// @tags: [
//   # Cannot implicitly shard accessed collections because of following errmsg: A single
//   # update/delete on a sharded collection must contain an exact match on _id or contain the shard
//   # key.
//   assumes_unsharded_collection,
//   # Uses $where operator
//   requires_scripting,
//   uses_multiple_connections,
//   uses_parallel_shell,
// ]

// Ensures that find and modify will not apply an update to a document which, due to a concurrent
// modification, no longer matches the query predicate.
(function() {
"use strict";

// Repeat the test a few times, as the timing of the yield means it won't fail consistently.
for (var i = 0; i < 3; i++) {
    var t = db.find_and_modify_concurrent;
    t.drop();

    assert.commandWorked(t.ensureIndex({a: 1}));
    assert.commandWorked(t.ensureIndex({b: 1}));
    assert.commandWorked(t.insert({_id: 1, a: 1, b: 1}));

    var join =
        startParallelShell("db.find_and_modify_concurrent.update({a: 1, b: 1}, {$inc: {a: 1}});");

    // Due to the sleep, we expect this find and modify to yield before updating the
    // document.
    var res = t.findAndModify(
        {query: {a: 1, b: 1, $where: "sleep(100); return true;"}, update: {$inc: {a: 1}}});

    join();
    var docs = t.find().toArray();
    assert.eq(docs.length, 1);

    // Both the find and modify and the update operations look for a document with a==1,
    // and then increment 'a' by 1. One should win the race and set a=2. The other should
    // fail to find a match. The assertion is that 'a' got incremented once (not zero times
    // and not twice).
    assert.eq(docs[0].a, 2);
}
})();