The document discusses generators, fibers, and coroutines in PHP. It explains that generators allow for yielding values iteratively without building an array, while fibers provide each their own call stack allowing suspension at any point. Coroutines in Swoole make blocking I/O non-blocking through automatic yielding and resuming. Event loops power asynchronous non-blocking I/O by handling callbacks from I/O streams. Both generators and fibers are building blocks for implementing coroutines to improve PHP application concurrency.

1. From Generator to Fiber
The Road to Coroutine
in PHP
@COSCUP 2022
Albert Chen

2. 02 Blocking and Async I/O in PHP
Outline
01 I/O Models in Linux
03 What is Generator?
04 What is Fiber in PHP 8.1?
05 How to Use Async I/O with Coroutine?
07 Q&A
06 Coroutines in Swoole

3. Read/Write
Read/Write
(O_NONBLOCK)
I/O Multiplexing
(select/poll/epoll)
AIO
I/O Models in Linux
Simplified Matrix of Linux I/O Models
Blocking Non-Blocking
Synchronous
Asynchronous
(https://developer.ibm.com/articles/l-async)

4. I/O Models in Linux
Synchronous Blocking I/O
(https://developer.ibm.com/articles/l-async)

5. I/O Models in Linux
Synchronous Non-Blocking I/O
(https://developer.ibm.com/articles/l-async)

6. I/O Models in Linux
Asynchronous Blocking I/O
(https://developer.ibm.com/articles/l-async)

7. I/O Models in Linux
Asynchronous Non-Blocking I/O
(https://developer.ibm.com/articles/l-async)

8. I/O Models in Linux
Comparison of the I/O Models
(https://rickhw.github.io/2019/02/27/ComputerScience/IO-Models)

9. Blocking I/O in PHP
All I/O functions in PHP are born to be synchronous
Easy for developers to understand
Less-efficient for utilization of CPU usage

10. sleep file_get_contents shell_exec end
Blocking I/O in PHP
1s 3s 3s
process idle
+ +
process idle process idle
7s
=

11. 1s worker
1s worker
1s worker
Blocking I/O in PHP
If one request takes 1s in I/O waiting
Each worker can handle only one request and the same time
Concurrency in PHP depends on worker numbers
Context switch between processes are expensive!
request
request
request

12. Asynchronous I/O in PHP
The simplest but worst-performant solution in PHP
spatie/async package (needs pcntl and posix extensions)

13. Asynchronous I/O in PHP
The simplest but worst-performant solution in PHP
spatie/async package (needs pcntl and posix extensions)
worker
process process
fork
fork

14. Asynchronous I/O in PHP
ReactPHP

15. Asynchronous I/O in PHP
ReactPHP

16. Asynchronous I/O in PHP
Amp

17. Asynchronous I/O in PHP
Amp

18. Asynchronous I/O in PHP
Async I/O Extensions in PHP
ext-event: libevent wrapper
ext-ev: libev wrapper
ext-uv: libuv wrapper
Both ReactPHP and Amp support these extensions as
event-loop drivers

19. select poll epoll
Data
Structue
Array Linked List
Red–Black
Tree
Big O O(n) O(n) O(log(n))
FD Limit
1024 (x86)
2048 (x64)
Unlimited Unlimited
Asynchronous I/O in PHP
I/O Multiplexing in Linux

20. Asynchronous I/O in PHP
I/O Multiplexing in Linux
(http://daemonforums.org/showthread.php?t=2124)

21. Asynchronous I/O in PHP
Event Loop
Event Queue
Stream
Stream
Stream
Stream
Stream
Event Loop
callbacks

22. Asynchronous I/O in PHP
Event Loop in ReactPHP

23. Asynchronous I/O in PHP
Event Loop in ReactPHP

24. Generator
Supported since PHP 5.5
Generator provides an easy way to implement simple iterators
Generator allows you to write code that uses foreach to iterate over
a set of data without needing to build an array in memory
Generator can yield as many times as it needs to provide the values
to be iterated over
(From official PHP manual)

25. Generator
Reading large file with Generator
Regular Version Generator Version
(https://clouding.city/php/generator)

26. Generator
Generators, also known as semi-coroutines, are a subset of
coroutines
Coroutines can control where execution continues immediately
after they yield, while Generators cannot, instead transferring
control back to the generator's caller
The yield statement in a generator does not specify a coroutine
to jump to, but rather passes a value back to a parent routine
A PHP based Coroutine Scheduler needs to implemented for
stackful coroutine
(From Wikipedia)

27. Generators
yield iteration
Generator
two way data transfer
Two Way Data Transfer in Generator

28. Generator
Two Way Data Transfer in Generator
?
(https://www.npopov.com/2012/12/22/Cooperative-multitasking-using-coroutines-in-PHP.html)

29. Generator
Two Way Data Transfer in Generator
yield1
ret1
yield2
ret2
NULL
the first var_dump in gen
the var_dump of the send()
again from within gen
the return value of send()
(https://www.npopov.com/2012/12/22/Cooperative-multitasking-using-coroutines-in-PHP.html)

30. Generator
Generator in ReactPHP's Coroutine
(https://github.com/reactphp/async)

31. Generator
Generator in ReactPHP's Coroutine
(https://github.com/reactphp/async/blob/4.x/src/functions.php)

32. Generator
Generator in ReactPHP's Coroutine
(https://github.com/reactphp/async/blob/4.x/src/functions.php)

33. Generator
Generator in Amp's Coroutine
(https://amphp.org/http-client)

34. Generator
Generator in Amp's Coroutine
(https://github.com/amphp/amp/blob/master/lib/Coroutine.php)

35. Generator
Generator in Amp's Coroutine
(https://github.com/amphp/amp/blob/master/lib/Coroutine.php)

36. Generator
Both ReactPHP and Amp use Promise and Generator for Coroutine
Generators
yield promise
Event Loop
Coroutines
subscribe
send/throw

37. Fiber
New feature in PHP 8.1
Submitted and developed by Amp
Unlike stackless Generators, each Fiber has its own call stack,
allowing them to be paused within deeply nested function calls
Execution may be interrupted anywhere in the call stack using
Fiber::suspend()
Once suspended, execution of the fiber may be resumed with any
value using Fiber::resume()
(From official PHP manual)

38. Fiber
Execution in Fiber
(https://php.watch/versions/8.1/fibers)
Sequential Fiber

39. Fiber
Fiber Class

40. Fiber
Basic Usage
?

41. Fiber
Basic Usage
fiber start
fiber suspend
fiber continue
done
the first echo in fiber
value from fiber suspend
value from fiber resume
end message

42. Fiber
Basic Usage
?

43. Fiber
Basic Usage
start fiber 1
end fiber 1
start fiber 2
end fiber 2
done
block here
block here

44. Fiber
Fibers don't make Blocking code
become Non-Blocking magically!

45. Fiber
Basic Usage
?

46. Fiber
Basic Usage
fiber start
0
1
2
3
.........
fiber never suspends

47. Fiber
Fibers only support Cooperative Scheduling
for I/O-bound tasks

48. Fiber
Fiber in ReactPHP
(https://github.com/reactphp/async#async)

49. Fiber
Fiber in ReactPHP
(https://github.com/reactphp/async/blob/4.x/src/functions.php)

50. Fiber
Fiber in ReactPHP
(https://github.com/reactphp/async/blob/4.x/src/functions.php)

51. Fiber
Fiber in Amp
(https://github.com/amphp/http-client/blob/v5/examples/concurrency/1-concurrent-fetch.php)

52. Fiber
Fiber in Amp
(https://github.com/amphp/amp/blob/v3/src/functions.php)

53. Fiber
Fiber in Amp
(https://github.com/revoltphp/event-loop/blob/main/src/EventLoop/FiberLocal.php)

54. Fiber
Both ReactPHP and amp(v3 beta) support Fiber now
A comprehensive coroutine rather than semi-coroutine
Eliminates yield statement for coroutines
Fiber doesn't turn your code into Non-Blocking magically, traditional
blocking code has to be rewritten with asynchronous I/O
Help not too much for most of developers
Fiber provides only bare minimum required to allow user code to
implement full-stack coroutines in PHP
Fiber doesn't support Preemptive Scheduling yet

55. Coroutine in Swoole
Basic Usage
?

56. Coroutine in Swoole
Basic Usage
start coro 1
start to resume 1 @1
resume coro 1 @1
start to resume 1 @2
resume coro 1 @2
main

57. Coroutine in Swoole
Coroutine for Blocking I/O
?

58. Coroutine in Swoole
Coroutine for Blocking I/O
coroutine start
xxx.xxx.xxx.xxx
coroutine end
main
block here

59. Coroutine in Swoole
Coroutine for Blocking I/O
?

60. Coroutine in Swoole
Coroutine for Blocking I/O
coroutine start
main
xxx.xxx.xxx.xxx
coroutine end
auto yield
auto resume

61. Coroutine in Swoole
Preemptive Scheduling
?

62. Coroutine in Swoole
Preemptive Scheduling
infinite loop

63. Coroutine in Swoole
Preemptive Scheduling
?

64. Coroutine in Swoole
Fatal error: Uncaught Exception:
12.5ms end in xxx
Stack trace:
#0 {main}
thrown in xxx
Preemptive Scheduling

65. Coroutine in Swoole
Channel
?

66. Coroutine in Swoole
Channel
[coroutine 3]
int(0)
[coroutine 2] - 0
[coroutine 3]
int(1)
[coroutine 2] - 1
[coroutine 3]
......
second coroutine
second coroutine
second coroutine
popped value
popped value
first coroutine
first coroutine

67. Coroutine in Swoole
Swoole implements its full coroutine features
Built-in Blocking I/O functions can be replaced to Non-Blocking I/O
automatically if hook flags are set
Swoole supports Preemptive Scheduling for CPU-bound tasks
Swoole Provides CSP Model for Coroutine Communications like in
GoLang
Yields and resumes take place behind the scenes for I/O functions
switching

68. Questions
What's the difference between Asynchronous and Coroutine?
What's the difference between Generator and Fiber?
How to turn Blocking I/O stream turning into Non-Blocking?
What is Event Loop? Is it required for Asynchronous?
What's the benefits of Coroutine?
Is Asynchronous a must for Coroutine?
How to make built-in Blocking I/O functions Asynchronous?
Can Asynchronous I/O be integrated with traditional Blocking I/O
environment? (e.g. PHP-FPM)

69. Q&A