61 lines
2.3 KiB
Markdown
61 lines
2.3 KiB
Markdown
Performance Build
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=================
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{{#include ../../links.md}}
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Some features are for performance. For example, using [`only_i32`] or [`only_i64`] disables all other integer types (such as `u16`).
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Use Only One Integer Type
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------------------------
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If only a single integer type is needed in scripts - most of the time this is the case - it is best to avoid registering
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lots of functions related to other integer types that will never be used. As a result, [`Engine`] creation will be faster
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because fewer functions need to be loaded.
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The [`only_i32`] and [`only_i64`] features disable all integer types except `i32` or `i64` respectively.
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Use Only 32-Bit Numbers
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----------------------
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If only 32-bit integers are needed - again, most of the time this is the case - turn on [`only_i32`].
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Under this feature, only `i32` is supported as a built-in integer type and no others.
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On 64-bit targets this may not gain much, but on certain 32-bit targets this improves performance
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due to 64-bit arithmetic requiring more CPU cycles to complete.
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Minimize Size of `Dynamic`
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-------------------------
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Turning on [`no_float`] and [`only_i32`] on 32-bit targets makes the critical [`Dynamic`] data type only 8 bytes long.
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Normally [`Dynamic`] can be up to 16 bytes (e.g. on x86/x64 CPU's) in order to hold an `i64` or `f64`.
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A small [`Dynamic`] helps performance due to better cache efficiency.
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Use `ImmutableString`
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--------------------
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Internally, Rhai uses _immutable_ [strings] instead of the Rust `String` type. This is mainly to avoid excessive
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cloning when passing function arguments.
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Rhai's internal string type is `ImmutableString` (basically `Rc<String>` or `Arc<String>` depending on the [`sync`] feature).
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It is cheap to clone, but expensive to modify (a new copy of the string must be made in order to change it).
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Therefore, functions taking `String` parameters should use `ImmutableString` or `&str` (both map to `ImmutableString`)
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for the best performance with Rhai.
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Disable Closures
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----------------
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Support for [closures] that capture shared variables adds material overhead to script evaluation.
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This is because every data access must be checked whether it is a shared value and, if so, take a read
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lock before reading it.
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Use [`no_closure`] to disable closure and capturing support to optimize the hot path
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because there is no need to take locks for shared data.
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