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