 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
#11 0x0000000005ddc615 in ?? ()
#12 0x00007f8be1b4c800 in ?? ()
#13 0x00000001000000be in ?? ()
#14 0x00007f8bda5464e0 in ?? ()
#15 0x0000000000000000 in ?? ()

Thread 16 (Thread 0x7f8bf46ea340 (LWP 20170)):
#0 0x00007f8bebfa574d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x00000000015ce939 in HPHP::Socket::readImpl(char*, long) ()
#2 0x00000000015d5a55 in HPHP::SSLSocket::readImpl(char*, long) ()
#3 0x00000000014692e4 in HPHP::File::readLine(long) ()
#4 0x0000000003386a0d in HPHP::f_fgets(HPHP::Resource const&, long) ()
#5 0x0000000005c74122 in ?? ()
#6 0x0000000005c0006f in ?? ()
#7 0x00007fffe670a900 in ?? ()
#8 0x00007fffe670a810 in ?? ()
#9 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Thread 15 (Thread 0x7f8b78bff700 (LWP 17526)):
#0 0x00000000012739c4 in HPHP::APCArray::Delete(HPHP::APCHandle*) ()
#1 0x00000000012738e1 in HPHP::APCArray::Delete(HPHP::APCHandle*) ()
#2 0x00000000013e6245 in HPHP::ConcurrentTableSharedStore::storeImpl(HPHP::String const&, HPHP::Variant const&, long, bool, bool) ()
#3 0x0000000002a6c8e4 in HPHP::f_apc_store(HPHP::Variant const&, HPHP::Variant const&, long) ()
#4 0x0000000005c05e85 in ?? ()
#5 0x0000000005c0006f in ?? ()
#6 0x00007f8b78bfc770 in ?? ()
#7 0x00007f8b78bfc680 in ?? ()
#8 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
#9 0x0000000005c05e05 in ?? ()
#10 0x00007f8be1ac2b60 in ?? ()
#11 0x0000000300000047 in ?? ()
#12 0x00007f8bc68072d0 in ?? ()
#13 0x0000000000000000 in ?? ()

Thread 14 (Thread 0x7f8b7c3ff700 (LWP 17525)):
#0 0x00007f8bebfa574d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007f8bf2d71a63 in ?? () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#2 0x00007f8bf2d6c6f3 in curl_multi_wait () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#3 0x00007f8bf2d65547 in curl_easy_perform () from /usr/lib/x86_64-linux-gnu/libcurl.so.4
#4 0x0000000002b56bb4 in HPHP::CurlResource::execute() ()
#5 0x0000000002b59eb3 in HPHP::f_curl_exec(HPHP::Resource const&) ()
#6 0x0000000005d150e7 in ?? ()
#7 0x0000000005c0006f in ?? ()
#8 0x00007f8b7c3fc770 in ?? ()
#9 0x00007f8b7c3fc680 in ?? ()
#10 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
#11 0x0000000005ddc615 in ?? ()
#12 0x00007f8be1b4c800 in ?? ()
#13 0x00000001000000be in ?? ()
#14 0x00007f8bda5464e0 in ?? ()
#15 0x0000000000000000 in ?? ()

Thread 13 (Thread 0x7f8b753ff700 (LWP 17527)):
#0 0x00007f8bf1a40a88 in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.1.0.0
#1 0x00007f8bf207a100 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#2 0x00007f8bf207a158 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#3 0x00007f8bf207a1b0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#4 0x00007f8bf207a208 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#5 0x00007f8bf207a2b8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#6 0x00007f8bf207a310 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#7 0x00007f8bf207a368 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#8 0x00007f8bf207a3c0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#9 0x00007f8bf207a418 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#10 0x00007f8bf207a520 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#11 0x00007f8bf207a578 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#12 0x00007f8bf207a5d0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#13 0x00007f8bf207a628 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#14 0x00007f8bf207a680 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#15 0x00007f8bf207a6d8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#16 0x00007f8bf207a730 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#17 0x00007f8bf207a788 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#18 0x00007f8bf207a7e0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#19 0x00007f8bf207a838 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#20 0x00007f8bf207a8e8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#21 0x00007f8bf207a940 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#22 0x00007f8bf207a998 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#23 0x00007f8bf207a9f0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#24 0x00007f8bf207aa48 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#25 0x00007f8bf207acb0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#26 0x00007f8bf207ad08 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#27 0x00007f8bf207ad60 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#28 0x00007f8bf207adb8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#29 0x00007f8bf207ae10 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#30 0x00007f8bf207aec0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#31 0x00007f8bf207af18 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#32 0x00007f8bf207af70 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#33 0x00007f8bf207afc8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#34 0x00007f8bf207b020 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#35 0x00007f8bf207b078 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#36 0x00007f8bf207b0d0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#37 0x00007f8bf207b128 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#38 0x00007f8bf207b180 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#39 0x00007f8bf207b230 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#40 0x00007f8bf207b288 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#41 0x00007f8bf207b2e0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#42 0x00007f8bf207b338 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#43 0x00007f8bf207b390 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#44 0x00007f8bf207b3e8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#45 0x00007f8bf207b440 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#46 0x00007f8bf207b498 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#47 0x00007f8bf207b4f0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#48 0x00007f8bf207b548 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#49 0x00007f8bf207b6a8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#50 0x00007f8bf207b700 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#51 0x00007f8bf207b758 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#52 0x00007f8bf207b7b0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#53 0x00007f8bf207b860 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#54 0x00007f8bf207b8b8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#55 0x00007f8bf207b910 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#56 0x00007f8bf207b968 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#57 0x00007f8bf207ba18 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#58 0x00007f8bf207ba70 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#59 0x00007f8bf207bac8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#60 0x00007f8bf207bb20 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#61 0x00007f8bf207bbd0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#62 0x00007f8bf207bc28 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#63 0x00007f8bf207bc80 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#64 0x00007f8bf207bcd8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#65 0x00007f8bf207bee8 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#66 0x00007f8bf207bf40 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#67 0x00007f8bf207bf98 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#68 0x00007f8bf207bff0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#69 0x00007f8bf207c048 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.0.0
#70 0x000000000377a327 in folly::ssl::detail::callbackLocking(int, int, char const*, int) ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

Thread 12 (Thread 0x7f8b98fff700 (LWP 26593)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8b98fff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 11 (Thread 0x7f8b8a3ff700 (LWP 13330)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8b8a3ff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 10 (Thread 0x7f8bc47ff700 (LWP 20189)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8bc47ff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 9 (Thread 0x7f8b7fbff700 (LWP 17522)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8b7fbff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 8 (Thread 0x7f8b71bff700 (LWP 17530)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8b71bff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 7 (Thread 0x7f8bd7fff700 (LWP 20183)):
#0 0x00007f8bebfa574d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x00007f8bee0ad1b5 in ?? () from /usr/lib/x86_64-linux-gnu/libmemcached.so.11
#2 0x00007f8bee0adaad in ?? () from /usr/lib/x86_64-linux-gnu/libmemcached.so.11
#3 0x00007f8bee0ae148 in ?? () from /usr/lib/x86_64-linux-gnu/libmemcached.so.11
#4 0x00007f8bee0b0418 in ?? () from /usr/lib/x86_64-linux-gnu/libmemcached.so.11
#5 0x00007f8bee0b107e in ?? () from /usr/lib/x86_64-linux-gnu/libmemcached.so.11
#6 0x00007f8bee0aa0e2 in memcached_fetch_result () from /usr/lib/x86_64-linux-gnu/libmemcached.so.11
#7 0x0000000003186d46 in HPHP::c_Memcached_ni_getbykey(HPHP::ObjectData*, HPHP::String const&, HPHP::String const&, HPHP::Variant const&, HPHP::VRefParamValue const&) ()
#8 0x0000000005cb189e in ?? ()
#9 0x0000000005c0006f in ?? ()
#10 0x00007f8bd7ffc770 in ?? ()
#11 0x00007f8bd7ffc680 in ?? ()
#12 0x0000000003ec7a84 in HPHP::jit::enterTCImpl(unsigned char*, HPHP::ActRec*) ()
#13 0x0000000005ca60d2 in ?? ()
#14 0x00007f8bda4c1880 in ?? ()
#15 0x000000040000004e in ?? ()
#16 0x00007f8bc64073b0 in ?? ()
#17 0x0000000000000000 in ?? ()

Thread 6 (Thread 0x7f8b9c7ff700 (LWP 26592)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8b9c7ff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 5 (Thread 0x7f8ba2bff700 (LWP 22131)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8ba2bff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 4 (Thread 0x7f8bca7ff700 (LWP 20188)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8bca7ff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 3 (Thread 0x7f8b86bff700 (LWP 14433)):
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x0000000003ff6372 in HPHP::SynchronizableMulti::wait(int, int, HPHP::SynchronizableMulti::Priority) ()
#2 0x000000000182b9c5 in HPHP::JobQueueWorker::start() ()
#3 0x0000000000dbedcf in HPHP::AsyncFuncImpl::threadFuncImpl() ()
#4 0x0000000000dbf0f2 in HPHP::AsyncFuncImpl::ThreadFunc(void*) ()
#5 0x00007f8bf22c46ba in start_thread (arg=0x7f8b86bff700) at pthread_create.c:333
#6 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 2 (Thread 0x7f8bdff0e700 (LWP 20174)):
#0 0x00007f8bebfa574d in poll () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000000001aa44a6 in std::thread::_Impl >::_M_run() ()
#2 0x00007f8bec84bc80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3 0x00007f8bf22c46ba in start_thread (arg=0x7f8bdff0e700) at pthread_create.c:333
#4 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109

Thread 1 (Thread 0x7f8bcbfff700 (LWP 20186)):
#0 0x00007f8bf22ce269 in raise (sig=11) at ../sysdeps/unix/sysv/linux/pt-raise.c:35
#1 0x0000000001415c20 in HPHP::bt_handler(int, siginfo_t*, void*) ()
#2
#3 0x0000000003540083 in facebook::common::mysql_client::AsyncConnectionPool::ConnStorage::cleanupConnections() ()
#4 0x0000000003540558 in facebook::common::mysql_client::AsyncConnectionPool::CleanUpTimer::timeoutExpired() ()
#5 0x0000000003750532 in folly::AsyncTimeout::libeventCallback(int, short, void*) ()
#6 0x00007f8bf31bf4c9 in event_base_loop () from /usr/lib/x86_64-linux-gnu/libevent-2.0.so.5
#7 0x0000000003f61780 in folly::EventBase::loopBody(int, bool) ()
#8 0x0000000003755ba4 in folly::EventBase::loopForever() ()
#9 0x0000000003556bf0 in std::thread::_Impl >::_M_run() ()
#10 0x00007f8bec84bc80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#11 0x00007f8bf22c46ba in start_thread (arg=0x7f8bcbfff700) at pthread_create.c:333
#12 0x00007f8bebfb141d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
```