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provide better debugging facilities for nondeterministic tests #184

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provide better debugging facilities for nondeterministic tests #184

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Commits on Oct 26, 2020

  1. provide better debugging facilities for nondeterministic tests 

    This change adds a new tracing facility that helps track down the source of
nondeterministic execution. It records, for each branch point, the original
(user) source code position leading to this branch, the operation being
performed, and the reference that is involved in the branch. If this does not
match on a later execution, we dump the mismatched operation, as well as a
trace of recent operations, let the current execution run to completion, then
panic.

A typical trace looks a bit like this:

```
===== NONDETERMINISTIC EXECUTION DETECTED =====
Previous execution:
    13: [tests/nondet.rs:55:28] loom::thread::JoinHandle<()>::join on Thread::2

Current execution:
    13: [tests/nondet.rs:55:28] loom::thread::JoinHandle<()>::join on Thread::3

Recent events:
       0: [tests/nondet.rs:17:26] loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>::lock on Mutex::0
       1: [tests/nondet.rs:18:19] loom::sync::arc::Arc<loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>>::clone on State::1
       2: [tests/nondet.rs:35:9] loom::thread::yield_now
     ...: THREAD SWITCH on Thread::1
       3: [tests/nondet.rs:21:30] loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>::lock on Mutex::0
     ...: THREAD SWITCH on Thread::0
     ...: loom::sync::mutex::MutexGuard<nondet::nondeterministic_execution_detected::State>::drop on Mutex::0
       4: [tests/nondet.rs:17:26] loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>::lock on Mutex::0
       5: [tests/nondet.rs:18:19] loom::sync::arc::Arc<loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>>::clone on State::1
       6: [tests/nondet.rs:35:9] loom::thread::yield_now
     ...: THREAD SWITCH on Thread::2
       7: [tests/nondet.rs:21:30] loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>::lock on Mutex::0
     ...: THREAD SWITCH on Thread::0
     ...: loom::sync::mutex::MutexGuard<nondet::nondeterministic_execution_detected::State>::drop on Mutex::0
       8: [tests/nondet.rs:17:26] loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>::lock on Mutex::0
       9: [tests/nondet.rs:18:19] loom::sync::arc::Arc<loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>>::clone on State::1
      10: [tests/nondet.rs:35:9] loom::thread::yield_now
     ...: THREAD SWITCH on Thread::3
      11: [tests/nondet.rs:21:30] loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>::lock on Mutex::0
     ...: THREAD SWITCH on Thread::0
     ...: loom::sync::mutex::MutexGuard<nondet::nondeterministic_execution_detected::State>::drop on Mutex::0
      12: [tests/nondet.rs:45:30] loom::sync::mutex::Mutex<nondet::nondeterministic_execution_detected::State>::lock on Mutex::0
     ...: loom::sync::mutex::MutexGuard<nondet::nondeterministic_execution_detected::State>::drop on Mutex::0

thread 'nondeterministic_execution_detected' panicked at 'Aborting due to non-deterministic execution', src/rt/execution.rs:262:13
stack backtrace:
   0: std::panicking::begin_panic
             at /local/home/bdonlan/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/panicking.rs:497
   1: loom::rt::execution::Execution::check_consistency
             at ./src/rt/execution.rs:262
   2: loom::model::Builder::check
             at ./src/model.rs:208
   3: loom::model::model
             at ./src/model.rs:230
   4: nondet::nondeterministic_execution_detected
             at ./tests/nondet.rs:38
   5: nondet::nondeterministic_execution_detected::{{closure}}
             at ./tests/nondet.rs:9
   6: core::ops::function::FnOnce::call_once
             at /local/home/bdonlan/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:227
   7: core::ops::function::FnOnce::call_once
             at /rustc/18bf6b4f01a6feaf7259ba7cdae58031af1b7b39/library/core/src/ops/function.rs:227
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
test nondeterministic_execution_detected ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
```
    Bryan Donlan committed Oct 26, 2020
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  2. update minrust to 1.47.0 

    This is needed for the Eq trait on `std::panic::Location`.
    Bryan Donlan committed Oct 26, 2020
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  3. path: fix panic from branch_spurious

    Bryan Donlan committed Oct 26, 2020
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  4. arc: avoid panics in drops 

    Panicing in drops can result in panic-in-panic events that make debugging
harder than necessary. Make an attempt to catch panics coming from e.g. the
execution being unavailable and just set a flag to cause the test to fail later
instead.
    Bryan Donlan committed Oct 26, 2020
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