Fix hdrHeap/hdrStrHeap allocator inuse metric underflow

[moonchen]

Problem

With ENABLE_ALLOCATOR_METRICS=ON, proxy.process.allocator.inuse.hdrHeap
and proxy.process.allocator.inuse.hdrStrHeap go deeply negative —
observed wrapping around as a huge uint64 value (displayed ~ -5.8e10).
Every other allocator's inuse stays sane.

Root cause

hdrHeapAllocator and strHeapAllocator are plain Allocator globals,
and their objects are allocated with no constructor arguments
(THREAD_ALLOC(hdrHeapAllocator, this_ethread()), then a manual
init()/placement-new). With no extra args, THREAD_ALLOC resolves to
the non-templated overload
thread_alloc(Allocator &, ProxyAllocator &) in ProxyAllocator.cc
rather than the templated thread_alloc(CAlloc &, ProxyAllocator &, Args &&...)
in ProxyAllocator.h.

The two overloads diverged:

• The templated overload (used by every ClassAllocator<> allocator —
  IO buffers, sessions, etc.) calls a.increment_for_alloc() when it
  reuses an object from the per-thread freelist.
• The non-templated overload did not.

Meanwhile THREAD_FREE always decrements inuse (UPDATE_FREE_METRICS)
when an object is pushed onto the freelist. So for these two allocators,
every reuse-from-freelist decremented inuse with no matching increment,
and the counter marched negative until it wrapped. Only hdrHeap and
hdrStrHeap hit the non-templated overload, which is why only they
underflowed.

Fix

Add the missing increment_for_alloc() to the freelist-reuse path of the
non-templated thread_alloc, mirroring the templated overload, so the two
paths stay symmetric. Guarded by TS_USE_ALLOCATOR_METRICS.

Test

Added a regression test in test_HdrHeap.cc (guarded by
TS_USE_ALLOCATOR_METRICS) that enables the per-thread freelist and cycles
a single hdrHeap/hdrStrHeap block through free→reuse 1000 times,
asserting inuse returns to baseline+1 and never dips below the starting
value.

Before the fix the test fails as inuse reaches -999/-1000
(reproducing the underflow); after the fix it passes. The full
test_proxy_hdrs suite is green.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes allocator inuse metric underflow for hdrHeap / hdrStrHeap when TS_USE_ALLOCATOR_METRICS is enabled by making the non-templated thread_alloc(Allocator &, ProxyAllocator &) update metrics consistently with the templated overload, and adds a regression unit test to prevent recurrence.

Changes:

• Update the non-templated thread_alloc(Allocator &, ProxyAllocator &) freelist-reuse path to call increment_for_alloc() under TS_USE_ALLOCATOR_METRICS.
• Add a Catch2 regression test that repeatedly frees/reuses a single block via the per-thread freelist and asserts inuse remains balanced for hdrHeap and hdrStrHeap.
• Add metrics-related includes and helpers in the HdrHeap unit test (guarded by TS_USE_ALLOCATOR_METRICS).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/iocore/eventsystem/ProxyAllocator.cc	Fixes allocator metrics accounting symmetry on freelist reuse for the non-templated thread_alloc.
src/proxy/hdrs/unit_tests/test_HdrHeap.cc	Adds a regression test to validate inuse remains stable across freelist free→reuse cycles for hdr heap allocators.

[bryancall]

(duplicate — disregard; see my other approval)

[bryancall]

Approve. Correctly fixes the inuse underflow: the non-templated thread_alloc freelist-reuse path was missing the increment_for_alloc() that THREAD_FREE always pairs with, so frees outran allocs and inuse.{hdrHeap,hdrStrHeap} wrapped. Restores symmetry with the templated overload; regression test (RAII-guarded cmd_disable_pfreelist) is solid. CI green.

Duplicate review double-posted by tooling — dismissing; the identical approval below stands.