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FutureIterator.php
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Mon, Mar 10, 08:39

FutureIterator.php
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<?php
/*
* Copyright 2011 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* @group futures
*/
function Futures($futures) {
return new FutureIterator($futures);
}
/**
* FutureIterator aggregates @{class:Future}s and allows you to respond to them
* in the order they resolve. This is useful because it minimizes the amount of
* time your program spends waiting on parallel processes.
*
* $futures = array(
* 'a.txt' => new ExecFuture('wc -c a.txt'),
* 'b.txt' => new ExecFuture('wc -c b.txt'),
* 'c.txt' => new ExecFuture('wc -c c.txt'),
* );
* foreach (Futures($futures) as $key => $future) {
* // IMPORTANT: keys are preserved but the order of elements is not. This
* // construct iterates over the futures in the order they resolve, so the
* // fastest future is the one you'll get first. This allows you to start
* // doing followup processing as soon as possible.
*
* list($stdout) = $future->resolvex();
* do_some_processing($stdout);
* }
*
* @group futures
*/
class FutureIterator implements Iterator {
protected $wait = array();
protected $work = array();
protected $futures = array();
protected $key;
protected $limit;
protected $timeout;
protected $isTimeout = false;
public function __construct(array $futures) {
foreach ($futures as $future) {
if (!$future instanceof Future) {
throw new Exception('Futures must all be objects implementing Future.');
}
}
$this->futures = $futures;
}
/**
* Set a maximum amount of time you want to wait before the iterator will
* yield a result. If no future has resolved yet, the iterator will yield
* null for key and value. Among other potential uses, you can use this to
* show some busy indicator:
*
* foreach (Futures($futures)->setUpdateInterval(1) as $future) {
* if ($future === null) {
* echo "Still working...\n";
* } else {
* // ...
* }
* }
*
* This will echo "Still working..." once per second as long as futures are
* resolving. By default, FutureIterator never yields null.
*
* @param float Maximum number of seconds to block waiting on futures before
* yielding null.
* @return this
*/
public function setUpdateInterval($interval) {
$this->timeout = $interval;
return $this;
}
public function rewind() {
$this->wait = array_keys($this->futures);
$this->work = null;
$this->updateWorkingSet();
$this->next();
}
protected function getWorkingSet() {
if ($this->work === null) {
return $this->wait;
}
return $this->work;
}
protected function updateWorkingSet() {
if (!$this->limit) {
$this->work = null;
}
$old = $this->work;
$this->work = array_slice($this->wait, 0, $this->limit, true);
// If we're using a limit, our futures are sleeping and need to be polled
// to begin execution, so poll any futures which weren't in our working set
// before.
foreach ($this->work as $work => $key) {
if (!isset($old[$work])) {
$this->futures[$key]->isReady();
}
}
}
public function next() {
$this->key = null;
if (!count($this->wait)) {
return;
}
$read_sokcets = array();
$write_sockets = array();
$start = microtime(true);
$wait_time = 1;
$timeout = $this->timeout;
$this->isTimeout = false;
$check = $this->getWorkingSet();
$resolve = null;
do {
$read_sockets = array();
$write_sockets = array();
$can_use_sockets = true;
foreach ($check as $wait => $key) {
$future = $this->futures[$key];
try {
if ($future->getException()) {
$resolve = $wait;
continue;
}
if ($future->isReady()) {
if ($resolve === null) {
$resolve = $wait;
}
continue;
}
$got_sockets = false;
$socks = $future->getReadSockets();
if ($socks) {
$got_sockets = true;
foreach ($socks as $socket) {
$read_sockets[] = $socket;
}
}
$socks = $future->getWriteSockets();
if ($socks) {
$got_sockets = true;
foreach ($socks as $socket) {
$write_sockets[] = $socket;
}
}
// If any currently active future had neither read nor write sockets,
// we can't wait for the current batch of items using sockets.
if (!$got_sockets) {
$can_use_sockets = false;
}
} catch (Exception $ex) {
$this->futures[$key]->setException($ex);
$resolve = $wait;
break;
}
}
if ($resolve === null) {
if ($can_use_sockets) {
if ($timeout !== null) {
$elapsed = microtime(true) - $start;
if ($elapsed > $timeout) {
$this->isTimeout = true;
return;
} else {
$wait_time = $timeout - $elapsed;
}
}
Future::waitForSockets($read_sockets, $write_sockets, $wait_time);
} else {
usleep(1000);
}
}
} while ($resolve === null);
$this->key = $this->wait[$resolve];
unset($this->wait[$resolve]);
$this->updateWorkingSet();
}
public function current() {
if ($this->isTimeout) {
return null;
}
return $this->futures[$this->key];
}
public function key() {
if ($this->isTimeout) {
return null;
}
return $this->key;
}
public function valid() {
if ($this->isTimeout) {
return true;
}
return ($this->key !== null);
}
public function resolveAll() {
foreach ($this as $_) {
// This implicitly forces all the futures to resolve.
}
}
/**
* Limits the number of simultaneous tasks.
*
* @param int Maximum number of simultaneous jobs allowed.
* @return this
*/
public function limit($max) {
$this->limit = $max;
return $this;
}
}

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