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Chrome-External Builds

Work is ongoing to make PartitionAlloc a standalone library. The standalone repository for PartitionAlloc is hosted here.

GN Args

External clients should examine the args described in build_overrides/partition_alloc.gni and add them in their own source tree. PartitionAlloc's build will expect them at //build_overrides/partition_alloc.gni.

In addition, something must provide build_with_chromium = false to the PA build system.

use_partition_alloc

The use_partition_alloc GN arg, described in build_config.md, provides a GN-level seam that embedders

  1. can set in their GN args and
  2. should observe in their GN recipes to conditionally pull in PartitionAlloc.

I.E. if you have any reason to disable PartitionAlloc, you should do so with this GN arg. Avoid pulling in PartitionAlloc headers when the corresponding buildflag is false.

Setting use_partition_alloc false will also implicitly disable other features, e.g. nixing the compilation of BackupRefPtr as the implementation of raw_ptr<T>.

Periodic Memory Reduction Routines

PartitionAlloc provides APIs to

Both of these must be called by the embedder external to PartitionAlloc. PA provides neither an event loop nor timers of its own, delegating this to its clients.

Build Considerations

External clients create constraints on PartitionAlloc's implementation.

C++17

PartitionAlloc targets C++17. This is aligned with our first external client, PDFium, and may be further constrained by other clients. These impositions prevent us from moving in lockstep with Chrome's target C++ version.

We do not even have guarantees of backported future features, e.g. C++20's designated initializers. Therefore, these cannot ship with PartitionAlloc.

MSVC Support

PDFium supports MSVC. PartitionAlloc will have to match it.

MSVC Constraint: No Inline Assembly

MSVC's syntax for asm blocks differs from the one widely adopted in parts of Chrome. But more generally, MSVC doesn't support inline assembly on ARM and x64 processors. Assembly blocks should be gated behind compiler-specific flags and replaced with intrinsics in the presence of COMPILER_MSVC (absent __clang__).