sled: Cannot shutdown sled from Windows Service

1. sled version 0.28.0
2. rustc version 1.39.0
3. operating system Windows 10 Enterprise 1809 Build 17763.864
4. logs

When I try to join my main thread after receiving the stop signal, I have 2 sled threads that are not terminating.

The Db and Trees are stored using RwLock:

pub struct Table {
    pub arc_tree_lock: RwLock<Option<Arc<Tree>>>,
    name: String,
    key: String,
    key2_opt: Option<String>,
}

pub struct MyDb {
    pub my_db: Arc<RwLock<Option<Db>>>,
    db_name: String,

When I get the Windows service stop, for each Tree I call flush() and then I set the option to None to de-reference the Tree after taking the lock.

When done, I set my_db to None to de-reference the DB.

However, I have 2 threads still waiting that prevent the final join from completing, it was 3 including the log flusher, but after the code to flush then set option to None, at least the log flusher seems to have cleaned up.

The 2 are sled-io with the following stack trace (after break all):

 	[External Code]	
 	[Inline Frame] my.exe!!std::sys::windows::c::SleepConditionVariableSRW() Line 70	Unknown
 	[Inline Frame] my.exe!!std::sys::windows::condvar::Condvar::wait() Line 22	Unknown
 	[Inline Frame] my.exe!!std::sys_common::condvar::Condvar::wait() Line 41	Unknown
 	[Inline Frame] my.exe!!std::sync::condvar::Condvar::wait() Line 204	Unknown
 	my.exe!std::thread::park() Line 911	Unknown
 	my.exe!!crossbeam_channel::context::Context::wait_until(core::option::Option<std::time::Instant> self) Line 175	Unknown
 	my.exe!!crossbeam_channel::flavors::zero::{{impl}}::recv::{{closure}}<alloc::boxed::Box<FnOnce<()>>>(crossbeam_channel::flavors::zero::{{impl}}::recv::closure-1 cx, crossbeam_channel::context::Context *) Line 304	Unknown
 	my.exe!!crossbeam_channel::context::{{impl}}::with::{{closure}}<closure-1,core::result::Result<alloc::boxed::Box<FnOnce<()>>, crossbeam_channel::err::RecvTimeoutError>>(crossbeam_channel::context::{{impl}}::with::closure-0 * cx, crossbeam_channel::context::Context *) Line 51	Unknown
 	my.exe!!crossbeam_channel::context::{{impl}}::with::{{closure}}<closure-1,core::result::Result<alloc::boxed::Box<FnOnce<()>>, crossbeam_channel::err::RecvTimeoutError>>(crossbeam_channel::context::{{impl}}::with::closure-1 cell, core::cell::Cell<core::option::Option<crossbeam_channel::context::Context>> *) Line 58	Unknown
 	my.exe!!std::thread::local::LocalKey<core::cell::Cell<core::option::Option<crossbeam_channel::context::Context>>>::try_with<core::cell::Cell<core::option::Option<crossbeam_channel::context::Context>>,closure-1,core::result::Result<alloc::boxed::Box<FnOnce<()>>, crossbeam_channel::err::RecvTimeoutError>>(crossbeam_channel::context::{{impl}}::with::closure-1 self) Line 262	Unknown
>	my.exe!!crossbeam_channel::context::Context::with<closure-1,core::result::Result<alloc::boxed::Box<FnOnce<()>>, crossbeam_channel::err::RecvTimeoutError>>(crossbeam_channel::flavors::zero::{{impl}}::recv::closure-1 f) Line 53	Unknown
 	my.exe!!crossbeam_channel::flavors::zero::Channel<alloc::boxed::Box<FnOnce<()>>>::recv<alloc::boxed::Box<FnOnce<()>>>(core::option::Option<std::time::Instant> self) Line 293	Unknown
 	my.exe!!crossbeam_channel::channel::Receiver<alloc::boxed::Box<FnOnce<()>>>::recv<alloc::boxed::Box<FnOnce<()>>>() Line 718	Unknown
 	my.exe!!crossbeam_channel::channel::{{impl}}::next<alloc::boxed::Box<FnOnce<()>>>(crossbeam_channel::channel::Iter<alloc::boxed::Box<FnOnce<()>>> * self) Line 1105	Unknown
 	my.exe!!pagecache::threadpool::spawn::init_pool::{{closure}}(pagecache::threadpool::spawn::init_pool::closure-0) Line 54	Unknown
 	my.exe!!std::sys_common::backtrace::__rust_begin_short_backtrace<closure-0,()>(pagecache::threadpool::spawn::init_pool::closure-0 f) Line 127	Unknown
 	my.exe!!std::thread::{{impl}}::spawn_unchecked::{{closure}}::{{closure}}<closure-0,()>(std::thread::{{impl}}::spawn_unchecked::{{closure}}::closure-0) Line 471	Unknown
 	my.exe!!std::panic::{{impl}}::call_once<(),closure-0>(std::panic::AssertUnwindSafe<closure-0> self) Line 316	Unknown
 	my.exe!!std::panicking::try::do_call<std::panic::AssertUnwindSafe<closure-0>,()>(unsigned char * data) Line 292	Unknown
 	my.exe!!panic_unwind::__rust_maybe_catch_panic() Line 80	Unknown
 	my.exe!!std::panicking::try<(),std::panic::AssertUnwindSafe<closure-0>>(std::panic::AssertUnwindSafe<closure-0> f) Line 271	Unknown
 	my.exe!!std::panic::catch_unwind<std::panic::AssertUnwindSafe<closure-0>,()>(std::panic::AssertUnwindSafe<closure-0> f) Line 394	Unknown
 	my.exe!!std::thread::{{impl}}::spawn_unchecked::{{closure}}<closure-0,()>(std::thread::{{impl}}::spawn_unchecked::closure-0) Line 469	Unknown
 	my.exe!!core::ops::function::FnOnce::call_once<closure-0,()>(std::thread::{{impl}}::spawn_unchecked::closure-0 *) Line 227	Unknown
 	my.exe!!alloc::boxed::{{impl}}::call_once<(),FnOnce<()>>() Line 922	Unknown
 	[Inline Frame] my.exe!!alloc::boxed::{{impl}}::call_once() Line 922	Unknown
 	[Inline Frame] my.exe!!std::sys_common::thread::start_thread() Line 13	Unknown
 	my.exe!e!std::sys::windows::thread::{{impl}}::new::thread_start() Line 47	Unknown
 	[External Code]