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1.8 KiB
47 lines
1.8 KiB
# Reference counting
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[Netty][netty] uses reference counting for some objects, such as `ByteBuf`s. The
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Netty documentation explains its
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[use of reference counting][netty-ref-counting] in more detail.
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OpenRS2 has an extension method that automatically wraps a block of code in a
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`try`/`finally` block, calling `release()` in the `finally` block. It is very
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similar to Kotlin's extension method for `close()`ing `Closeable`s (and in fact
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has the same name: `use`).
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A typical pattern for allocating and then releasing a `ByteBuf` using this
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method is:
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```kt
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alloc.buffer().use { buf ->
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// use buf here
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}
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```
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In OpenRS2, a method that consumes a `ByteBuf` is generally not responsible for
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releasing it - the caller is. This provides more flexibility, as the caller
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might want to continue reading from the buffer. (For example, after calling
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`Js5Compression.uncompress()`, the caller will probably want to read the 2 byte
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version trailer from the same buffer.)
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For obvious reasons, a method that produces a `ByteBuf` is generally not
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responsible for releasing it - again, the caller is. However, arranging for the
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`ByteBuf` to be freed if an exception occurs between the `ByteBuf` being
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allocated and returned is tricky. The following pattern is useful for correctly
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releasing/retaining the buffer depending on whether an exception occurs or not:
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```kt
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alloc.buffer().use { buf ->
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// write to buf here
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return buf.retain()
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}
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```
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If any of the code prior to the `return` fails, the buffer is released.
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If the `return` is reached, no more exceptions can occur. The reference count is
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increased to counteract the `finally` block decreasing it, such that by the time
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the buffer reaches the caller its reference count is 1.
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[netty]: https://netty.io/
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[netty-ref-counting]: https://netty.io/wiki/reference-counted-objects.html
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