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use std::collections::HashMap;
use std::mem;
use std::sync::Arc;
use memory::mmap_type::MmapSlice;
use parking_lot::{Mutex, RwLock};
use crate::common::Flusher;
/// A wrapper around `MmapSlice` that delays writing changes to the underlying file until they get
/// flushed manually.
/// This expects the underlying MmapSlice not to grow in size.
#[derive(Debug)]
pub struct MmapSliceBufferedUpdateWrapper<T>
where
T: 'static,
{
mmap_slice: Arc<RwLock<MmapSlice<T>>>,
len: usize,
pending_updates: Mutex<HashMap<usize, T>>,
}
impl<T> MmapSliceBufferedUpdateWrapper<T>
where
T: 'static,
{
pub fn new(mmap_slice: MmapSlice<T>) -> Self {
let len = mmap_slice.len();
Self {
mmap_slice: Arc::new(RwLock::new(mmap_slice)),
len,
pending_updates: Mutex::new(HashMap::new()),
}
}
/// Sets the item at `index` to `value` buffered.
///
/// ## Panics
/// Panics if the index is out of bounds.
pub fn set(&self, index: usize, value: T) {
assert!(index < self.len, "index {index} out of range: {}", self.len);
self.pending_updates.lock().insert(index, value);
}
}
impl<T> MmapSliceBufferedUpdateWrapper<T>
where
T: 'static + Sync + Send,
{
pub fn flusher(&self) -> Flusher {
let pending_updates = mem::take(&mut *self.pending_updates.lock());
let slice = self.mmap_slice.clone();
Box::new(move || {
let mut mmap_slice_write = slice.write();
for (index, value) in pending_updates {
mmap_slice_write[index] = value;
}
Ok(mmap_slice_write.flusher()()?)
})
}
}
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