Stream: git-wasmtime

Topic: wasmtime / PR #3925 Delete historical interruptable suppo...

Wasmtime GitHub notifications bot (Mar 14 2022 at 15:40):

alexcrichton opened PR #3925 from delete-interurpts to main:

This commit removes the Config::interruptable configuration along with
the InterruptHandle type from the wasmtime crate. The original
support for adding interruption to WebAssembly was added pretty early on
in the history of Wasmtime when there was no other method to prevent an
infinite loop from the host. Nowadays, however, there are alternative
methods for interruption such as fuel or epoch-based interruption.

One of the major downsides of Config::interruptable is that even when
it's not enabled it forces an atomic swap to happen when entering
WebAssembly code. This technically could be a non-atomic swap if the
configuration option isn't enabled but that produces even more branch-y
code on entry into WebAssembly which is already something we try to
optimize. Calling into WebAssembly is on the order of a dozens of
nanoseconds at this time and an atomic swap, even uncontended, can add
up to 5ns on some platforms.

The main goal of this PR is to remove this atomic swap on entry into
WebAssembly. This is done by removing the Config::interruptable field
entirely, moving all existing consumers to epochs instead which are
suitable for the same purposes. This means that the stack overflow check
is no longer entangled with the interruption check and perhaps one day
we could continue to optimize that further as well.

Some consequences of this change are:

• Epochs are now the only method of remote-thread interruption.

• There are no more Wasmtime traps that produces the Interrupted trap
  code, although we may wish to move future traps to this so I left it
  in place.

• The C API support for interrupt handles was also removed and bindings
  for epoch methods were added.

• Function-entry checks for interruption are a tiny bit less efficient
  since one check is performed for the stack limit and a second is
  performed for the epoch as opposed to the Config::interruptable
  style of bundling the stack limit and the interrupt check in one. It's
  expected though that this is likely to not really be measurable.

• The old VMInterrupts structure is renamed to VMRuntimeLimits.

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Wasmtime GitHub notifications bot (Mar 14 2022 at 15:40):

alexcrichton updated PR #3925 from delete-interurpts to main.

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:02):

alexcrichton updated PR #3925 from delete-interurpts to main.

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:10):

cfallin submitted PR review.

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:10):

cfallin created PR review comment:

Should we note here that it's also signal-safe (I think we have a similar note in the rustdoc text)?

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:10):

cfallin created PR review comment:

Update type here in the doc comment (VMRuntimeLimits)?

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:10):

cfallin submitted PR review.

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:10):

cfallin created PR review comment:

    /// WebAssembly code by instrumenting generated code to consume fuel as it

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:10):

cfallin created PR review comment:

    /// This can be used to deterministically prevent infinitely-executing

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:21):

alexcrichton updated PR #3925 from delete-interurpts to main.

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:39):

sunfishcode submitted PR review.

Wasmtime GitHub notifications bot (Mar 14 2022 at 16:39):

sunfishcode created PR review comment:

 * \brief Configures WASI state within the specified store.

Wasmtime GitHub notifications bot (Mar 14 2022 at 18:24):

alexcrichton updated PR #3925 from delete-interurpts to main.

Wasmtime GitHub notifications bot (Mar 14 2022 at 20:25):

alexcrichton merged PR #3925.

Last updated: Oct 23 2024 at 20:03 UTC