More thorough overlapping cursor tests.

third_party/WebKit/LayoutTests/external/wpt/IndexedDB/interleaved-cursors-support.js

+'use strict';
+
+// Size of large objects. This should exceed the size of a block in the storage
+// method underlying the browser's IndexedDB implementation. For example, this
+// needs to exceed the LevelDB block size on Chrome, and the SQLite block size
+// on Firefox.
+const largeObjectSize = 48 * 1024;
+
+function largeObjectValue(cursorIndex, itemIndex) {
+  // We use a typed array (as opposed to a string) because IndexedDB
+  // implementations may serialize strings using UTF-8 or UTF-16, yielding
+  // larger IndexedDB entries than we'd expect. It's very unlikely that an
+  // IndexedDB implementation would use anything other than the raw buffer to
+  // serialize a typed array.
+  const buffer = new Uint8Array(largeObjectSize);
+
+  // Some IndexedDB implementations, like LevelDB, compress their data blocks
+  // before storing them to disk. We use a simple 32-bit xorshift PRNG, which
+  // should be sufficient to foil any fast generic-purpose compression scheme.
+
+  // 32-bit xorshift - the seed can't be zero
+  let state = 1000 + (cursorIndex * itemCount + itemIndex);
+
+  for (let i = 0; i < largeObjectSize; ++i) {
+    state ^= state << 13;
+    state ^= state >> 17;
+    state ^= state << 5;
+    buffer[i] = state & 0xff;
+  }
+
+  return buffer;
+}
+
+// Writes the objects to be read by one cursor. Returns a promise that resolves
+// when the write completes.
+//
+// We want to avoid creating a large transaction, because that is outside the
+// test's scope, and it's a bad practice. So we break up the writes across
+// multiple transactions. For simplicity, each transaction writes all the
+// objects that will be read by a cursor.
+function writeCursorObjects(database, cursorIndex) {
+  return new Promise((resolve, reject) => {
+    const transaction = database.transaction('cache', 'readwrite');
+    transaction.onabort = () => { reject(transaction.error); };
+
+    const store = transaction.objectStore('cache');
+    for (let i = 0; i < itemCount; ++i) {
+      store.put({
+          key: objectKey(cursorIndex, i), value: objectValue(cursorIndex, i)});
+    }
+    transaction.oncomplete = resolve;
+  });
+}
+
+// Returns a promise that resolves when the store has been populated.
+function populateTestStore(testCase, database, cursorCount) {
+  let promiseChain = Promise.resolve();
+
+  for (let i = 0; i < cursorCount; ++i)
+    promiseChain = promiseChain.then(() => writeCursorObjects(database, i));
+
+  return promiseChain;
+}
+
+// A bank of cursors that can be used in an interleaved or parallel manner.
+class CursorBank {
+  constructor(testCase, store, cursorCount) {
+    this.testCase = testCase;
+    this.store = store;
+    this.itemCount = itemCount;
+
+    // The cursors used for iteration are stored here so each cursor's onsuccess
+    // handler can call continue() on the next cursor.
+    this.cursors = [];
+
+    // The results of IDBObjectStore.openCursor() calls are stored here so we
+    // we can change the requests' onsuccess handler after every
+    // IDBCursor.continue() call.
+    this.requests = [];
+  }
+
+  // Asserts that a cursor's key and value match the expectation.
+  checkCursorState(cursorIndex, itemIndex) {
+    this.testCase.step(() => {
+      const cursor = this.cursors[cursorIndex];
+
+      if (itemIndex < this.itemCount) {
+        assert_equals(cursor.key, objectKey(cursorIndex, itemIndex));
+        assert_equals(cursor.value.key, objectKey(cursorIndex, itemIndex));
+        assert_equals(
+            cursor.value.value.join('-'),
+            objectValue(cursorIndex, itemIndex).join('-'));
+      } else {
+        assert_equals(cursor, null);
+      }
+    });
+  }
+
+  // Opens a cursor. The callback is called when the cursor open succeeds.
+  openCursor(cursorIndex, callback) {
+    this.testCase.step(() => {
+      const request = this.store.openCursor(IDBKeyRange.bound(
+          objectKey(cursorIndex, 0), objectKey(cursorIndex, this.itemCount)));
+      this.requests[cursorIndex] = request;
+
+      request.onsuccess = this.testCase.step_func(() => {
+        const cursor = request.result;
+        this.cursors[cursorIndex] = cursor;
+        this.checkCursorState(cursorIndex, 0);
+        callback();
+      });
+      request.onerror = () => {
+        this.testCase.unreached_func(
+            `IDBObjectStore.openCursor failed: ${request.error}`);
+      };
+    });
+  }
+
+  // Reads the next item available in the cursor. The callback is called when
+  // the read suceeds.
+  continueCursor(cursorIndex, itemIndex, callback) {
+    this.testCase.step(() => {
+      const request = this.requests[cursorIndex];
+      request.onsuccess = this.testCase.step_func(() => {
+        const cursor = request.result;
+        this.cursors[cursorIndex] = cursor;
+        this.checkCursorState(cursorIndex, itemIndex);
+        callback();
+      });
+      request.onerror = this.testCase.unreached_func(
+          `IDBCursor.continue() failed: ${request.error}`);
+      request.onerror = () => {
+        this.testCase.unreached_func(
+            `IDBCursor.continue() failed: ${request.error}`);
+      };
+
+      const cursor = this.cursors[cursorIndex];
+      cursor.continue();
+    });
+  }
+}
+
+// Reads cursors in an interleaved fashion, as shown below. Returns a promise
+// that resolves when the reading is done.
+//
+// Given N cursors, each of which points to the beginning of a K-item sequence,
+// the following accesses will be made.
+//
+// OC(i)    = open cursor i
+// RD(i, j) = read result of cursor i, which should be at item j
+// REND(i)  = read result of cursor i, which should be at the end of items
+// CC(i)    = continue cursor i
+// |        = wait for onsuccess on the previous OC or CC
+//
+// OC(1)            | RD(1, 1) OC(2) | RD(2, 1) OC(3) | ... | RD(n-1, 1) CC(n) |
+// RD(n, 1)   CC(1) | RD(1, 2) CC(2) | RD(2, 2) CC(3) | ... | RD(n-1, 2) CC(n) |
+// RD(n, 2)   CC(1) | RD(1, 3) CC(2) | RD(2, 3) CC(3) | ... | RD(n-1, 3) CC(n) |
+// ...
+// RD(n, k-1) CC(1) | RD(1, k) CC(2) | RD(2, k) CC(3) | ... | RD(n-1, k) CC(n) |
+// RD(n)      CC(1) | REND(1)  CC(2) | REND(2)  CC(3) | ... | REND(n-1)  CC(n) |
+// REND(n)            done
+function interleaveCursors(testCase, store, cursorCount, itemCount) {
+  return new Promise((resolve, reject) => {
+    const cursors = new CursorBank(testCase, store, itemCount);
+
+    // We open all the cursors one at a time, then cycle through the cursors and
+    // call continue() on each of them. This access pattern causes maximal
+    // trashing to an LRU cursor cache. Eviction scheme aside, any cache will
+    // have to evict some cursors, and this access pattern verifies that the
+    // cache correctly restores the state of evicted cursors.
+    const steps = [];
+    for (let cursorIndex = 0; cursorIndex < cursorCount; ++cursorIndex)
+      steps.push(cursors.openCursor.bind(cursors, cursorIndex));
+    for (let itemIndex = 1; itemIndex <= itemCount; ++itemIndex) {
+      for (let cursorIndex = 0; cursorIndex < cursorCount; ++cursorIndex) {
+        steps.push(
+            cursors.continueCursor.bind(cursors, cursorIndex, itemIndex));
+      }
+    }
+
+    const runStep = (stepIndex) => {
+      if (stepIndex === steps.length) {
+        resolve();
+        return;
+      }
+      steps[stepIndex](testCase.step_func(() => { runStep(stepIndex + 1); }));
+    };
+    runStep(0);
+  });
+}