From 75578432bb61c09715f3389734f9cdbf285cb9d5 Mon Sep 17 00:00:00 2001
From: Determinant <tederminant@gmail.com>
Date: Tue, 9 Jun 2020 14:54:00 -0400
Subject: ...

---
 src/lib.rs | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 58 insertions(+), 4 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index e4ae0ea..2716cb5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,5 @@
+use std::collections::BinaryHeap;
+
 #[repr(u8)]
 enum WALRingType {
     Null = 0x0,
@@ -16,10 +18,27 @@ struct WALRingBlob {
 
 type WALFileId = u32;
 type WALPos = u64;
-type WALWrite = (WALPos, Box<[u8]>);
+
+#[derive(Eq, PartialEq, Copy, Clone)]
+pub struct WALRingId {
+    start: WALPos,
+    end: WALPos
+}
+
+impl Ord for WALRingId {
+    fn cmp(&self, other: &WALRingId) -> std::cmp::Ordering {
+        other.start.cmp(&self.start).then_with(|| other.end.cmp(&self.end))
+    }
+}
+
+impl PartialOrd for WALRingId {
+    fn partial_cmp(&self, other: &WALRingId) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
 
 pub struct WALState {
-    pub base: WALPos,
+    pub first_fid: u64,
     pub last: WALPos,
     pub block_nbit: u8,
     pub file_nbit: u8,
@@ -53,6 +72,9 @@ impl<F: WALStore> WALFilePool<F> {
     }
     fn write(&mut self, offset: u64, data: Box<[u8]>) {
     }
+    fn remove_file(&self, fid: u64) -> bool {
+        true
+    }
 }
 
 pub struct WALWriter<F: WALStore> {
@@ -60,6 +82,8 @@ pub struct WALWriter<F: WALStore> {
     file_pool: WALFilePool<F>,
     block_buffer: Box<[u8]>,
     block_size: u32,
+    next_complete: WALPos,
+    io_complete: BinaryHeap<WALRingId>
 }
 
 impl<F: WALStore> WALWriter<F> {
@@ -73,10 +97,16 @@ impl<F: WALStore> WALWriter<F> {
             file_pool: WALFilePool::new(wal_store, file_size, cache_size),
             block_buffer: b.into_boxed_slice(),
             block_size,
+            next_complete: 0,
+            io_complete: BinaryHeap::new(),
         }
     }
 
-    pub fn grow(&mut self, records: &[Box<[u8]>]) {
+    /// Submit a sequence of records to WAL; WALStore/WALFile callbacks are invoked before the
+    /// function returns.  The caller then has the knowledge of WAL writes so it should defer
+    /// actual data writes after WAL writes.
+    pub fn grow(&mut self, records: &[Box<[u8]>]) -> Box<[WALRingId]> {
+        let mut res = Vec::new();
         let mut writes = Vec::new();
         let msize = std::mem::size_of::<WALRingBlob>() as u32;
         // the global offest of the begining of the block
@@ -95,6 +125,7 @@ impl<F: WALStore> WALWriter<F> {
                     let d = remain - msize;
                     let blob = unsafe {std::mem::transmute::<*mut u8, &mut WALRingBlob>(
                         &mut self.block_buffer[bbuff_cur as usize] as *mut u8)};
+                    let ring_start = self.state.last + (bbuff_cur - bbuff_start) as u64;
                     if d >= rsize {
                         // the remaining rec fits in the block
                         let payload = rec;
@@ -118,6 +149,8 @@ impl<F: WALStore> WALWriter<F> {
                         bbuff_cur += d;
                         rec = &rec[d as usize..];
                     }
+                    let ring_end = self.state.last + (bbuff_cur - bbuff_start) as u64;
+                    res.push(WALRingId{start: ring_start, end: ring_end});
                 } else {
                     // add padding space by moving the point to the end of the block
                     bbuff_cur = self.block_size;
@@ -139,7 +172,28 @@ impl<F: WALStore> WALWriter<F> {
             self.state.last += (bbuff_cur - bbuff_start) as u64;
         }
         for (off, w) in writes.into_iter() {
-            self.file_pool.write(off, w)
+            self.file_pool.write(off, w);
+        }
+        res.into_boxed_slice()
+    }
+
+    /// Inform the WALWriter that data writes (specified by a slice of (offset, length) tuples) are
+    /// complete so that it could automatically remove obsolete WAL files.
+    pub fn peel(&mut self, records: &[WALRingId]) {
+        for rec in records {
+            self.io_complete.push(*rec)
+        }
+        let orig_fid = self.state.first_fid;
+        while let Some(s) = self.io_complete.peek().and_then(|&e| Some(e.start)) {
+            if s != self.next_complete {
+                break
+            }
+            let m = self.io_complete.pop().unwrap();
+            self.next_complete = m.end
+        }
+        let next_fid = self.next_complete >> self.state.file_nbit;
+        for fid in orig_fid..next_fid {
+            self.file_pool.remove_file(fid);
         }
     }
 }
-- 
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