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use crate::{buf::WriteBuffer, wmap::DataSlice, wmap::WMap, Arc, Data, Limits, Storage};
/// Alternative to AtomicFile.
pub struct BasicAtomicFile {
/// The main underlying storage.
stg: WriteBuffer,
/// Temporary storage for updates during commit.
upd: WriteBuffer,
/// Map of writes. Note the key is the file address of the last byte written.
pub map: WMap,
///
list: Vec<(u64, DataSlice)>,
///
size: u64,
}
impl BasicAtomicFile {
/// stg is the main underlying storage, upd is temporary storage for updates during commit.
pub fn new(stg: Box<dyn Storage>, upd: Box<dyn Storage>, lim: &Limits) -> Box<Self> {
let size = stg.size();
let mut result = Box::new(Self {
stg: WriteBuffer::new(stg, lim.swbuf),
upd: WriteBuffer::new(upd, lim.uwbuf),
map: WMap::default(),
list: Vec::new(),
size,
});
result.init();
result
}
/// Apply outstanding updates.
fn init(&mut self) {
let end = self.upd.stg.read_u64(0);
let size = self.upd.stg.read_u64(8);
if end == 0 {
return;
}
assert!(end == self.upd.stg.size());
let mut pos = 16;
while pos < end {
let start = self.upd.stg.read_u64(pos);
pos += 8;
let len = self.upd.stg.read_u64(pos);
pos += 8;
let mut buf = vec![0; len as usize];
self.upd.stg.read(pos, &mut buf);
pos += len;
self.stg.write(start, &buf);
}
self.stg.commit(size);
self.upd.commit(0);
}
/// Perform the specified phase ( 1 or 2 ) of a two-phase commit.
pub fn commit_phase(&mut self, size: u64, phase: u8) {
if self.map.map.is_empty() && self.list.is_empty() {
return;
}
if phase == 1 {
/* Get list of updates, compare with old data to reduce the size of upd file */
if false {
/*
let mut buf = Vec::new();
for (k, v) in self.map.map.iter() {
let start = k + 1 - v.len as u64;
let len = v.len;
if buf.len() < len {
buf.resize(len, 0);
}
self.stg.read(start, &mut buf[0..len]);
util::diff(&v.data[v.off..v.off + len], &buf, 17, |off, len| {
self.list.push((
start + off as u64,
DataSlice {
off: v.off + off,
len,
data: v.data.clone(),
},
));
});
}
*/
} else {
for (k, v) in self.map.map.iter() {
let start = k + 1 - v.len as u64;
let len = v.len;
self.list.push((
start,
DataSlice {
off: v.off,
len,
data: v.data.clone(),
},
));
}
}
// println!("Commit # writes={}", self.list.len());
self.map.map.clear();
// Write the updates to upd.
// First set the end position to zero.
self.upd.write_u64(0, 0);
self.upd.write_u64(8, size);
self.upd.commit(16); // Not clear if this is necessary.
// Write the update records.
let mut stg_written = false;
let mut pos: u64 = 16;
for (start, v) in self.list.iter() {
let len = v.len as u64;
let start = *start;
let data = &v.data[v.off..v.off + v.len];
if start >= self.size {
// Writes beyond current stg size can be written directly.
stg_written = true;
self.stg.write(start, data);
} else {
self.upd.write_u64(pos, start);
pos += 8;
self.upd.write_u64(pos, len);
pos += 8;
self.upd.write(pos, data);
pos += len;
}
}
if stg_written {
self.stg.commit(size);
}
self.upd.commit(pos); // Not clear if this is necessary.
// Set the end position.
self.upd.write_u64(0, pos);
self.upd.write_u64(8, size);
self.upd.commit(pos);
} else {
for (start, v) in self.list.iter() {
let start = *start;
if start < self.size {
// Writes beyond current stg size have already been written.
self.stg.write(start, &v.data[v.off..v.off + v.len]);
}
}
self.list.clear();
self.stg.commit(size);
self.upd.commit(0);
}
}
}
impl Storage for BasicAtomicFile {
fn commit(&mut self, size: u64) {
self.commit_phase(size, 1);
self.commit_phase(size, 2);
self.size = size;
}
fn size(&self) -> u64 {
self.size
}
fn read(&self, start: u64, data: &mut [u8]) {
self.map.read(start, data, &*self.stg.stg);
}
fn write_data(&mut self, start: u64, data: Data, off: usize, len: usize) {
self.map.write(start, data, off, len);
}
fn write(&mut self, start: u64, data: &[u8]) {
let len = data.len();
let d = Arc::new(data.to_vec());
self.write_data(start, d, 0, len);
}
}