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use std::collections::HashMap;
use std::mem;
use std::sync::Arc;
use memory::mmap_type::MmapBitSlice;
use parking_lot::{Mutex, RwLock};
use crate::common::Flusher;
/// A wrapper around `MmapBitSlice` that delays writing changes to the underlying file until they get
/// flushed manually.
/// This expects the underlying MmapBitSlice not to grow in size.
#[derive(Debug)]
pub struct MmapBitSliceBufferedUpdateWrapper {
bitslice: Arc<RwLock<MmapBitSlice>>,
len: usize,
pending_updates: Mutex<HashMap<usize, bool>>,
}
impl MmapBitSliceBufferedUpdateWrapper {
pub fn new(bitslice: MmapBitSlice) -> Self {
let len = bitslice.len();
Self {
bitslice: Arc::new(RwLock::new(bitslice)),
len,
pending_updates: Mutex::new(HashMap::new()),
}
}
/// Sets the bit at `index` to `value` buffered.
///
/// ## Panics
/// Panics if the index is out of bounds.
pub fn set(&self, index: usize, value: bool) {
assert!(index < self.len, "index {index} out of range: {}", self.len);
self.pending_updates.lock().insert(index, value);
}
pub fn get(&self, index: usize) -> Option<bool> {
if index >= self.len {
return None;
}
if let Some(value) = self.pending_updates.lock().get(&index) {
Some(*value)
} else {
self.bitslice.read().get(index).as_deref().copied()
}
}
pub fn len(&self) -> usize {
self.len
}
pub fn is_empty(&self) -> bool {
self.len == 0
}
pub fn flusher(&self) -> Flusher {
let pending_updates = mem::take(&mut *self.pending_updates.lock());
let bitslice = self.bitslice.clone();
Box::new(move || {
let mut mmap_slice_write = bitslice.write();
for (index, value) in pending_updates {
mmap_slice_write.set(index, value);
}
Ok(mmap_slice_write.flusher()()?)
})
}
}
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