fragile 2.0.0

Provides wrapper types for sending non-send values to other threads.
Documentation
# Fragile

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This library provides wrapper types that permit sending non Send types to other
threads and use runtime checks to ensure safety.

It provides the `Fragile<T>`, `Sticky<T>` and `SemiSticky<T>` types which are
similar in nature but have different behaviors with regards to how destructors
are executed.  The `Fragile<T>` will panic if the destructor is called in another
thread, `Sticky<T>` will temporarily leak the object until the thread shuts down.
`SemiSticky<T>` is a compromise of the two.  It behaves like `Sticky<T>` but it
avoids the use of thread local storage if the type does not need `Drop`.

## Example

```rust
use std::thread;

// creating and using a fragile object in the same thread works
let val = Fragile::new(true);
assert_eq!(*val.get(), true);
assert!(val.try_get().is_ok());

// once send to another thread it stops working
thread::spawn(move || {
    assert!(val.try_get().is_err());
}).join()
    .unwrap();
```

## License and Links

- [Documentation]https://docs.rs/fragile/
- [Issue Tracker]https://github.com/mitsuhiko/fragile/issues
- License: [Apache 2.0]https://github.com/mitsuhiko/fragile/blob/master/LICENSE