45 lines
1.9 KiB
Markdown
45 lines
1.9 KiB
Markdown
Maximum Number of Operations
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===========================
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{{#include ../links.md}}
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Limit How Long a Script Can Run
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------------------------------
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Rhai by default does not limit how much time or CPU a script consumes.
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This can be changed via the `Engine::set_max_operations` method, with zero being unlimited (the default).
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The _operations count_ is intended to be a very course-grained measurement of the amount of CPU that a script
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has consumed, allowing the system to impose a hard upper limit on computing resources.
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A script exceeding the maximum operations count terminates with an error result.
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This can be disabled via the [`unchecked`] feature for higher performance (but higher risks as well).
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```rust
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let mut engine = Engine::new();
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engine.set_max_operations(500); // allow only up to 500 operations for this script
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engine.set_max_operations(0); // allow unlimited operations
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```
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What Does One _Operation_ Mean
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-----------------------------
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The concept of one single _operation_ in Rhai is volatile – it roughly equals one expression node,
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loading one variable/constant, one operator call, one iteration of a loop, or one function call etc.
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with sub-expressions, statements and function calls executed inside these contexts accumulated on top.
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A good rule-of-thumb is that one simple non-trivial expression consumes on average 5-10 operations.
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One _operation_ can take an unspecified amount of time and real CPU cycles, depending on the particulars.
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For example, loading a constant consumes very few CPU cycles, while calling an external Rust function,
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though also counted as only one operation, may consume much more computing resources.
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To help visualize, think of an _operation_ as roughly equals to one _instruction_ of a hypothetical CPU
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which includes _specialized_ instructions, such as _function call_, _load module_ etc., each taking up
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one CPU cycle to execute.
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