Add a small test app demonstrating cooperative semi-concurrency of the opfs-sahpool VFS using its un/pauseVfs() APIs.

FossilOrigin-Name: 09570c55a23e5af76dd2153a5b28a493f498d7d4a08b0089f3074d0a2c5d3d29

ext/wasm/tests/opfs/sahpool/sahpool-worker.js

@@ -0,0 +1,89 @@
+const searchParams = new URL(self.location.href).searchParams;
+const workerId = searchParams.get('workerId');
+const wPost = (type,...args)=>postMessage({type, workerId, payload:args});
+const log = (...args)=>wPost('log',...args);
+let capi, wasm, S, poolUtil;
+
+const sahPoolConfig = {
+  name: 'opfs-sahpool-pausable',
+  clearOnInit: false,
+  initialCapacity: 3
+};
+
+importScripts(searchParams.get('sqlite3.dir') + '/sqlite3.js');
+
+const sqlExec = function(sql){
+  const db = new poolUtil.OpfsSAHPoolDb('/my.db');
+  try{
+    return db.exec(sql);
+  }finally{
+    db.close();
+  }
+};
+
+const clog = console.log.bind(console);
+globalThis.onmessage = function({data}){
+  clog(workerId+": onmessage:",data);
+  switch(data.type){
+    case 'vfs-acquire':
+      if( poolUtil ){
+        poolUtil.unpauseVfs().then(()=>wPost('vfs-unpaused'));
+      }else{
+        S.installOpfsSAHPoolVfs(sahPoolConfig).then(pu=>{
+          poolUtil = pu;
+          wPost('vfs-acquired');
+        });
+      }
+      break;
+    case 'db-init':
+      try{
+        sqlExec([
+          "DROP TABLE IF EXISTS mytable;",
+          "CREATE TABLE mytable(a);",
+          "INSERT INTO mytable(a) VALUES(11),(22),(33)"
+        ]);
+        wPost('db-inited');
+      }catch(e){
+        wPost('error',e.message);
+      }
+      break;
+    case 'db-query': {
+      const rc = sqlExec({
+        sql: 'select * from mytable order by a',
+        rowMode: 'array',
+        returnValue: 'resultRows'
+      });
+      wPost('query-result',rc);
+      break;
+    }
+    case 'vfs-remove':
+      poolUtil.removeVfs().then(()=>wPost('vfs-removed'));
+      break;
+    case 'vfs-pause':
+      poolUtil.pauseVfs();
+      wPost('vfs-paused');
+      break;
+  }
+};
+
+const hasOpfs = ()=>{
+  return globalThis.FileSystemHandle
+    && globalThis.FileSystemDirectoryHandle
+    && globalThis.FileSystemFileHandle
+    && globalThis.FileSystemFileHandle.prototype.createSyncAccessHandle
+    && navigator?.storage?.getDirectory;
+};
+if( !hasOpfs() ){
+  wPost('error',"OPFS not detected");
+}else{
+  globalThis.sqlite3InitModule().then(async function(sqlite3){
+    S = sqlite3;
+    capi = S.capi;
+    wasm = S.wasm;
+    log("sqlite3 version:",capi.sqlite3_libversion(),
+        capi.sqlite3_sourceid());
+    //return sqlite3.installOpfsSAHPoolVfs(sahPoolConfig).then(pu=>poolUtil=pu);
+  }).then(()=>{
+    wPost('initialized');
+  });
+}