During some lock debugging on a dual-core Linux system I noticed that threads are blocked acquiring `cs_vNodes` and `cs_main` for long periods when the system is under moderate load from unrelated processes -- the unlucky lock acquirer is waiting for single-digit seconds once every 10 minutes or so (not coinciding with new blocks) up to around a 30 second wait every few hours. It looks like `ThreadMessageHandler` is taking locks and then due to being set to `THREAD_PRIORITY_BELOW_NORMAL`, it's being descheduled (even in trivial lock-holding regions like `GetHeight`) and holding up for arbitrarily long periods other threads that use these core locks.

So I'm wondering, what are the benefits of running the message handler at low priority?

#if defined(HAVE_CONFIG_H)
#include "config/bitcoin-config.h"
#endif
#include "util.h"
#include "chainparamsbase.h"
#include "random.h"
#include "serialize.h"
#include "sync.h"
#include "utilstrencodings.h"
#include "utiltime.h"
#include <stdarg.h>
#if (defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__))
#include <pthread.h>
#include <pthread_np.h>
#endif
#ifndef WIN32
#ifdef __linux__
#ifdef _POSIX_C_SOURCE
#undef _POSIX_C_SOURCE
#endif
#define _POSIX_C_SOURCE 200112L
#endif 
#include <algorithm>
#include <fcntl.h>
#include <sys/resource.h>
#include <sys/stat.h>