SQLite

     { filename: ..., flags: ..., vfs: ... }

     If passed an object, any additional properties it has are copied
     as-is into the new object.
  */
  dbCtorHelper.normalizeArgs = function(filename=':memory:',flags = 'c',vfs = null){
    const arg = {};
    if(1===arguments.length && arguments[0] && 'object'===typeof arguments[0]){
      Object.assign(arg, arguments[0]);

      if(undefined===arg.flags) arg.flags = 'c';
      if(undefined===arg.vfs) arg.vfs = null;
      if(undefined===arg.filename) arg.filename = ':memory:';
    }else{
      arg.filename = filename;
      arg.flags = flags;
      arg.vfs = vfs;

      'SQLITE_LOCK_RESERVED',
      'SQLITE_LOCK_SHARED',
      'SQLITE_LOCKED',
      'SQLITE_MISUSE',
      'SQLITE_NOTFOUND',
      'SQLITE_OPEN_CREATE',
      'SQLITE_OPEN_DELETEONCLOSE',
      'SQLITE_OPEN_MAIN_DB',
      'SQLITE_OPEN_READONLY'
    ].forEach((k)=>{
      if(undefined === (state.sq3Codes[k] = capi[k])){
        toss("Maintenance required: not found:",k);
      }
    });
    state.opfsFlags = Object.assign(Object.create(null),{
      /**
         Flag for use with xOpen(). "opfs-unlock-asap=1" enables
         this. See defaultUnlockAsap, below.
       */
      OPFS_UNLOCK_ASAP: 0x01,
      /**
         If true, any async routine which implicitly acquires a sync
         access handle (i.e. an OPFS lock) will release that locks at
         the end of the call which acquires it. If false, such
         "autolocks" are not released until the VFS is idle for some
         brief amount of time.

         The benefit of enabling this is much higher concurrency. The
         down-side is much-reduced performance (as much as a 4x decrease
         in speedtest1).
      */
      defaultUnlockAsap: false
    });

    /**
       Runs the given operation (by name) in the async worker
       counterpart, waits for its response, and returns the result
       which the async worker writes to SAB[state.opIds.rc]. The
       2nd and subsequent arguments must be the aruguments for the

           to encode them... TextEncoder can do that for us. */
        warn("OPFS xGetLastError() has nothing sensible to return.");
        return 0;
      },
      //xSleep is optionally defined below
      xOpen: function f(pVfs, zName, pFile, flags, pOutFlags){
        mTimeStart('xOpen');
        let opfsFlags = 0;
        if(0===zName){
          zName = randomFilename();
        }else if('number'===typeof zName){
          if(capi.sqlite3_uri_boolean(zName, "opfs-unlock-asap", 0)){
            /* -----------------------^^^^^ MUST pass the untranslated
               C-string here. */
            opfsFlags |= state.opfsFlags.OPFS_UNLOCK_ASAP;
          }
          zName = wasm.cstringToJs(zName);
        }
        const fh = Object.create(null);
        fh.fid = pFile;
        fh.filename = zName;
        fh.sab = new SharedArrayBuffer(state.fileBufferSize);
        fh.flags = flags;
        const rc = opRun('xOpen', pFile, zName, flags, opfsFlags);
        if(!rc){
          /* Recall that sqlite3_vfs::xClose() will be called, even on
             error, unless pFile->pMethods is NULL. */
          if(fh.readOnly){
            wasm.setMemValue(pOutFlags, capi.SQLITE_OPEN_READONLY, 'i32');
          }
          __openFiles[pFile] = fh;

        }
      };
      doDir(opt.directory, 0);
    };

    //TODO to support fiddle and worker1 db upload:
    //opfsUtil.createFile = function(absName, content=undefined){...}
    //We have sqlite3.wasm.sqlite3_wasm_vfs_create_file() for this
    //purpose but its interface and name are still under
    //consideration.

    if(sqlite3.oo1){
      opfsUtil.OpfsDb = function(...args){
        const opt = sqlite3.oo1.DB.dbCtorHelper.normalizeArgs(...args);
        opt.vfs = opfsVfs.$zName;
        sqlite3.oo1.DB.dbCtorHelper.call(this, opt);
      };

   metadata related to a given OPFS file handles. The pointers are, in
   this side of the interface, opaque file handle IDs provided by the
   synchronous part of this constellation. Each value is an object
   with a structure demonstrated in the xOpen() impl.
*/
const __openFiles = Object.create(null);
/**
   __implicitLocks is a Set of sqlite3_file pointers (integers) which were
   "auto-locked".  i.e. those for which we obtained a sync access
   handle without an explicit xLock() call. Such locks will be
   released during db connection idle time, whereas a sync access
   handle obtained via xLock(), or subsequently xLock()'d after
   auto-acquisition, will not be released until xUnlock() is called.

   Maintenance reminder: if we relinquish auto-locks at the end of the
   operation which acquires them, we pay a massive performance
   penalty: speedtest1 benchmarks take up to 4x as long. By delaying
   the lock release until idle time, the hit is negligible.
*/
const __implicitLocks = new Set();

/**
   Expects an OPFS file path. It gets resolved, such that ".."
   components are properly expanded, and returned. If the 2nd arg is
   true, the result is returned as an array of path elements, else an
   absolute path string is returned.
*/

*/
const closeSyncHandle = async (fh)=>{
  if(fh.syncHandle){
    log("Closing sync handle for",fh.filenameAbs);
    const h = fh.syncHandle;
    delete fh.syncHandle;
    delete fh.xLock;
    __implicitLocks.delete(fh.fid);
    return h.close();
  }
};

/**
   A proxy for closeSyncHandle() which is guaranteed to not throw.

  try{await closeSyncHandle(fh)}
  catch(e){
    warn("closeSyncHandleNoThrow() ignoring:",e,fh);
  }
};

/* Release all auto-locks. */
const releaseImplicitLocks = async ()=>{
  if(__implicitLocks.size){
    /* Release all auto-locks. */
    for(const fid of __implicitLocks){
      const fh = __openFiles[fid];
      await closeSyncHandleNoThrow(fh);
      log("Auto-unlocked",fid,fh.filenameAbs);
    }
  }
};

/**
   An experiment in improving concurrency by freeing up implicit locks
   sooner. This is known to impact performance dramatically but it has
   also shown to improve concurrency considerably.

   If fh.releaseImplicitLocks is truthy and fh is in __implicitLocks,
   this routine returns closeSyncHandleNoThrow(), else it is a no-op.
*/
const releaseImplicitLock = async (fh)=>{
  if(fh.releaseImplicitLocks && __implicitLocks.has(fh.fid)){
    return closeSyncHandleNoThrow(fh);
  }
};

/**
   An error class specifically for use with getSyncHandle(), the goal
   of which is to eventually be able to distinguish unambiguously
   between locking-related failures and other types, noting that we
   cannot currently do so because createSyncAccessHandle() does not
   define its exceptions in the required level of detail.

   In order to help alleviate cross-tab contention for a dabase,
   if an exception is thrown while acquiring the handle, this routine
   will wait briefly and try again, up to 3 times. If acquisition
   still fails at that point it will give up and propagate the
   exception.
*/
const getSyncHandle = async (fh,opName)=>{
  if(!fh.syncHandle){
    const t = performance.now();
    log("Acquiring sync handle for",fh.filenameAbs);
    const maxTries = 6, msBase = 300;
    let i = 1, ms = msBase;
    for(; true; ms = msBase * ++i){
      try {
        //if(i<3) toss("Just testing getSyncHandle() wait-and-retry.");
        //TODO? A config option which tells it to throw here
        //randomly every now and then, for testing purposes.
        fh.syncHandle = await fh.fileHandle.createSyncAccessHandle();
        break;
      }catch(e){
        if(i === maxTries){
          throw new GetSyncHandleError(
            e, "Error getting sync handle for",opName+"().",maxTries,
            "attempts failed.",fh.filenameAbs
          );
        }
        warn("Error getting sync handle for",opName+"(). Waiting",ms,
             "ms and trying again.",fh.filenameAbs,e);
        //await releaseImplicitLocks();
        Atomics.wait(state.sabOPView, state.opIds.retry, 0, ms);
      }
    }
    log("Got",opName+"() sync handle for",fh.filenameAbs,
        'in',performance.now() - t,'ms');
    if(!fh.xLock){
      __implicitLocks.add(fh.fid);
      log("Auto-locked for",opName+"()",fh.fid,fh.filenameAbs);
    }
  }
  return fh.syncHandle;
};

/**
   Stores the given value at state.sabOPView[state.opIds.rc] and then

    }
    storeAndNotify('xAccess', rc);
    mTimeEnd();
  },
  xClose: async function(fid/*sqlite3_file pointer*/){
    const opName = 'xClose';
    mTimeStart(opName);
    __implicitLocks.delete(fid);
    const fh = __openFiles[fid];
    let rc = 0;
    wTimeStart(opName);
    if(fh){
      delete __openFiles[fid];
      await closeSyncHandle(fh);
      if(fh.deleteOnClose){

  xFileSize: async function(fid/*sqlite3_file pointer*/){
    mTimeStart('xFileSize');
    const fh = __openFiles[fid];
    let rc;
    wTimeStart('xFileSize');
    try{
      affirmLocked('xFileSize',fh);
      const sz = await (await getSyncHandle(fh,'xFileSize')).getSize();
      state.s11n.serialize(Number(sz));
      rc = 0;
    }catch(e){
      state.s11n.storeException(2,e);
      rc = GetSyncHandleError.convertRc(e,state.sq3Codes.SQLITE_IOERR);
    }
    await releaseImplicitLock(fh);
    wTimeEnd();
    storeAndNotify('xFileSize', rc);
    mTimeEnd();
  },
  xLock: async function(fid/*sqlite3_file pointer*/,
                        lockType/*SQLITE_LOCK_...*/){
    mTimeStart('xLock');
    const fh = __openFiles[fid];
    let rc = 0;
    const oldLockType = fh.xLock;
    fh.xLock = lockType;
    if( !fh.syncHandle ){
      wTimeStart('xLock');
      try {
        await getSyncHandle(fh,'xLock');
        __implicitLocks.delete(fid);
      }catch(e){
        state.s11n.storeException(1,e);
        rc = GetSyncHandleError.convertRc(e,state.sq3Codes.SQLITE_IOERR_LOCK);
        fh.xLock = oldLockType;
      }
      wTimeEnd();
    }
    storeAndNotify('xLock',rc);
    mTimeEnd();
  },
  xOpen: async function(fid/*sqlite3_file pointer*/, filename,
                        flags/*SQLITE_OPEN_...*/,
                        opfsFlags/*OPFS_...*/){
    const opName = 'xOpen';
    mTimeStart(opName);

    const create = (state.sq3Codes.SQLITE_OPEN_CREATE & flags);
    wTimeStart('xOpen');
    try{
      let hDir, filenamePart;
      try {
        [hDir, filenamePart] = await getDirForFilename(filename, !!create);
      }catch(e){
        state.s11n.storeException(1,e);
        storeAndNotify(opName, state.sq3Codes.SQLITE_NOTFOUND);
        mTimeEnd();
        wTimeEnd();
        return;
      }
      const hFile = await hDir.getFileHandle(filenamePart, {create});






      wTimeEnd();
      const fh = Object.assign(Object.create(null),{
        fid: fid,
        filenameAbs: filename,
        filenamePart: filenamePart,
        dirHandle: hDir,
        fileHandle: hFile,
        sabView: state.sabFileBufView,
        readOnly: create
          ? false : (state.sq3Codes.SQLITE_OPEN_READONLY & flags),
        deleteOnClose: !!(state.sq3Codes.SQLITE_OPEN_DELETEONCLOSE & flags)
      });
      fh.releaseImplicitLocks =
        (opfsFlags & state.opfsFlags.OPFS_UNLOCK_ASAP)
        || state.opfsFlags.defaultUnlockAsap;
      if(0 /* this block is modelled after something wa-sqlite
              does but it leads to immediate contention on journal files. */
         && (0===(flags & state.sq3Codes.SQLITE_OPEN_MAIN_DB))){
        /* sqlite does not lock these files, so go ahead and grab an OPFS
           lock.

           https://www.sqlite.org/uri.html
        */
        fh.xLock = "xOpen"/* Truthy value to keep entry from getting
                             flagged as auto-locked. String value so
                             that we can easily distinguish is later
                             if needed. */;
        await getSyncHandle(fh,'xOpen');
      }
      __openFiles[fid] = fh;
      storeAndNotify(opName, 0);
    }catch(e){
      wTimeEnd();
      error(opName,e);
      state.s11n.storeException(1,e);
      storeAndNotify(opName, state.sq3Codes.SQLITE_IOERR);
    }
    mTimeEnd();
  },
  xRead: async function(fid/*sqlite3_file pointer*/,n,offset64){
    mTimeStart('xRead');
    let rc = 0, nRead;
    const fh = __openFiles[fid];
    try{
      affirmLocked('xRead',fh);
      wTimeStart('xRead');
      nRead = (await getSyncHandle(fh,'xRead')).read(
        fh.sabView.subarray(0, n),
        {at: Number(offset64)}
      );
      wTimeEnd();
      if(nRead < n){/* Zero-fill remaining bytes */
        fh.sabView.fill(0, nRead, n);
        rc = state.sq3Codes.SQLITE_IOERR_SHORT_READ;
      }
    }catch(e){
      if(undefined===nRead) wTimeEnd();
      error("xRead() failed",e,fh);
      state.s11n.storeException(1,e);
      rc = GetSyncHandleError.convertRc(e,state.sq3Codes.SQLITE_IOERR_READ);
    }
    await releaseImplicitLock(fh);
    storeAndNotify('xRead',rc);
    mTimeEnd();
  },
  xSync: async function(fid/*sqlite3_file pointer*/,flags/*ignored*/){
    mTimeStart('xSync');
    const fh = __openFiles[fid];
    let rc = 0;

    mTimeStart('xTruncate');
    let rc = 0;
    const fh = __openFiles[fid];
    wTimeStart('xTruncate');
    try{
      affirmLocked('xTruncate',fh);
      affirmNotRO('xTruncate', fh);
      await (await getSyncHandle(fh,'xTruncate')).truncate(size);
    }catch(e){
      error("xTruncate():",e,fh);
      state.s11n.storeException(2,e);
      rc = GetSyncHandleError.convertRc(e,state.sq3Codes.SQLITE_IOERR_TRUNCATE);
    }
    await releaseImplicitLock(fh);
    wTimeEnd();
    storeAndNotify('xTruncate',rc);
    mTimeEnd();
  },
  xUnlock: async function(fid/*sqlite3_file pointer*/,
                          lockType/*SQLITE_LOCK_...*/){
    mTimeStart('xUnlock');

    let rc;
    const fh = __openFiles[fid];
    wTimeStart('xWrite');
    try{
      affirmLocked('xWrite',fh);
      affirmNotRO('xWrite', fh);
      rc = (
        n === (await getSyncHandle(fh,'xWrite'))
          .write(fh.sabView.subarray(0, n),
                 {at: Number(offset64)})
      ) ? 0 : state.sq3Codes.SQLITE_IOERR_WRITE;
    }catch(e){
      error("xWrite():",e,fh);
      state.s11n.storeException(1,e);
      rc = GetSyncHandleError.convertRc(e,state.sq3Codes.SQLITE_IOERR_WRITE);
    }
    await releaseImplicitLock(fh);
    wTimeEnd();
    storeAndNotify('xWrite',rc);
    mTimeEnd();
  }
}/*vfsAsyncImpls*/;

const initS11n = ()=>{

  }
  /**
     waitTime is how long (ms) to wait for each Atomics.wait().
     We need to wake up periodically to give the thread a chance
     to do other things. If this is too high (e.g. 500ms) then
     even two workers/tabs can easily run into locking errors.
  */
  const waitTime = 100;
  while(!flagAsyncShutdown){
    try {
      if('timed-out'===Atomics.wait(
        state.sabOPView, state.opIds.whichOp, 0, waitTime
      )){
        await releaseImplicitLocks();
        continue;
      }
      const opId = Atomics.load(state.sabOPView, state.opIds.whichOp);
      Atomics.store(state.sabOPView, state.opIds.whichOp, 0);
      const hnd = opHandlers[opId] ?? toss("No waitLoop handler for whichOp #",opId);
      const args = state.s11n.deserialize(
        true /* clear s11n to keep the caller from confusing this with

          state.sabOP = opt.sabOP;
          state.sabOPView = new Int32Array(state.sabOP);
          state.sabIO = opt.sabIO;
          state.sabFileBufView = new Uint8Array(state.sabIO, 0, state.fileBufferSize);
          state.sabS11nView = new Uint8Array(state.sabIO, state.sabS11nOffset, state.sabS11nSize);
          state.opIds = opt.opIds;
          state.sq3Codes = opt.sq3Codes;
          state.opfsFlags = opt.opfsFlags;
          Object.keys(vfsAsyncImpls).forEach((k)=>{
            if(!Number.isFinite(state.opIds[k])){
              toss("Maintenance required: missing state.opIds[",k,"]");
            }
          });
          initS11n();
          metrics.reset();

      OPFS concurrency tester using multiple independent Workers.
      Disclaimer: concurrency in OPFS is currently a pain point
      and timing/concurrency mitigation in this environment is
      highly unpredictable!
    </p>
    <p>
      URL flags: pass a number of workers using
      the <code>workers=N</code> URL flag. Set the time between each
      workload with <code>interval=N</code> (milliseconds). Set the
      number of worker iterations with <code>iterations=N</code>.
      Enable OPFS VFS verbosity with <code>verbose=1-3</code> (output
      goes to the dev console). Enable/disable "unlock ASAP" mode
      (higher concurrency, lower speed)
      with <code>unlock-asap=0-1</code>.
    </p>
    <p>Achtung: if it does not start to do anything within a couple of
      seconds, check the dev console: Chrome often fails with "cannot allocate
      WasmMemory" at startup. Closing and re-opening the tab usually resolves
      it.
    </p>
    <div class='input-wrapper'>

  const urlArgsJs = new URL(document.currentScript.src).searchParams;
  const urlArgsHtml = new URL(self.location.href).searchParams;
  const options = Object.create(null);
  options.sqlite3Dir = urlArgsJs.get('sqlite3.dir');
  options.workerCount = (
    urlArgsHtml.has('workers') ? +urlArgsHtml.get('workers') : 3
  ) || 4;
  options.opfsVerbose = (
    urlArgsHtml.has('verbose') ? +urlArgsHtml.get('verbose') : 1
  ) || 1;
  options.interval = (
    urlArgsHtml.has('interval') ? +urlArgsHtml.get('interval') : 750
  ) || 1000;
  options.iterations = (
    urlArgsHtml.has('iterations') ? +urlArgsHtml.get('iterations') : 10
  ) || 10;
  options.unlockAsap = (
    urlArgsHtml.has('unlock-asap') ? +urlArgsHtml.get('unlock-asap') : 0
  ) || 0;
  const workers = [];
  workers.post = (type,...args)=>{
    for(const w of workers) w.postMessage({type, payload:args});
  };
  workers.counts = {loaded: 0, passed: 0, failed: 0};
  const checkFinished = function(){
    if(workers.counts.passed + workers.counts.failed !== workers.length){
      return;
    }
    if(workers.counts.failed>0){
      logCss('tests-fail',"Finished with",workers.counts.failed,"failure(s).");
    }else{
      logCss('tests-pass',"All",workers.length,"workers finished.");
    }
  };
  workers.onmessage = function(msg){
    msg = msg.data;
    const prefix = 'Worker #'+msg.worker+':';
    switch(msg.type){
        case 'loaded':
          stdout(prefix,"loaded");
          if(++workers.counts.loaded === workers.length){
            stdout("All",workers.length,"workers loaded. Telling them to run...");
            workers.post('run');
          }
          break;
        case 'stdout': stdout(prefix,...msg.payload); break;
        case 'stderr': stderr(prefix,...msg.payload); break;
        case 'error': stderr(prefix,"ERROR:",...msg.payload); break;
        case 'finished':
          ++workers.counts.passed;
          logCss('tests-pass',prefix,...msg.payload);
          checkFinished();
          break;
        case 'failed':
          ++workers.counts.failed;
          logCss('tests-fail',prefix,"FAILED:",...msg.payload);
          checkFinished();
          break;
        default: logCss('error',"Unhandled message type:",msg); break;
    }
  };

  stdout("Launching",options.workerCount,"workers. Options:",options);
  workers.uri = (
    'worker.js?'
      + 'sqlite3.dir='+options.sqlite3Dir
      + '&interval='+options.interval
      + '&iterations='+options.iterations
      + '&opfs-verbose='+options.opfsVerbose
      + '&opfs-unlock-asap='+options.unlockAsap
  );
  for(let i = 0; i < options.workerCount; ++i){
    stdout("Launching worker...");
    workers.push(new Worker(
      workers.uri+'&workerId='+(i+1)+(i ? '' : '&unlink-db')
    ));
  }

importScripts(
  (new URL(self.location.href).searchParams).get('sqlite3.dir') + '/sqlite3.js'
);
self.sqlite3InitModule().then(async function(sqlite3){
  const urlArgs = new URL(self.location.href).searchParams;
  const options = {
    workerName: urlArgs.get('workerId') || Math.round(Math.random()*10000),
    unlockAsap: urlArgs.get('opfs-unlock-asap') || 0 /*EXPERIMENTAL*/
  };
  const wPost = (type,...payload)=>{
    postMessage({type, worker: options.workerName, payload});
  };
  const stdout = (...args)=>wPost('stdout',...args);
  const stderr = (...args)=>wPost('stderr',...args);
  if(!sqlite3.opfs){
    stderr("OPFS support not detected. Aborting.");
    return;
  }

      wPost('failed',"Ending work after interval #"+interval.count,
            "due to error:",interval.error);
    }else{
      wPost('finished',"Ending work after",interval.count,"intervals.");
    }
  };
  const run = async function(){
    db = new sqlite3.opfs.OpfsDb({
      filename: 'file:'+dbName+'?opfs-unlock-asap='+options.unlockAsap,
      flags: 'c'
    });
    sqlite3.capi.sqlite3_busy_timeout(db.pointer, 5000);
    db.transaction((db)=>{
      db.exec([
        "create table if not exists t1(w TEXT UNIQUE ON CONFLICT REPLACE,v);",
        "create table if not exists t2(w TEXT UNIQUE ON CONFLICT REPLACE,v);"
      ]);
    });

    const maxIterations =
          urlArgs.has('iterations') ? (+urlArgs.get('iterations') || 10) : 10;
    stdout("Starting interval-based db updates with delay of",interval.delay,"ms.");
    const doWork = async ()=>{
      const tm = new Date().getTime();
      ++interval.count;
      const prefix = "v(#"+interval.count+")";
      stdout("Setting",prefix,"=",tm);
      try{
        db.exec({
          sql:"INSERT OR REPLACE INTO t1(w,v) VALUES(?,?)",
          bind: [options.workerName, new Date().getTime()]
        });
        //stdout("Set",prefix);
      }catch(e){
        interval.error = e;
      }
    };
    if(1){/*use setInterval()*/