Loop Download

Remember: All the template tags rely on the $post global variable by default and the $post global variable is set/modified by the_post(), which gets its data from the $wp_query global variable. $post is also set/modified by WP_Query::the_post() as used in secondary loops.

First off, why would one want to use multiple loops? In general, the answer is that you might want to do something with one group of posts, and do something different to another group of posts, but display both groups on the same page. "Something" could mean almost anything; you are only limited by your PHP skill and your imagination.

Loop Download

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An explanation for the coders out there:The have_posts() and the_post() are convenience wrappers around the global $wp_query object, which is where all of the action is. The $wp_query is called in the blog header and fed query arguments coming in through GET and PATH_INFO. The $wp_query takes the arguments and builds and executes a DB query that results in an array of posts. This array is stored in the object and also returned back to the blog header where it is stuffed into the global $posts array (for backward compatibility with old post loops).

Once WordPress has finished loading the blog header and is descending into the template, we arrive at our post Loop. The have_posts() simply calls into $wp_query->have_posts() which checks a loop counter to see if there are any posts left in the post array. And the_post() calls $wp_query->the_post() which advances the loop counter and sets up the global $post variable as well as all of the global post data. Once we have exhausted the loop, have_posts() will return false and we are done.

If you are finished with the posts in the original query, and you want to use a different query, you can reuse the $wp_query object by calling query_posts() and then looping back through. The query_posts() will perform a new query, build a new posts array, and reset the loop counter.

The best way to understand how to use multiple loops is to actually show an example of its use. Perhaps the most common use of multiple loops is to show two (or more) lists of posts on one page. This is often done when a webmaster wants to feature not only the very latest post written, but also posts from a certain category.

If posts_per_page=2 or more, you will need to alter the code a bit. The variable $do_not_duplicate needs to be changed into an array as opposed to a single value. Otherwise, the first loop will finish and the variable $do_not_duplicate will equal only the id of the latest post. This will result in duplicated posts in the second loop. To fix the problem replace

The section on multiple loops is a combination of Ryan Boren and Alex King's discussion about the Loop on the Hackers Mailing List. The nested loops example was inspired by another discussion on the mailing list and a post by Nicolas Kuttler.

After creating a setup() function, which initializes and sets the initial values, the loop() function does precisely what its name suggests, and loops consecutively, allowing your program to change and respond. Use it to actively control the Arduino board.

When Node.js starts, it initializes the event loop, processes theprovided input script (or drops into the REPL, which is not covered inthis document) which may make async API calls, schedule timers, or callprocess.nextTick(), then begins processing the event loop.

Each phase has a FIFO queue of callbacks to execute. While each phase isspecial in its own way, generally, when the event loop enters a givenphase, it will perform any operations specific to that phase, thenexecute callbacks in that phase's queue until the queue has beenexhausted or the maximum number of callbacks has executed. When thequeue has been exhausted or the callback limit is reached, the eventloop will move to the next phase, and so on.

When the event loop enters the poll phase, it has an empty queue(fs.readFile() has not completed), so it will wait for the number of msremaining until the soonest timer's threshold is reached. While it iswaiting 95 ms pass, fs.readFile() finishes reading the file and itscallback which takes 10 ms to complete is added to the poll queue andexecuted. When the callback finishes, there are no more callbacks in thequeue, so the event loop will see that the threshold of the soonesttimer has been reached then wrap back to the timers phase to executethe timer's callback. In this example, you will see that the total delaybetween the timer being scheduled and its callback being executed willbe 105ms.

To prevent the poll phase from starving the event loop, libuv(the C library that implements the Node.jsevent loop and all of the asynchronous behaviors of the platform)also has a hard maximum (system dependent) before it stops polling formore events.

If the poll queue is not empty, the event loop will iteratethrough its queue of callbacks executing them synchronously untileither the queue has been exhausted, or the system-dependent hard limitis reached.

Once the poll queue is empty the event loop will check for timerswhose time thresholds have been reached. If one or more timers areready, the event loop will wrap back to the timers phase to executethose timers' callbacks.

This phase allows a person to execute callbacks immediately after thepoll phase has completed. If the poll phase becomes idle andscripts have been queued with setImmediate(), the event loop maycontinue to the check phase rather than waiting.

Generally, as the code is executed, the event loop will eventually hitthe poll phase where it will wait for an incoming connection, request,etc. However, if a callback has been scheduled with setImmediate()and the poll phase becomes idle, it will end and continue to thecheck phase rather than waiting for poll events.

You may have noticed that process.nextTick() was not displayed in thediagram, even though it's a part of the asynchronous API. This is becauseprocess.nextTick() is not technically part of the event loop. Instead,the nextTickQueue will be processed after the current operation iscompleted, regardless of the current phase of the event loop. Here,an operation is defined as a transition from theunderlying C/C++ handler, and handling the JavaScript that needs to beexecuted.

Looking back at our diagram, any time you call process.nextTick() in agiven phase, all callbacks passed to process.nextTick() will beresolved before the event loop continues. This can create some badsituations because it allows you to "starve" your I/O by makingrecursive process.nextTick() calls, which prevents the event loopfrom reaching the poll phase.

What we're doing is passing an error back to the user but only afterwe have allowed the rest of the user's code to execute. By usingprocess.nextTick() we guarantee that apiCall() always runs itscallback after the rest of the user's code and before the event loopis allowed to proceed. To achieve this, the JS call stack is allowed tounwind then immediately execute the provided callback which allows aperson to make recursive calls to process.nextTick() without reaching aRangeError: Maximum call stack size exceeded from v8.

The user defines someAsyncApiCall() to have an asynchronous signature,but it actually operates synchronously. When it is called, the callbackprovided to someAsyncApiCall() is called in the same phase of theevent loop because someAsyncApiCall() doesn't actually do anythingasynchronously. As a result, the callback tries to reference bar eventhough it may not have that variable in scope yet, because the script has notbeen able to run to completion.

By placing the callback in a process.nextTick(), the script still has theability to run to completion, allowing all the variables, functions,etc., to be initialized prior to the callback being called. It also hasthe advantage of not allowing the event loop to continue. It may beuseful for the user to be alerted to an error before the event loop isallowed to continue. Here is the previous example using process.nextTick():

Say that listen() is run at the beginning of the event loop, but thelistening callback is placed in a setImmediate(). Unless ahostname is passed, binding to the port will happen immediately. Forthe event loop to proceed, it must hit the poll phase, which meansthere is a non-zero chance that a connection could have been receivedallowing the connection event to be fired before the listening event.

The Loop should be placed in index.php, and in any other templates which are used to display post information. Because you do not want to duplicate your header over and over, the loop should always be placed after the call to get_header(). For example:

Using two loops with the same query was relatively easy but not always what you will need. Instead, you will often want to create a secondary query to display different content on the template. For example, you might want to display two groups of posts on the same page, but do different things to each group. A common example of this, as shown below, is displaying a single post with a list of posts from the same category below the single post.

Note that the regular loop in the example above has one difference: it calls wp_reset_postdata() to reset the post data. Before you can use a second loop, you need to reset the post data. There are two ways to do this:

Ansible offers the loop, with_, and until keywords to execute a task multiple times. Examples of commonly-used loops include changing ownership on several files and/or directories with the file module, creating multiple users with the user module, andrepeating a polling step until a certain result is reached.

Be careful when changing with_items to loop, as with_items performed implicit single-level flattening. You may need to use flatten(1) with loop to match the exact outcome. For example, to get the same output as: ff782bc1db