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# Concurrency Component for Icicle
**Under development.**
**Under development -- keep an eye out for things to come in the near future though!**
Concurrent provides a means of parallelizing code without littering your application with complicated lock checking and inter-process communication.
To be as flexible as possible, Concurrent comes with a collection of non-blocking concurrency tools that can be used independently as needed, as well as an "opinionated" task API that allows you to assign units of work to a pool of worker threads or processes.
#### Requirements
- PHP 5.5+
- [pthreads](http://pthreads.org) for multithreading *or*
- System V-compatible UNIX OS and PHP with `--enable-pcntl` and `--enable-sysvsem`
- System V-compatible Unix OS and PHP with `--enable-pcntl`
#### Benchmarks
A few benchmarks are provided for analysis and study. Can be used to back up implementation decisions, or to measure performance on different platforms or hardware.
@ -14,19 +16,64 @@ A few benchmarks are provided for analysis and study. Can be used to back up imp
vendor/bin/athletic -p benchmarks -b vendor/autoload.php
## Documentation
Concurrent can use either process forking or true threading to parallelize execution. Threading provides better performance and is compatible with UNIX and Windows but requires ZTS (Zend thread-safe) PHP, while forking has no external dependencies but is only compatible with UNIX systems. If your environment works meets neither of these requirements, this library won't work.
Concurrent can use either process forking or true threading to parallelize execution. Threading provides better performance and is compatible with Unix and Windows but requires ZTS (Zend thread-safe) PHP, while forking has no external dependencies but is only compatible with Unix systems. If your environment works meets neither of these requirements, this library won't work.
### Contexts
Concurrent provides a generic interface for working with parallel tasks called "contexts". All contexts are capable of being executed in parallel from the main program code. Each context is able to safely share data stored in member variables of the context object.
Concurrent provides a generic interface for working with parallel tasks called "contexts". All contexts are capable of being executed in parallel from the main program code. Each context is assigned a closure to execute when it is created, and the returned value is passed back to the parent context. Concurrent goes for a "shared-nothing" architecture, so any variables inside the closure are local to that context and can store any non-safe data.
#### Synchronization
Contexts wouldn't be very useful if they couldn't work on a shared data set. Contexts allow you to share any serializable objects via the properties of a context.
You can wait for a context to close by calling `join()`. Joining does not block the parent context and will asynchronously wait for the child context to finish before resolving.
```php
use Icicle\Concurrent\Threading\ThreadContext;
use Icicle\Coroutine;
use Icicle\Loop;
Coroutine\create(function () {
$thread = new ThreadContext(function () {
print "Hello, World!\n";
});
$thread->start();
yield $thread->join();
});
Loop\run();
```
#### Synchronization with channels
Contexts wouldn't be very useful if they couldn't be given any data to work on. The recommended way to share data between contexts is with a `Channel`. A channel is a low-level abstraction over local, non-blocking sockets, which can be used to pass messages and objects between two contexts. Channels are non-blocking and do not require locking. For example:
```php
use Icicle\Concurrent\Sync\Channel;
use Icicle\Concurrent\Threading\ThreadContext;
use Icicle\Coroutine;
use Icicle\Loop;
Coroutine\create(function () {
list($socketA, $socketB) = Channel::createSocketPair();
$channel = new Channel($socketA);
$thread = new ThreadContext(function ($socketB) {
$channel = new Channel($socketB);
yield $channel->send("Hello!");
}, $socketB);
$thread->start();
$message = (yield $channel->receive());
yield $thread->join();
});
Loop\run();
```
### Synchronization with parcels
Parcels are shared containers that allow you to store context-safe data inside a shared location so that it can be accessed by multiple contexts. To prevent race conditions, you still need to access a parcel's data exclusively, but Concurrent allows you to acquire a lock on a parcel asynchronously without blocking the context execution, unlike traditional mutexes.
### Threading
Threading is a cross-platform concurrency method that is fast and memory efficient. Thread contexts take advantage of an operating system's multi-threading capabilities to run code in parallel.
### Forking
For UNIX-like systems, you can create parallel execution using fork contexts. Though not as efficient as multi-threading, in some cases forking can take better advantage of some multi-core processors than threads. Fork contexts use the `pcntl_fork()` function to create a copy of the current process and run alternate code inside the new process.
For Unix-like systems, you can create parallel execution using fork contexts. Though not as efficient as multi-threading, in some cases forking can take better advantage of some multi-core processors than threads. Fork contexts use the `pcntl_fork()` function to create a copy of the current process and run alternate code inside the new process.
## License
All documentation and source code is licensed under the Apache License, Version 2.0 (Apache-2.0). See the [LICENSE](LICENSE) file for details.