low_wasm_memory

Low Wasm memory hook

This example demonstrates the low Wasm memory hook on the Internet Computer. The ICP runtime automatically executes a special on_low_wasm_memory system function when a canister's available Wasm memory falls below the configured wasm_memory_threshold. The example shows the execution order of the heartbeat and on_low_wasm_memory system functions as the canister progressively allocates memory until the threshold is reached.

For more information, see the low Wasm memory hook specification.

Build and deploy from the command line

Prerequisites

• Node.js
• icp-cli: npm install -g @icp-sdk/icp-cli @icp-sdk/ic-wasm

Install

git clone https://github.com/dfinity/examples
cd examples/rust/low_wasm_memory

Deploy and test

icp network start -d
icp deploy
bash test.sh
icp network stop

icp.yaml sets wasm_memory_limit to 8 MiB and wasm_memory_threshold to 2 MiB. The on_low_wasm_memory hook fires when usage exceeds 8 − 2 = 6 MiB.

bash test.sh polls get_executed_functions_order until OnLowWasmMemory appears as the last entry (or times out after 60 s).

To observe the execution order manually:

icp canister call --query backend get_executed_functions_order '()'

Repeat until the last entry is OnLowWasmMemory.

Security considerations and best practices

Refer to the security best practices for information on security and best practices for your ICP app.