stringbuffer-6.js - mozsearch

// Test that long strings allocated by rope flattening have a string buffer.

gczeal(0);

// Must match sizeof(mozilla::StringBuffer)

const StringBufferSizeInBytes = 8;

function checkRefCount(s, expected) {

    // stringRepresentation and the bufferRefCount field aren't available in

    // all builds.

    if (getBuildConfiguration("debug")) {

        finishBackgroundFree();

        var repr = JSON.parse(stringRepresentation(s));

        assertEq(repr.bufferRefCount, expected);

function checkExtensibleCapacity(s, expected) {

    if (getBuildConfiguration("debug")) {

        var repr = JSON.parse(stringRepresentation(s));

        assertEq(repr.capacity, expected);

function testBasicLatin1() {

    var s1 = ensureLinearString("a".repeat(1000));

    var s2 = ensureLinearString("b".repeat(1000));

    var flattened1 = ensureLinearString(newRope(s1, s2));

    checkRefCount(flattened1, 1);

    // Test that the string's capacity + StringBuffer + null terminator fills up

    // a jemalloc bucket of 2048 bytes.

    var expectedCapacity = 2048 - StringBufferSizeInBytes - 1 /* null terminator */;

    checkExtensibleCapacity(flattened1, expectedCapacity);

    // Move string buffer to flattened2 and turn flattened into a dependent string.

    var flattened2 = ensureLinearString(flattened1 + "abcdef");

    checkRefCount(flattened1, undefined);

    checkRefCount(flattened2, 1);

    assertEq(flattened2.length, 2006);

    // Share the StringBuffer with another JS string.

    var sharedBuffer = newString(flattened2, {shareStringBuffer: true});

    checkRefCount(flattened2, 2);

    // Because there are now multiple references, we don't use the extensible buffer.

    var flattened3 = ensureLinearString(flattened2 + "abcdef");

    checkRefCount(flattened2, 2);

    checkRefCount(flattened3, 1);

    checkExtensibleCapacity(flattened3, expectedCapacity);

testBasicLatin1();

function testBasicTwoByte() {

    var s1 = ensureLinearString("\u1234".repeat(500));

    var s2 = ensureLinearString("\u1256".repeat(500));

    var flattened1 = ensureLinearString(newRope(s1, s2));

    checkRefCount(flattened1, 1);

    // Test that the string's capacity + StringBuffer + null terminator fills up

    // a jemalloc bucket of 2048 bytes.

    var expectedCapacity = 1024 - StringBufferSizeInBytes / 2 - 1 /* null terminator */;

    checkExtensibleCapacity(flattened1, expectedCapacity);

    // Move string buffer to flattened2 and turn flattened into a dependent string.

    var flattened2 = ensureLinearString(flattened1 + "abcdef");

    checkRefCount(flattened1, undefined);

    checkRefCount(flattened2, 1);

    assertEq(flattened2.length, 1006);

    // Share the StringBuffer with another JS string.

    var sharedBuffer = newString(flattened2, {shareStringBuffer: true});

    checkRefCount(flattened2, 2);

    // Because there are now multiple references, we don't use the extensible buffer.

    var flattened3 = ensureLinearString(flattened2 + "abcdef");

    checkRefCount(flattened2, 2);

    checkRefCount(flattened3, 1);

    checkExtensibleCapacity(flattened3, expectedCapacity);

testBasicTwoByte();

function testBufferTransfer(fromNursery, toNursery) {

    var s1 = ensureLinearString("a".repeat(1000));

    var s2 = ensureLinearString("b".repeat(1000));

    var flattened1 = ensureLinearString(newRope(s1, s2, {nursery: fromNursery}));

    checkRefCount(flattened1, 1);

    var flattened2 = ensureLinearString(newRope(flattened1, "abcdef", {nursery: toNursery}));

    checkRefCount(flattened1, undefined);

    checkRefCount(flattened2, 1);

    gc();

    checkRefCount(flattened2, 1);

testBufferTransfer(false, false);

testBufferTransfer(false, true);

testBufferTransfer(true, false);

testBufferTransfer(true, true);