A global allocator for Wasm that traces allocations and deallocations for debugging purposes.
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Built with ๐ฆ๐ธ by The Rust and WebAssembly Working Group
wasm-tracing-allocator
enables you to better debug and analyze memory leaks
and invalid frees in an environment where we don't have access to the
conventional tools like Valgrind. The tracing hooks are safely implemented in
JS, outside the Wasm module and its linear memory, to ensure that the tracing
code doesn't perturb results.
First, add wasm-tracing-allocator
to your Cargo.toml
's dependency list:
[dependencies]
wasm-tracing-allocator = "0.1.0"
Next, configure wasm_tracing_allocator::WasmTracingAllocator
as the global
allocator:
// src/lib.rs
use std::alloc::System;
use wasm_tracing_allocator::WasmTracingAllocator;
#[global_allocator]
static GLOBAL_ALLOCATOR: WasmTracingAllocator<System> = WasmTracingAllocator(System);
Finally, make the JS implementations of the tracing hooks are available for your Wasm module to import:
-
On the Web, add this script before your Wasm module is instantiated:
<script src="https://unpkg.com/[email protected]/js/hooks.js"></script>
-
On Node.js, require the hooks before your Wasm module is instantiated:
require("wasm-tracing-allocator");
Use your developer tools console to invoke methods of the global
WasmTracingAllocator
object to get analyses about allocations and
deallocations.
The output is typically rendered with console.table
:
Dump a table of live allocations to the console.
WasmTracingAllocator.dumpLiveAllocations({
keyLabel: String,
valueLabel: String,
getKey: Object => any,
getValue: Object => Number,
});
-
keyLabel
: Optional. The string label used to describe the keys column in the table. -
valueLabel
: Optional. The string label used to describe the values column in the table. -
getKey
: Optional. Function from an allocation entry object to anything. The table will group and aggregate entries by their keys. Defaults to the stack at the time of the allocation. -
getValue
: Optional. Function from an allocation entry object to a number. The values for all entries with the same key are summed. Defaults to the byte size of each allocation; a potential alternative would be to ignore the argument and return1
to count the number of allocations instead.
Dump a table of invalid frees (double frees, frees of things that were never allocated, etc...) to the console.
WasmTracingAllocator.dumpInvalidFrees({
keyLabel: String,
valueLabel: String,
getKey: Object => any,
getValue: Object => Number,
});
-
keyLabel
: Optional. The string label used to describe the keys column in the table. -
valueLabel
: Optional. The string label used to describe the values column in the table. -
getKey
: Optional. Function from an invalid free entry object to anything. The table will group and aggregate entries by their keys. Defaults to the stack at the time of the deallocation. -
getValue
: Optional. Function from an invalid free entry object to a number. The values for all entries with the same key are summed. Defaults to counting the number of invalid frees.