Trait wasmi::ResourceLimiter

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pub trait ResourceLimiter {
    // Required methods
    fn memory_growing(
        &mut self,
        current: usize,
        desired: usize,
        maximum: Option<usize>
    ) -> Result<bool, MemoryError>;
    fn table_growing(
        &mut self,
        current: u32,
        desired: u32,
        maximum: Option<u32>
    ) -> Result<bool, TableError>;

    // Provided methods
    fn memory_grow_failed(&mut self, _error: &MemoryError) { ... }
    fn table_grow_failed(&mut self, _error: &TableError) { ... }
    fn instances(&self) -> usize { ... }
    fn tables(&self) -> usize { ... }
    fn memories(&self) -> usize { ... }
}

Expand description

Used by hosts to limit resource consumption of instances.

This trait is used in conjunction with the Store::limiter to limit the allocation of resources within a store. As a store-level limit this means that all creation of instances, memories, and tables are limited within the store. Resources limited via this trait are primarily related to memory and limiting CPU resources needs to be done with something such as Config::consume_fuel.

Note that this trait does not limit 100% of memory allocated via a Store. Wasmi will still allocate memory to track data structures and additionally embedder-specific memory allocations are not tracked via this trait. This trait only limits resources allocated by a WebAssembly instance itself.

Required Methods§

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fn memory_growing( &mut self, current: usize, desired: usize, maximum: Option<usize> ) -> Result<bool, MemoryError>

Notifies the resource limiter that an instance’s linear memory has been requested to grow.

current is the current size of the linear memory in bytes.
desired is the desired size of the linear memory in bytes.
maximum is either the linear memory’s maximum or a maximum from an instance allocator, also in bytes. A value of None indicates that the linear memory is unbounded.

The current and desired amounts are guaranteed to always be multiples of the WebAssembly page size, 64KiB.

§Return Value

If Ok(true) is returned from this function then the growth operation is allowed. This means that the wasm memory.grow instruction will return with the desired size, in wasm pages. Note that even if Ok(true) is returned, though, if desired exceeds maximum then the growth operation will still fail.

If Ok(false) is returned then this will cause the memory.grow instruction in a module to return -1 (failure), or in the case of an embedder API calling Memory::new or Memory::grow an error will be returned from those methods.

§Errors

If Err(e) is returned then the memory.grow function will behave as if a trap has been raised. Note that this is not necessarily compliant with the WebAssembly specification but it can be a handy and useful tool to get a precise backtrace at “what requested so much memory to cause a growth failure?”.

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fn table_growing( &mut self, current: u32, desired: u32, maximum: Option<u32> ) -> Result<bool, TableError>

Notifies the resource limiter that an instance’s table has been requested to grow.

current is the current number of elements in the table.
desired is the desired number of elements in the table.
maximum is either the table’s maximum or a maximum from an instance allocator. A value of None indicates that the table is unbounded.