siddharthmittal13 opened a new pull request, #590:
URL: https://github.com/apache/avro-rs/pull/590
## What
Closes #589.
Adds an **opt-in** cargo feature `custom_allocator` (off by default) that
exposes a new `apache_avro::alloc` module with two custom `GlobalAlloc`
implementations:
1. **`CustomAllocator`** — a minimal allocator that delegates every
operation to the `System` allocator. A ready-made base users can install
directly as `#[global_allocator]` or extend to add their own behavior (logging,
pooling, ...) without reimplementing platform allocation logic.
2. **`CountingAllocator<A = System>`** — wraps any inner allocator (defaults
to `System`) and tracks:
- live bytes — `allocated()`
- high-water mark — `peak_allocated()`
- cumulative bytes — `total_allocated()`
- allocation / deallocation counts
- `reset_peak()` for scoped measurement
`const fn` constructors (`CountingAllocator::system()`,
`CountingAllocator::new(inner)`) let it back a `#[global_allocator]` static.
## Why
`apache-avro` currently offers no first-class hook for customizing or
observing heap allocation. The existing `util::max_allocation_bytes` guard only
rejects a *single* oversized length prefix at decode time — it gives no
visibility into the actual live/peak memory a workload uses, and no reusable
building block for custom allocation behavior.
`CountingAllocator` complements `max_allocation_bytes` by measuring real
process memory, including pressure that builds up across many
individually-small allocations.
## Notes
- **Fully opt-in / zero cost when disabled.** The module is gated behind the
`custom_allocator` feature and is inert unless the user installs one of the
types as their `#[global_allocator]`. The default build is unchanged.
- Counters use relaxed atomics (observability, not hard real-time
accounting).
## Testing
- New unit tests for `CustomAllocator` (delegation) and `CountingAllocator`
(alloc/dealloc, peak high-water mark, `reset_peak`, realloc growth/shrink) —
all passing.
- Both module doc examples compile (`--doc`).
- `cargo fmt` and `cargo clippy --features custom_allocator --lib` are clean.
- Default (feature-off) build verified.
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