# mmap-vecdeque
`mmap-vecdeque` is a file-backed, memory-mapped, durable, and thread-safe double-ended queue (deque) for Rust. Unlike a normal `VecDeque`, operations aren't immediately durable. Instead, you can batch multiple insertions, deletions, etc., and then call `commit()` to atomically persist all changes to disk.
## Key Features
- **Deferred commits:** Changes are kept in memory until `commit()` is called.
- **Atomic and durable commits:** Once `commit()` returns, all changes are atomically and durably persisted to disk.
- **Configurable chunk size:** Items are stored in fixed-size chunks of elements. By default, 10,000 elements per chunk.
- **Mmap-backed:** Data is accessed via memory mapping for potentially high performance.
- **Iterators:** `iter()` and `iter_mut()` to traverse elements.
## Usage
```rust
use mmap_vecdeque::{MmapVecDeque, MmapVecDequeError};
use std::path::Path;
fn main() -> Result<(), MmapVecDequeError> {
let dir = Path::new("my_deque_storage");
let mut deque = MmapVecDeque::<u64>::open_or_create(dir, None)?;
deque.push_back(42)?;
deque.push_front(1)?;
// Changes are not yet durable on disk
deque.commit()?; // Now 1 and 42 are atomically committed.
println!("Front: {:?}", deque.front()); // Some(1)
println!("Back: {:?}", deque.back()); // Some(42)
deque.pop_front()?;
// Not durable yet.
deque.commit()?; // commit again
println!("Front after pop: {:?}", deque.front()); // Some(42)
// Iteration
for val in deque.iter() {
println!("{}", val);
}
Ok(())
}
```