Log: fix concurrent overwrite() and compact()

lib/log/index.js

@@ -634,6 +634,11 @@ function Log(filename, opts) {
    * @param {CB<void>} cb
    */
   function overwrite(offset, data, cb) {
+    if (compacting) {
+      waitingCompaction.push(() => overwrite(offset, data, cb))
+      return
+    }
+
     let encodedData = codec.encode(data)
     if (typeof encodedData === 'string') encodedData = b4a.from(encodedData)
 
@@ -707,10 +712,6 @@ function Log(filename, opts) {
    * @param {CB<void>?} cb
    */
   async function compact(cb) {
-    if (compacting) {
-      if (cb) waitingCompaction.push(cb)
-      return
-    }
     cb ??= logError
     const debug2 = debug.extend('compact')
     if (deletedBytes === 0) {
@@ -724,9 +725,13 @@ function Log(filename, opts) {
       // prettier-ignore
       return cb(new Error('Compact failed to pre-flush overwrites', { cause: err1 }))
     }
+    if (compacting) {
+      if (cb) waitingCompaction.push(cb)
+      return
+    }
+    compacting = true
 
     const startCompactTimestamp = Date.now()
-    compacting = true
     if (compactionProgress.value.done) {
       compactionProgress.set(COMPACTION_PROGRESS_START)
     }
@@ -734,6 +739,7 @@ function Log(filename, opts) {
     const filenameNew = filename + '.compacting'
     const [err2] = await p(fs.unlink.bind(fs))(filenameNew)
     if (err2 && err2.code !== 'ENOENT') {
+      compacting = false
       // prettier-ignore
       return cb(new Error('Compact failed to get rid of previous compacting log', { cause: err2 }))
     }
@@ -846,15 +852,16 @@ function Log(filename, opts) {
     const nextSince = latestBlockIndex * blockSize + nextOffsetInBlock
     const sizeDiff = oldTotalBytes - getTotalBytes()
     lastRecOffset.set(nextSince)
-    compacting = false
     const duration = Date.now() - startCompactTimestamp
     debug2('Completed in %d ms', duration)
     deletedBytes = 0
     const [err7] = await p(saveStats)()
     if (err7) {
+      compacting = false
       return cb(new Error('Compact failed to save stats file', { cause: err7 }))
     }
     compactionProgress.set({ percent: 1, done: true, sizeDiff, holesFound })
+    compacting = false
     for (const callback of waitingCompaction) callback()
     waitingCompaction.length = 0
     cb()

test/log/compact.test.js

@@ -30,7 +30,6 @@ test('Log compaction', async (t) => {
     })
 
     await p(log.compact)()
-    await p(log.onDrain)()
 
     assert.deepEqual(
       progressArr,
@@ -88,7 +87,6 @@ test('Log compaction', async (t) => {
     assert('delete first record')
 
     await p(log.compact)()
-    await p(log.onDrain)()
 
     assert.deepEqual(
       progressArr,
@@ -153,7 +151,6 @@ test('Log compaction', async (t) => {
     })
 
     await p(log.compact)()
-    await p(log.onDrain)()
 
     await new Promise((resolve, reject) => {
       const arr = []