SIGSEGV running safe code

[AlisdairO]

While messing around with the benchmarks today I ran into the following:

test pool_individual ... thread '<unnamed>' panicked at 'thread 'bad number of channels left 0<unnamed>', ' panicked at '../src/libstd/sync/mpsc/shared.rsbad number of channels left -2:', ../src/libstd/sync/mpsc/shared.rs:346346

stack backtrace:
thread '<unnamed>' panicked at 'bad number of channels left -1', ../src/libstd/sync/mpsc/shared.rs:346
thread '<unnamed>' panicked at 'bad number of channels left -3', ../src/libstd/sync/mpsc/shared.rs:346
   1:        0x1018cf408 - sys::backtrace::tracing::imp::write::hd2c80f5e6164b288Sju
   2:        0x1018d0ec5 - panicking::default_handler::_$u7b$$u7b$closure$u7d$$u7d$::closure.42908
   3:        0x1018d0ae8 - panicking::default_handler::h36a516d1790b538eZDy
   4:        0x1018c6136 - sys_common::unwind::begin_unwind_inner::h6bef346cfa00530fajt
   5:        0x1018c65ae - sys_common::unwind::begin_unwind_fmt::hd46a8bf3b027ae6agit
   6:        0x10185eb76 - std..sync..mpsc..Sender<bool>::drop.6710::hc9f776eb327502e7
   7:        0x10186a45d - simple_parallel::pool::Pool::unordered_map::thread '_<unnamed>$u7b$$u7b$closure$u7d$$u7d$' panicked at '::bad number of channels left 0_', $u7b$$u7b$closure$u7d$$u7d$../src/libstd/sync/mpsc/shared.rs:::closure.7131346

   8:        0x1018c1030 - sys_common::unwind::try::try_fn::h11016301218827575359
thread '<unnamed>' panicked at 'called 'Option::unwrap()' on a 'None' value', ../src/libcore/option.rs:330  
 9:    thread ' <unnamed> ' panicked at ' bad number of channels left 0 ', 0x../src/libstd/sync/mpsc/shared.rs1018ce83b: - 346__rust_try

  10:        0x1018cc513 - sys_commonthread '::<unnamed>unwind' panicked at '::called 'Option::unwrap()' on a 'None' valueinner_try', ::../src/libcore/option.rsh0d91b1e766cf5ae7cgt:
330
  thread '11<unnamed>: ' panicked at ' bad number of channels left 0 ',  ../src/libstd/sync/mpsc/shared.rs : 346 
 0x1018c2117 - boxed::F.FnBox<A>::call_box::h9811097413934130002
  12:       thread ' <unnamed>0x' panicked at '1018d014f - sys::thread::Thread::new::thread_startbad number of channels left -1::h964aafa589ae520eqSx
', ../src/libstd/sync/mpsc/shared.rs:  34613
:     0x7fff91057898 - _pthread_body
  14:     0x7fff91057729 - _pthread_start
stack backtrace:
   1:        0x1018cf408 - sys::backtrace::tracing::imp::write::hd2c80f5e6164b288Sju
   2:        0x1018d0ec5 - panicking::default_handler::_$u7b$$u7b$closure$u7d$$u7d$::closure.42908
   3:        0x1018d0ae8 - panicking::default_handler::h36a516d1790b538eZDy
   4:        0x1018c6136 - sys_common::unwind::begin_unwind_inner::h6bef346cfa00530fajt
   5:        0x1018c65ae - sys_common::unwind::begin_unwind_fmt::hd46a8bf3b027ae6agit
   6:        0x10185eb76 - std..sync..mpsc..Sender<bool>::drop.6710::hc9f776eb327502e7
   7:        0x10186a45d - simple_parallel::pool::Pool::unordered_map::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::closure.7131
   8:   thread ' <unnamed> ' panicked at ' bad number of channels left -1 ',  ../src/libstd/sync/mpsc/shared.rs0x:1018c1030346 - 
sys_common::unwind::try::try_fn::h11016301218827575359
   9:        0x1018ce83bthread ' - <unnamed>__rust_try' panicked at '
bad number of channels left 0', ../src/libstd/sync/mpsc/shared.rs:346
  10:        0x1018cc513 - thread 'sys_common<unnamed>::' panicked at 'unwindbad number of channels left -4::', inner_try../src/libstd/sync/mpsc/shared.rs:::h0d91b1e766cf5ae7cgt346

  11:      thread '  <unnamed>0x' panicked at '1018c2117bad number of channels left -2 - ', ../src/libstd/sync/mpsc/shared.rsboxed:::346F.FnBox
<A>::call_box::h9811097413934130002
  12:  thread ' <unnamed> ' panicked at ' bad number of channels left -6 ',  ../src/libstd/sync/mpsc/shared.rs :0x3461018d014f
 - sys::thread::Thread::new::thread_start::h964aafa589ae520eqSx
thread '  <unnamed>13' panicked at ': bad number of channels left -5 ',  ../src/libstd/sync/mpsc/shared.rs : 3460x
7fff91057898 - _pthread_body
  14:     0x7fff91057729 - _pthread_start
thread '<unnamed>' panicked at 'bad number of channels left -3', ../src/libstd/sync/mpsc/shared.rs:346
stack backtrace:
   1:        0x1018cf408 - sys::backtrace::tracing::imp::write::hd2c80f5e6164b288Sju
   2:        0x1018d0ec5 - panicking::default_handler::_$u7b$$u7b$closure$u7d$$u7d$::closure.42908
   3:        0x1018d0ae8 - panicking::default_handler::h36a516d1790b538eZDy
   4:        0x1018c6136 - sys_common::unwind::begin_unwind_inner::h6bef346cfa00530fajt
   5:        0x1018c65ae - sys_common::unwind::begin_unwind_fmt::hd46a8bf3b027ae6agit
   6:        0x10185eb76 - std..sync..mpsc..Sender<bool>::drop.6710::hc9f776eb327502e7
   7:        0x10186a45d - simple_parallel::pool::Pool::unordered_map::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::closure.7131
   8:        0x1018c1030 - sys_common::unwind::try::try_fn::h11016301218827575359
   9:        0x1018ce83b - __rust_try
  10:        0x1018cc513 - sys_common::unwind::inner_try::h0d91b1e766cf5ae7cgt
  11:        0x1018c2117 - boxed::F.FnBox<A>::call_box::h9811097413934130002
  12:        0x1018d014f - sys::thread::Thread::new::thread_start::h964aafa589ae520eqSx
  13: thread ' <unnamed> ' panicked at ' called 'Option::unwrap()' on a 'None' value ', 0x7fff91057898../src/libcore/option.rs - :_pthread_body330

Process didn't exit successfully: '/Users/alisdair/coding/rust/simple_parallel/target/release/transform-151cdb951485d908 --bench' (signal: 11, SIGSEGV: invalid memory reference)

This/similar errors are repeatable on my machine using the following code:

fn run<F>(b: &mut test::Bencher, mut f: F) where F: FnMut(&[&[i32]]) -> i32 {
    let v = vec![0; 10];
    let w = vec![&*v; 50];
    b.iter(|| {
        f(test::black_box(&w))
    })  
}

fn sum<I: Iterator<Item = i32>>(iter: I) -> i32 {
    //iter.fold(0, |a, b| a + b)
    0   
}

#[bench]
fn pool_individual(b: &mut test::Bencher) {
    let mut pool = simple_parallel::Pool::new(num_cpus::get());
    run(b, |w| {
        crossbeam::scope(|scope| {
            sum(pool.unordered_map(scope, w, |v: &&[i32]| sum(v.iter().cloned())).map(|(_,t)| t)) 
        })  
    })  
}