Crate ticketed_lock

Ticketed lock.

Ticketed lock is similar to RwLock, except that the acquisition of the lock is split:

1. obtaining a ticket, which has to be done on the same thread as the locked storage
2. waiting on a ticket, which puts the current thread to sleep until the ticket is due. That moment comes when all the previous tickets are processed.
3. working with the data behind a read/lock guard
4. when the guard is freed, it allows the following tickets to become active

A ticket can be moved between threads or even just lost. Consecutive read-only tickets do not guarantee a particular lock order. All the ticket counting is done based on Arc primitives, and the only unsafe code that this library has is for accessing the actual data behind a guard.

Structs

ReadLockGuard	The read-only guard of data, allowing &T dereferences.
ReadTicket	A ticket to read the data at some point.
TicketedLock	The ticketed lock, which wraps the data.
WriteLockGuard	The read/write guard of data, allowing &mut T dereferences.
WriteTicket	A ticket to read/write the data at some point.