Child process hangging on exit() call

chdir(__DIR__);

require_once __DIR__ . '/../vendor/autoload.php';

use \Couchbase\ClusterOptions;

use \Couchbase\Cluster;

$username         = 'user';

$password         = 'password';

$connectionString = 'couchbase://10.10.10.10';

$bucketName       = 'testing';

$scopeName        = '_default';

$collectionName   = '_default';

$clusterOpts = new ClusterOptions();

$clusterOpts->credentials($username, $password);

$couchbase  = new Cluster($connectionString. '?ppid=' . posix_getppid(), $clusterOpts);

$bucket     = $couchbase->bucket($bucketName);

$scope      = $bucket->scope($scopeName);

$collection = $scope->collection($collectionName);

$result = $collection->upsert('test-key', [time(), 'some data']);

$data = $collection->get('test-key')->content();

print_r($data);

$processId = pcntl_fork();

if ($processId < 0) {

    // cleanup using posix_kill & pcntl_wait

    throw new RuntimeException('pcntl_fork failed.');

} elseif ($processId === 0) {

    $couchbase  = new Cluster($connectionString. '?ppid=' . posix_getppid(), $clusterOpts);

    $bucket     = $couchbase->bucket($bucketName);

    $scope      = $bucket->scope($scopeName);

    $collection = $scope->collection($collectionName);

    $data = $collection->get('test-key')->content();

    print_r($data);

    exit(); // <-- locks up and never exits

} else {

    pcntl_wait($status);

    // WE ARE IN THE PARENT

    echo "parent\r\n";

}