This is the initial implementation of hot reload with multi-isolate
groups.
Implementation:
As before, when a service API call triggers a reload it will be routed
as an OOB message to a specific isolate (**). As opposed to before, that
isolate has now to coordinate with all other isolates, ensuring that it
"owns" the reload and all other isolates are waiting in a state that
allows reload.
This is implemented as a [ReloadOperationScope] which first participates
in other reloads (if there are any) and then owns the reload. It will
send a new kind of service message to all other registered isolates. All
of them have to check in before reload can proceed. If a new isolate
is about to join the group, it will participate when registering the
isolate. If an old isolate wants to die, it will participate when
unregistering the isolate.
This means that in addition to the existing StackOverFlow checks that
can process OOB messages and therefore reload, we'll have isolate
registration and unregistration as well as a new
Isolate::kCheckForReload OOB message handler where an isolate can
participate in a reload.
We consider the isolate group to be reloadable if the main isolate has
loaded the program and set the root library. Helper isolates don't need
to load any more kernel code and only initialize core libraries, so it's
fine to reload them during this time.
(**) The reason we continue to send reload service API calls to any
isolate in an isolate group is that re-loading might involve calling out
to the embedder's tag handler. Doing so currently requires an active
isolate.
If we allowed a subset of dart_api.h (the subset needed by the tag
handler) to be used only with an active IsolateGroup instead of an
active Isolate we could remove this requirement.
Edge cases:
There's various edge cases to consider: The main edge case is, we currently
maintain an upper limit to the number of isolates executing in parallel
(to ensure each can have big enough chunk of new space, i.e. TLAB).
If there are more isolates with active work they are waiting until one
of the exiting ones "yields". To ensure progress, if any such actively
running isolate gets a request to participate in a reload, it will mark
its own thread as "blocked" and therefore "yields", so another isolate
can make progress until all isolates are participating and the reload
can start.
Marking an isolate as "blocked" happens by exiting that isolate. It will
free up it's TLAB, decrease active mutator count and (if running on VM's
thread pool) also temporarily increase the thread pool size.
The side-effect of this is that it will use one pthread per isolate
during reload. In the future we can extend this first implementation, by
specially handling isolates that don't have a message handler running.
Doing so would require careful consideration to avoid races.
Testing:
In order to test this we use a small helper framework for reload tests.
The helper framework will, similar to real world reload e.g. in flutter,
will spawn a subprocess. It will use the service API to trigger reloads
in this subproces.
To synchronize between the reload driver and the application being
reloaded it allows watching for events to be printed to stdout/stderr.
The reload test itself can be written - similar to multitests - with
annotations such as `// @include-in-relload-0` in them. The testing
framework will then generate multiple application versions that all get
compiled to kernel.
For simplicity we generate the kernel using the standalone VM with
`--snapshot-kind=kernel` and avoid using the incremental compiler.
There are 4 different tests exercising different aspects of
multi-isolate reload:
vm/dart_2/isolates/reload_active_stack_test:
Performs a reload while a fixed number of isolates have an active
stack, thereby ensuring e.g. that all frames of all isolate mutator
stacks get deoptimized, ...
vm/dart_2/isolates/reload_no_active_stack_test:
Similar to the test above, but instead of having an active stack the
isolates can yield to the event loop, possibly be even descheduled
vm/dart_2/isolates/reload_many_isolates_test:
Similar to the test above, but this test uses many more isolates.
vm/dart_2/isolates/reload_many_isolates_live_and_die_test:
Performs a reload where isolates get spawned and die all the time.
There are always P isolates alive at any given point in time, each
of them spawns children when their parent has died.
Performing a reload catches isolates as various stages of their
lifecycle and can therefore cover a lot of corner cases.
TEST=vm/dart_2/isolates/reload_*_test.dart
Issue https://github.com/dart-lang/sdk/issues/36097
Change-Id: I97039b4084de040b7f2e22f5832a40d57ba398d5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/187461
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>
This removes our temporary scaffolding support for JIT isolate groups
(which was implemented by creating a new isolate group, loading the
application kernel into it and then merging the heap into the original
isolate group - maintaining a different object store)
It makes all isolates within a group share the same object store, same
libraries and JITed code. It will be conservative to start with, only
allow running unoptimized code, etc.
We will gradually remove the restrictions imposed by this CL:
https://dart-review.googlesource.com/c/sdk/+/173970
Issue https://github.com/dart-lang/sdk/issues/36097
TEST=Tests using --enable-isolate-groups with JIT sharing.
Change-Id: I2bf69a6fe3c905067c4cec2e81613f731c52e5ee
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175302
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>
As part of making lightweight isolates work in JIT, we will need to
ensure that whenever a new isolate is spawned it will get it's initial
global field table populated.
In order to achieve this we make the isolate groups initial field table
the authoritive place where we
a) register initial static field values
b) serializer reads them from, deserializer writes them to
This allows us to also remove the `FieldLayout::initial_saved_value_`
that was present for both static and non-static fields. In reality this
initial saved value is only meaningful for static fields though it was
kept in memory as well as (de)serialized even for non-static fields.
The one place where it was actually used for non-static fields was
incorrect and should instead use `null`.
The removal of this field results in net removal of code in this CL.
Issue https://github.com/dart-lang/sdk/issues/36097
TEST=Internal refactoring, relying on existing test coverage.
Change-Id: I088a87e2ea159bac7fa7f1f360da553d752e6569
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/173263
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>
This reverts commit 922ea3e9b6 in patchset 1, fix for assertion triggered in https://ci.chromium.org/b/8883214567628884960 in patchset 2, fix for deadlock around symbols table mutex in patchset 4.
Original commit description:
Speed up is achieved by sharing most of the dart code, object store
and class table between isolates in single isolate group. So
instead of bootstrapping isolate from the snapshot, isolate is
initialized by setting pointers to existing data structures already
set up for first isolate, and only few isolate-specific structures (moved
to newly introducted isolate_object_store) are created.
To allow for safe cross-isolate switchable call site, type test cache
mutations additional synchronization via RunWithStoppedMutators(that
relies on safepoints) was added.
Besides switchable call sites, no other mutation to the dart code is
done in AOT, which allows such sharing.
Bug: https://github.com/dart-lang/sdk/issues/37835
Bug: https://github.com/dart-lang/sdk/issues/36097
Change-Id: I655e337198214c9dfacbe76f7852b941b5a7e910
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143462
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Original revert in patchset 1, fix for deadlock issue in patchset 2: avoid reentrant calls to RunWithStoppedMutator.
Further review comments addressed in successive patchsets.
This reverts commit 8ef508ba36.
Original commit description:
Speed up is achieved by sharing most of the dart code, object store
and class table between isolates in single isolate group. So
instead of bootstrapping isolate from the snapshot, isolate is
initialized by setting pointers to existing data structures already
set up for first isolate, and only few isolate-specific structures (moved
to newly introducted isolate_object_store) are created.
To allow for safe cross-isolate switchable call site, type test cache
mutations additional synchronization via RunWithStoppedMutators(that
relies on safepoints) was added.
Besides switchable call sites, no other mutation to the dart code is
done in AOT, which allows such sharing.
Change-Id: I6a0279d9812020ad7a5c2b7851980b6a29b95b9a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/143327
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Speed up is achieved by sharing most of the dart code, object store
and class table between isolates in single isolate group. So
instead of bootstrapping isolate from the snapshot, isolate is
initialized by setting pointers to existing data structures already
set up for first isolate, and only few isolate-specific structures (moved
to newly introducted isolate_object_store) are created.
To allow for safe cross-isolate switchable call site, type test cache
mutations additional synchronization via RunWithStoppedMutators(that
relies on safepoints) was added.
Besides switchable call sites, no other mutation to the dart code is
done in AOT, which allows such sharing.
Bug: https://github.com/dart-lang/sdk/issues/37835
Bug: https://github.com/dart-lang/sdk/issues/36097
Change-Id: I64c86525f4ef9cb30567a49a106bfe700355942b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136780
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Martin Kustermann