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Temporarily immortalize objects that use deferred reference counting #117783

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colesbury opened this issue Apr 11, 2024 · 2 comments
Closed

Temporarily immortalize objects that use deferred reference counting #117783

colesbury opened this issue Apr 11, 2024 · 2 comments
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topic-free-threading type-feature A feature request or enhancement

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@colesbury
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colesbury commented Apr 11, 2024 •
edited by bedevere-app bot
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Feature or enhancement

Work is ongoing to implement deferred reference counting in the free-threaded build. The goal is to avoid many of the scaling bottlenecks caused by reference count contention. However, the work is complex and may not be finished in time for the 3.13 beta release and feature freeze.

In the meantime, we should temporarily immortalize objects that would use deferred reference counting in order to avoid bottlenecks that would inhibit scaling.

This has some real downsides: objects that are immortalized are never collected so an application that repeatedly creates many of these objects will leak memory. I think the trade-off is still worth it: if we can't scale multithreaded programs, then the free-threaded build is not particularly useful.

Once we implement deferred reference counting, we will get rid of this.

What types of objects use deferred reference counting?

  • Top-level functions
  • Descriptors
  • Modules and their dictionaries
  • Heap types
  • Code objects

Refleak buildbots

We want the free-threading refleak buildbots to continue to work and catch leaks. In order to do that, we'll want to:

  1. Only do the deferred -> immortal conversion when the first non-main thread is started
  2. Disable the conversion at runtime in the refleak tests via an internal API

Linked PRs
@colesbury colesbury added type-feature A feature request or enhancement topic-free-threading labels Apr 11, 2024
colesbury added a commit to colesbury/cpython that referenced this issue Apr 12, 2024
@colesbury
Merge branch 'pythongh-117783-immortalize' into nogil-integration
0351844
colesbury added a commit to colesbury/cpython that referenced this issue Apr 19, 2024
@colesbury
pythongh-117783: Immortalize objects that use deferred reference coun…
9ff8d52 
…ting

Deferred reference counting is not fully implemented yet. As a temporary
measure, we immortalize objects that would use deferred reference
counting to avoid multi-threaded scaling bottlenecks.

This is only performed in the free-threaded build once the first
non-main thread is started. Additionally, some tests, including refleak
tests, suppress this behavior.
colesbury added a commit to colesbury/cpython that referenced this issue Apr 19, 2024
@colesbury
pythongh-117783: Immortalize objects that use deferred reference coun…
30a4133 
…ting

Deferred reference counting is not fully implemented yet. As a temporary
measure, we immortalize objects that would use deferred reference
counting to avoid multi-threaded scaling bottlenecks.

This is only performed in the free-threaded build once the first
non-main thread is started. Additionally, some tests, including refleak
tests, suppress this behavior.
@bedevere-app bedevere-app bot mentioned this issue Apr 19, 2024
Merged
colesbury added a commit to colesbury/cpython that referenced this issue Apr 19, 2024
@colesbury
Merge branch 'pythongh-117783-immortalize' into nogil-integration
539595a
colesbury added a commit that referenced this issue Apr 29, 2024
@colesbury
gh-117783: Immortalize objects that use deferred reference counting (#…
7ccacb2 
…118112)

Deferred reference counting is not fully implemented yet. As a temporary
measure, we immortalize objects that would use deferred reference
counting to avoid multi-threaded scaling bottlenecks.

This is only performed in the free-threaded build once the first
non-main thread is started. Additionally, some tests, including refleak
tests, suppress this behavior.
@morkev morkev mentioned this issue Apr 29, 2024
Closed
@ngoldbaum ngoldbaum mentioned this issue May 3, 2024
Closed
@colesbury
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This is implemented now

This was referenced May 7, 2024
Open
Closed
colesbury added a commit to colesbury/cpython that referenced this issue Jun 1, 2024
@colesbury
pythongh-117657: Fix race involving immortalizing objects
45afd9d 
The free-threaded build currently immortalizes objects that use deferred
reference counting (see pythongh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.
@colesbury colesbury mentioned this issue Jun 1, 2024
Merged
colesbury added a commit that referenced this issue Jun 3, 2024
@colesbury
gh-117657: Fix race involving immortalizing objects (#119927)
47fb432 
The free-threaded build currently immortalizes objects that use deferred
reference counting (see gh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.
colesbury added a commit to colesbury/cpython that referenced this issue Jun 3, 2024
@colesbury
pythongh-117657: Fix race involving immortalizing objects (python#119927
f4e012c 
)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see pythongh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.

(cherry picked from commit 47fb432)
@colesbury colesbury mentioned this issue Jun 3, 2024
Merged
colesbury added a commit that referenced this issue Jun 3, 2024
@colesbury
[3.13] gh-117657: Fix race involving immortalizing objects (GH-119927) (
ae70531 
#120005)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see gh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.

(cherry picked from commit 47fb432)
mliezun pushed a commit to mliezun/cpython that referenced this issue Jun 3, 2024
@colesbury @mliezun
pythongh-117657: Fix race involving immortalizing objects (python#119927
cb8a398 
)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see pythongh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.
barneygale pushed a commit to barneygale/cpython that referenced this issue Jun 5, 2024
@colesbury @barneygale
pythongh-117657: Fix race involving immortalizing objects (python#119927
cc875fa 
)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see pythongh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.
@Fidget-Spinner Fidget-Spinner mentioned this issue Jul 3, 2024
Closed
noahbkim pushed a commit to hudson-trading/cpython that referenced this issue Jul 11, 2024
@colesbury @noahbkim
pythongh-117657: Fix race involving immortalizing objects (python#119927
65cc5e0 
)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see pythongh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.
estyxx pushed a commit to estyxx/cpython that referenced this issue Jul 17, 2024
@colesbury @estyxx
pythongh-117657: Fix race involving immortalizing objects (python#119927
470988f 
)

The free-threaded build currently immortalizes objects that use deferred
reference counting (see pythongh-117783). This typically happens once the
first non-main thread is created, but the behavior can be suppressed for
tests, in subinterpreters, or during a compile() call.

This fixes a race condition involving the tracking of whether the
behavior is suppressed.
@colesbury colesbury mentioned this issue Sep 19, 2024
Closed
@terryjreedy
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Immortalization has been removed in 3.14 #124239 (comment)

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