mysqli::poll

    mysqli_poll

    (PHP 5 >= 5.3.0, PHP 7, PHP 8)

    mysqli::poll -- mysqli_poll — Poll connections

    Description

    Object-oriented style

    public static mysqli::poll(
        ?array &$read,
        ?array &$error,
        array &$reject,
        int $seconds,
        int $microseconds = 0
    ): int|false

    Procedural style

    mysqli_poll(
        ?array &$read,
        ?array &$error,
        array &$reject,
        int $seconds,
        int $microseconds = 0
    ): int|false

    Poll connections. The method can be used as static.

    Note:

    Available only with mysqlnd.

    Parameters

    read

    List of connections to check for outstanding results that can be read.

    error

    List of connections on which an error occurred, for example, query failure or lost connection.

    reject

    List of connections rejected because no asynchronous query has been run on for which the function could poll results.

    seconds

    Maximum number of seconds to wait, must be non-negative.

    microseconds

    Maximum number of microseconds to wait, must be non-negative.

    Return Values

    Returns number of ready connections upon success, false otherwise.

    Errors/Exceptions

    A ValueError is thrown when neither the read nor error arguments are passed.

    Changelog

    Version Description
    8.3.0 Now throws a ValueError exception when neither the read nor error arguments are passed.

    Examples

    Example #1 A mysqli_poll() example

    <?php
    $link1     = mysqli_connect();
    $link1->query("SELECT 'test'", MYSQLI_ASYNC);
    $all_links = array($link1);
    $processed = 0;
    do {
    $links = $errors = $reject = array();
    foreach (    $all_links as $link) {
    $links[] = $errors[] = $reject[] = $link;
    }
    if (!    mysqli_poll($links, $errors, $reject, 1)) {
    continue;
    }
    foreach (    $links as $link) {
    if (    $result = $link->reap_async_query()) {
    print_r($result->fetch_row());
    if (    is_object($result))
    mysqli_free_result($result);
    } else die(    sprintf("MySQLi Error: %s", mysqli_error($link)));
    $processed++;
    }
    } while (    $processed < count($all_links));
    ?>

    The above example will output:

    Array
(
    [0] => test
)

    See Also

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    User Contributed Notes 5 notes

    up
    7
    l_sanczyk at hotmail dot com
    10 years ago
    You can use the following code to execute, for example, 10 simultaneous queries:

    $query = "SELECT `field1`, `field2` FROM `table` WHERE `field1`='something'";

    $all_links = array();
    for($i=0; $i<10; $i++) {
    $link = mysqli_connect("your.mysql.server.here","your@user","pa$$w0rd",DataBase_Name");
    $link->query($query, MYSQLI_ASYNC);
    $all_links[] = $link;
    }

    $processed = 0;
    do {
    $links = $errors = $reject = array();
    foreach ($all_links as $link) {
    $links[] = $errors[] = $reject[] = $link;
    }
    if (!mysqli_poll($links, $errors, $reject, 1)) {
    continue;
    }
    foreach ($links as $link) {
    if ($result = $link->reap_async_query()) {
    print_r($result->fetch_row());
    if (is_object($result))
    mysqli_free_result($result);
    } else die(sprintf("MySQLi Error: %s", mysqli_error($link)));
    $processed++;
    }
    } while ($processed < count($all_links));

    NOTE: If you get a "Warning: mysqli::query() expects parameter 2 to be long, string given" you have a mysqlnd installation or configuration issue.
    up
    3
    shestero at meta dot ua
    8 years ago
    Sometime it's not clear what does it mean as connection is "ready" . Does it mean the query completed or just some records ready to read?
    Is it possible to use asynchronous (unblocking) and unbuffered SELECT-query? I.e. with both MYSQLI_ASYNC|MYSQLI_USE_RESULT

    I want some poll-like code inside my loop that has four case-options:
    1. Poll wait time-out is over but no records of result set is ready.
    2. One or more records are ready to read (but the query still running).
    3. Query is successfully over (completed; no more records).
    4. Error.

    Is it possible?

    As I understood the operation of reading a record from unbuffered query is blocking if there are no ready records at the moment, and there is no functions to get out how much records are ready ?
    up
    1
    marcin dot wanat at gmail dot com
    1 year ago
    It is worth to note that example from this docs will results in waiting for all queries to be executed before you can reap your results.

    5 years ago bishop from php.net has posted solution that allow to fetch results of each query immediately after executed. For some reason this has never been merged to php manual.

    https://bugs.php.net/bug.php?id=70505

    The documentation for mysqli_poll suggests iterating through the links after running the poll:

    foreach ($links as $link) {
    if ($result = $link->reap_async_query()) {
    print_r($result->fetch_row());
    if (is_object($result))
    mysqli_free_result($result);
    } else die(sprintf("MySQLi Error: %s", mysqli_error($link)));
    $processed++;
    }

    This is not a good way to go about it when you have queries of different run-times, because mysqli_reap_async_query() blocks until the query resolves, which is contrary to the nature of the async poll.

    An approach that respects multiple queries of different run times is to run a reaping function over each of the modified arrays:

    $count = mysqli_poll($read, $error, $reject, 1);
    if (0 < $count) {
    array_walk($read, 'reap');
    array_walk($error, 'reap');
    array_walk($reject, 'reap');
    }

    function reap($link) {
    $result = mysqli_reap_async_query($link);
    if (is_object($result)) {
    print_r($result->fetch_assoc()));
    mysqli_free_result($result);
    } else if (false !== $result) {
    print_r($link);
    } else {
    die(mysqli_error($link));
    }
    }

    This also handles the case where the query is a CRUD and the result of reap_async_query isn't a result object.
    up
    0
    ekalashnikov at gmail dot com
    7 years ago
    Improved version of using polling to check for slow query,
    "KILL #ID" does not work if id of the myqsli link is the same as the one that kills it,
    so you have to disconnect from mysqli and connect again with new link to
    kill the #ID.
    <?php
    // Slow SQL Query
    $SelectSql = 'SELECT * FROM SLOW_QUERY';
    $link = mysqli_connect('localhost','user','pass','database');
    mysqli_query($SelectSql, MYSQLI_ASYNC);
    $thread_id = mysqli_thread_id($link);
    // Ignore user abort so we can kill the query
    ignore_user_abort(true);
    $MaxTime = 5; // seconds
    $Overtime = false;
    $StartTime = time();
    do
    {
    // Poll MySQL
    $links = $errors = $reject = array($link);
    $poll = mysqli_poll($links, $errors, $reject, 0, 500000);
    // Check if the connection is aborted and the query was killed
    if (connection_aborted()) {
    $link_new = mysqli_connect('localhost','user','pass','database');
    mysqli_kill($link_new, $thread_id);
    $kill = mysqli_kill($link_new, $thread_id);
    if (    $kill)
    {
    die();
    }
    }
    $EndTime = time();
    // Check overtime, kill if detected overtime
    if ($EndTime - $StartTime > $MaxTime)
    {
    $link_new = mysqli_connect('localhost','user','pass','database');
    mysqli_kill($link_new, $thread_id);
    $Overtime = true;
    echo     'Error: Query took over '.$Overtime.'.';
    }
    } while (!    $poll && $Overtime == false);
    ?>
    up
    0
    ekalashnikov at gmail dot com
    7 years ago
    This is how you can test and terminate slow query with polling.

    <?php
    // Slow SQL Query
    $SelectSql = 'SELECT * FROM SLOW_QUERY';
    $link = mysqli_connect('localhost','user','pass','database');
    mysqli_query($SelectSql, MYSQLI_ASYNC);
    $thread_id = mysqli_thread_id($link);
    // Ignore user abort so we can kill the query
    ignore_user_abort(true);
    $MaxTime = 5; // seconds
    $Overtime = false;
    $StartTime = time();
    do
    {
    // Poll MySQL
    $links = $errors = $reject = array($link);
    $poll = mysqli_poll($links, $errors, $reject, 0, 500000);
    // Check if the connection is aborted and the query was killed
    if (connection_aborted() && mysqli_kill($link, $thread_id)) {
    die();
    }
    $EndTime = time();
    // Check overtime, kill if detected overtime
    if ($EndTime - $StartTime > $MaxTime)
    {
    mysqli_kill($link, $thread_id);
    $Overtime = true;
    echo     'Error: Query took over '.$Overtime.'.';
    }
    } while (!    $poll && $Overtime == false);
    ?>
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