86 lines
4.4 KiB
Markdown
86 lines
4.4 KiB
Markdown
# Asyncdispatch hard fork
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[](https://travis-ci.org/status-im/nim-asyncdispatch2) [](https://ci.appveyor.com/project/cheatfate/nim-asyncdispatch2)
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## Core differences between asyncdispatch and asyncdispatch2
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1. Unified callback type `CallbackFunc`:
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Current version of asyncdispatch uses many types of callbacks:
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* `proc ()` is used in callSoon() callbacks and Future[T] completion callbacks.
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* `proc (fut: Future[T])` is used in Future[T] completion callbacks.
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* `proc (fd: AsyncFD, bytesTransferred: Dword, errcode: OSErrorCode)` is used in Windows IO completion callbacks.
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* `proc (fd: AsyncFD): bool` is used in Unix IO event callbacks.
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Such a large number of different types creates big problems in the storage and processing of callbacks and in interaction between callbacks. Lack of ability to pass custom user data to
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a callback also creates difficulties and inefficiency with passing custom, user-defined data needed for using closures (one more allocation).
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To resolve this issue, we have introduced a unified callback type, `CallbackFunc`:
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```nim
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type
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CallbackFunc* = proc (arg: pointer = nil) {.gcsafe.}
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```
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Also, one more type was introduced for the callback storage, `AsyncCallback`:
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```nim
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type
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AsyncCallback* = object
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function*: CallbackFunc
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udata*: pointer
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```
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2. The order of Future[T] completion callbacks:
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Current version of asyncdispatch processes Future[T] completion callbacks in reverse order, but asyncdispatch2 schedules callbacks in forward order: https://github.com/nim-lang/Nim/issues/7197
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3. Changed the behavior of OS descriptor event callbacks:
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For some unknown reason, the current version of asyncdispatch uses seq[T] to hold a list of descriptor event listeners. However, in the asynchronous environment, there is no need for a list of event listeners. In asyncdispatch2, there is only one place for one READ listener and one place for one WRITE listener.
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4. Removed the default timeout value for the poll() procedure, which allows incorrect usage of asyncdispatch and produces 500-ms timeouts in correct usage.
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5. Changed the behavior of the scheduler in the poll() procedure, and fixed the following issues:
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* https://github.com/nim-lang/Nim/issues/7758
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* https://github.com/nim-lang/Nim/issues/7197
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* https://github.com/nim-lang/Nim/issues/7193
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* https://github.com/nim-lang/Nim/issues/7192
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* https://github.com/nim-lang/Nim/issues/6846
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* https://github.com/nim-lang/Nim/issues/6929
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6. Asyncdispatch2 no longer uses `epochTime()`; instead, it uses the fastest time primitives for a specific OS, `fastEpochTime()`. Also, because MacOS supports only a millisecond resolution in `kqueue`, sub-millisecond resolution is not needed. For details, see https://github.com/nim-lang/Nim/issues/3909.
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7. Removed all IO primitives (`recv()`, `recvFrom()`, `connect()`, `accept()`, `send()`, and `sendTo()`) from the public API, and moved all their functionality into Transports.
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8. Introduced an `addTimer()` / `removeTimer()` callback interface.
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9. Introduced `removeReader()` for `addReader()` and `removeWriter()` for `addWriter()`.
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10. Changed the behavior of the `addReader()`, `addWriter()`, and `addTimer()` callbacks. Now, only the explicit removal of the callbacks must be supplied via `removeReader()`, `removeWriter()`, and `removeTimer()`.
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11. Added the support for the cross-platform `sendfile()` operation.
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12. Removed the expensive `AsyncEvent` and the support for hardware timers and `addProcess`. `addProcess` will be implemented as SubprocessTransport, while hardware-based `AsyncEvent` will be renamed to `ThreadAsyncEvent`.
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13. Added cheap synchronization primitives: `AsyncLock`, `AsyncEvent`, and `AsyncQueue[T]`.
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## Installation
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You can use Nim official package manager `nimble` to install `asyncdispatch2`. The most recent version of the library can be installed via:
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```
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$ nimble install https://github.com/status-im/nim-asyncdispatch2
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```
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## License
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Licensed under one of the following:
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* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
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* MIT license: [LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT
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## TODO
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* Pipe/Subprocess Transports.
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* Multithreading Stream/Datagram servers
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* Future[T] cancelation
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