dangleptr

``` (gdb) bt #0 0x000000000079cf5b in folly::ThreadLocalPtr::get (this=0x7f4ad8001760) at /home/heng/workspace/folly/folly/ThreadLocal.h:159 #1 0x000000000079740c in folly::ThreadLocal::get (this=0x7f4ad8001760) at /home/heng/workspace/folly/folly/ThreadLocal.h:68 #2 folly::ThreadLocal::operator* (this=0x7f4ad8001760) at /home/heng/workspace/folly/folly/ThreadLocal.h:77 #3 0x0000000000794d35 in folly::SingletonThreadLocal::getWrapper () at /home/heng/workspace/folly/folly/SingletonThreadLocal.h:148 #4...

It seems that in IOThreadPool, the thread local variable has been released when accessing it. Any thoughts?

centos 7.5 + gcc 8.3.0 @boringuy

thread_pool_executor_test SegFault on v2020.4.20 with the similar error. ``` #0 0x00000000009cac61 in folly::ThreadLocalPtr::get (this=0x7f6e94000af0) at /home/vesoft/data/chenheng/3rd/folly/folly/ThreadLocal.h:160 #1 0x00000000009ca0dc in folly::ThreadLocal::get (this=0x7f6e94000af0) at /home/vesoft/data/chenheng/3rd/folly/folly/ThreadLocal.h:69 #2 folly::ThreadLocal::operator* ( this=0x7f6e94000af0) at /home/vesoft/data/chenheng/3rd/folly/folly/ThreadLocal.h:78 #3...