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Add lock function #34

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Add lock function #34

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0aebb80
Add lock function
danog Jul 15, 2019
c81957b
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danog Aug 22, 2019
0b7831d
Fixes
danog Aug 22, 2019
6ecb393
Return Lock
danog Aug 22, 2019
a76abf9
Improved description
danog Aug 22, 2019
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3 changes: 2 additions & 1 deletion composer.json
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Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,8 @@
"require": {
"amphp/amp": "^2",
"amphp/byte-stream": "^1",
"amphp/parallel": "^1"
"amphp/parallel": "^1",
"amphp/sync": "^1.0"
},
"require-dev": {
"amphp/phpunit-util": "^1",
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21 changes: 13 additions & 8 deletions lib/functions.php
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Expand Up @@ -7,6 +7,8 @@
use Amp\Loop;
use Amp\NullCancellationToken;
use Amp\Promise;
use Amp\Sync\Lock;

use function Amp\call;

const LOOP_STATE_IDENTIFIER = Driver::class;
Expand Down Expand Up @@ -364,7 +366,7 @@ function put(string $path, string $contents): Promise
* @param integer $polling Polling interval for lock in milliseconds
* @param CancellationToken $token Cancellation token
*
* @return \Amp\Promise Resolves with a callable that MUST eventually be called in order to release the lock.
* @return \Amp\Promise Resolves with a \Amp\Sync\Lock that MUST eventually be released
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*/
function lock(string $file, bool $shared, int $polling = 100, CancellationToken $token = null): Promise
{
Expand All @@ -377,7 +379,7 @@ function lock(string $file, bool $shared, int $polling = 100, CancellationToken
}
$operation |= LOCK_NB;
$res = \fopen($file, 'c');
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Shouldn't we just open the file here instead of the additional touch above?

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Well technically yes, but then the touching wouldn't be async.

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Well, the fopen isn't async anyway? I guess we'd have to add the function to Handle to have it really async?

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Well, fopen isn't async, but afaik there is no way to obtain a lock using any of the native async libs supported by amphp.
I thought it'd be nice if we could make at least the touch part of the fopen async.

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@trowski What's your opinion here?

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I'm rather uncomfortable introducing anything that can block when it could be rolled into a simple Task executed using parallel.


while (!\flock($res, $operation, $wouldblock)) {
if (!$wouldblock) {
throw new FilesystemException("Failed acquiring lock on file.");
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Should we check for the file being deleted here and recreate it? I guess it could make sense to delete after unlocking, but not in every case (i.e. only if it's a separate lock file).

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I really don't think this is the place for such logic

Expand All @@ -386,13 +388,16 @@ function lock(string $file, bool $shared, int $polling = 100, CancellationToken
$token->throwIfRequested();
}

return static function () use (&$res) {
if ($res) {
\flock($res, LOCK_UN);
\fclose($res);
$res = null;
return new Lock(
0,
static function () use (&$res) {
if ($res) {
\flock($res, LOCK_UN);
\fclose($res);
$res = null;
}
}
};
);
});
}

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17 changes: 9 additions & 8 deletions test/HandleTest.php
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Expand Up @@ -6,6 +6,7 @@
use Amp\Delayed;
use Amp\File;
use Amp\PHPUnit\TestCase;
use Amp\Sync\Lock;
use Amp\TimeoutCancellationToken;

use function Amp\Promise\timeout;
Expand Down Expand Up @@ -268,7 +269,7 @@ public function testExclusiveLock()
try {
try {
$primary = yield $this->tryLockExclusive(__FILE__, 100, 100);
$this->assertInstanceOf(\Closure::class, $primary);
$this->assertInstanceOf(Lock::class, $primary);

$unlocked = false;
$try = $this->tryLockShared(__FILE__, 100, 10000);
Expand All @@ -283,18 +284,18 @@ public function testExclusiveLock()
$this->assertFalse($unlocked, "The lock wasn't acquired");
} finally {
if ($primary) {
$primary();
$primary->release();
}
}

yield new Delayed(100 * 2);
$this->assertTrue($unlocked, "The lock wasn't released");

yield $try;
$this->assertInstanceOf(\Closure::class, $secondary);
$this->assertInstanceOf(Lock::class, $secondary);
} finally {
if ($secondary) {
$secondary();
$secondary->release();
}
}
});
Expand All @@ -306,15 +307,15 @@ public function testSharedLock()
$secondary = null;
try {
$primary = yield $this->tryLockShared(__FILE__, 100, 100);
$this->assertInstanceOf(\Closure::class, $primary);
$this->assertInstanceOf(Lock::class, $primary);
$secondary = yield $this->tryLockShared(__FILE__, 100, 100);
$this->assertInstanceOf(\Closure::class, $secondary);
$this->assertInstanceOf(Lock::class, $secondary);
} finally {
if ($primary) {
$primary();
$primary->release();
}
if ($secondary) {
$secondary();
$secondary->release();
}
}
});
Expand Down