This reverts commit 19ebd61442fd3bf6a69af2156c8b118fc8578ec2.
Additionally, the following _flutter.runInView deadlock is fixed.
Previously, a deadlock would occur when service protocol
_flutter.runInView is used to restart the engine wihtout tearing down
the shell: the shared mutex of the service protocol will be locked
during the restart as it's in the middle of handling a service protocol
message; if ServiceProtocol::AddHandler is also called during the
restart, the deadlock happens as AddHandler also requires such lock.
test/integration.shard/background_isolate_test.dart would fail
without this fix.
## Description
As the related issue refer, the application may be doing too much work on its main thread even in a simple hello_world demo.
That is because the creation of `Engine` on the ui thread takes a noticeable time, and it is blocking the platform thread in order to run `Shell::Setup` synchronously.
The cost of `Engine`'s constructor is mainly about the creating of root isolate. Actually, there used to be another time-consuming process, the default font manager setup, which was resolved by https://github.com/flutter/engine/pull/18225.
Similar to https://github.com/flutter/engine/pull/18225, this pr move the creation of root isolate out from creating `Engine`. After this action, the main thread blocking is quite an acceptable slice.
## Related Issues
https://github.com/flutter/flutter/issues/40563 could be resolved by this pr.
Using it, a Flutter app can monitor missing frames in the release mode, and a custom Flutter runner (e.g., Fuchsia) can add a custom FrameRasterizedCallback.
Related issues:
https://github.com/flutter/flutter/issues/26154https://github.com/flutter/flutter/issues/31444https://github.com/flutter/flutter/issues/32447
Need review as soon as possible so we can merge this before the end of May to catch the milestone.
Tests added:
* NoNeedToReportTimingsByDefault
* NeedsReportTimingsIsSetWithCallback
* ReportTimingsIsCalled
* FrameRasterizedCallbackIsCalled
* FrameTimingSetsAndGetsProperly
* onReportTimings preserves callback zone
* FrameTiming.toString has the correct format
This will need a manual engine roll as the TestWindow defined in the framework needs to implement onReportTimings.
Some components in the Flutter engine were derived from the forked blink codebase. While the forked components have either been removed or rewritten, the use of the blink namespace has mostly (and inconsistently) remained. This renames the blink namesapce to flutter for consistency. There are no functional changes in this patch.
The service protocol's ListViews method needs to return description data for
each engine in the process. Previously ListViews would queue a task to each
UI thread to gather this data. However, the UI thread might be blocked from
executing tasks (e.g. if the Dart isolate is paused), resulting in a deadlock.
This change provides a copy of the engine's description data to the
ServiceProtocol's global list of engines, allowing ListViews to run without
accessing any UI threads.
Fixes https://github.com/flutter/flutter/issues/24400
* Support multiple shells in a single process.
The Flutter Engine currently works by initializing a singleton shell
instance. This shell has to be created on the platform thread. The shell
is responsible for creating the 3 main threads used by Flutter (UI, IO,
GPU) as well as initializing the Dart VM. The shell, references to task
runners of the main threads as well as all snapshots used for VM
initialization are stored in singleton objects. The Flutter shell only
creates the threads, rasterizers, contexts, etc. to fully support a
single Flutter application. Current support for multiple Flutter
applications is achieved by making multiple applications share the same
resources (via the platform views mechanism).
This scheme has the following limitations:
* The shell is a singleton and there is no way to tear it down. Once you
run a Flutter application in a process, all resources managed by it
will remain referenced till process termination.
* The threads on which the shell performs its operations are all
singletons. These threads are never torn down and multiple Flutter
applications (if present) have to compete with one another on these
threads.
* Resources referenced by the Dart VM are leaked because the VM isn't
shutdown even when there are no more Flutter views.
* The shell as a target does not compile on Fuchsia. The Fuchsia content
handler uses specific dependencies of the shell to rebuild all the
shell dependencies on its own. This leads to differences in frame
scheduling, VM setup, service protocol endpoint setup, tracing, etc..
Fuchsia is very much a second class citizen in this world.
* Since threads and message loops are managed by the engine, the engine
has to know about threading and platform message loop interop on each
supported platform.
Specific updates in this patch:
* The shell is no longer a singleton and the embedder holds the unique
reference to the shell.
* Shell setup and teardown is deterministic.
* Threads are no longer managed by the shell. Instead, the shell is
given a task runner configuration by the embedder.
* Since the shell does not own its threads, the embedder can control
threads and the message loops operating on these threads. The shell is
only given references to the task runners that execute tasks on these
threads.
* The shell only needs task runner references. These references can be
to the same task runner. So, if the embedder thinks that a particular
Flutter application would not need all the threads, it can pass
references to the same task runner. This effectively makes Flutter
application run in single threaded mode. There are some places in the
shell that make synchronous calls, these sites have been updated to
ensure that they don’t deadlock.
* The test runner and the headless Dart code runner are now Flutter
applications that are effectively single threaded (since they don’t
have rendering concerns of big-boy Flutter application).
* The embedder has to guarantee that the threads and outlive the shell.
It is easy for the embedder to make that guarantee because shell
termination is deterministic.
* The embedder can create as many shell as it wants. Typically it
creates a shell per Flutter application with its own task runner
configuration. Most embedders obtain these task runners from threads
dedicated to the shell. But, it is entirely possible that the embedder
can obtain these task runners from a thread pool.
* There can only be one Dart VM in the process. The numerous shell
interact with one another to manage the VM lifecycle. Once the last
shell goes away, the VM does as well and hence all resources
associated with the VM are collected.
* The shell as a target can now compile and run on Fuchsia. The current
content handler has been removed from the Flutter engine source tree
and a new implementation has been written that uses the new shell
target.
* Isolate management has been significantly overhauled. There are no
owning references to Dart isolates within the shell. The VM owns the
only strong reference to the Dart isolate. The isolate that has window
bindings is now called the root isolate. Child isolates can now be
created from the root isolate and their bindings and thread
configurations are now inherited from the root isolate.
* Terminating the shell terminates its root isolates as well as all the
isolates spawned by this isolate. This is necessary be shell shutdown
is deterministic and the embedder is free to collect the threads on
which the isolates execute their tasks (and listen for mircrotasks
flushes on).
* Launching the root isolate is now significantly overhauled. The shell
side (non-owning) reference to an isolate is now a little state
machine and illegal state transitions should be impossible (barring
construction issues). This is the only way to manage Dart isolates in
the shell (the shell does not use the C API is dart_api.h anymore).
* Once an isolate is launched, it must be prepared (and hence move to
the ready phase) by associating a snapshot with the same. This
snapshot can either be a precompiled snapshot, kernel snapshot, script
snapshot or source file. Depending on the kind of data specified as a
snapshot as well as the capabilities of the VM running in the process,
isolate preparation can fail preparation with the right message.
* Asset management has been significantly overhauled. All asset
resolution goes through an abstract asset resolver interface. An asset
manager implements this interface and manages one or more child asset
resolvers. These asset resolvers typically resolve assets from
directories, ZIP files (legacy FLX assets if provided), APK bundles,
FDIO namespaces, etc…
* Each launch of the shell requires a separate and fully configured
asset resolver. This is necessary because launching isolates for the
engine may require resolving snapshots as assets from the asset
resolver. Asset resolvers can be shared by multiple launch instances
in multiple shells and need to be thread safe.
* References to the command line object have been removed from the
shell. Instead, the shell only takes a settings object that may be
configured from the command line. This makes it easy for embedders and
platforms that don’t have a command line (Fuchsia) to configure the
shell. Consequently, there is only one spot where the various switches
are read from the command line (by the embedder and not the shell) to
form the settings object.
* All platform now respect the log tag (this was done only by Android
till now) and each shell instance have its own log tag. This makes
logs from multiple Flutter application in the same process (mainly
Fuchsia) more easily decipherable.
* The per shell IO task runner now has a new component that is
unfortunately named the IOManager. This component manages the IO
GrContext (used for asynchronous texture uploads) that cooperates with
the GrContext on the GPU task runner associated with the shell. The
IOManager is also responsible for flushing tasks that collect Skia
objects that reference GPU resources during deterministic shell
shutdown.
* The embedder now has to be careful to only enable Blink on a single
instance of the shell. Launching the legacy text layout and rendering
engine multiple times is will trip assertions. The entirety of this
runtime has been separated out into a separate object and can be
removed in one go when the migration to libtxt is complete.
* There is a new test target for the various C++ objects that the shell
uses to interact with the Dart VM (the shell no longer use the C API
in dart_api.h). This allows engine developers to test VM/Isolate
initialization and teardown without having the setup a full shell
instance.
* There is a new test target for the testing a single shell instances
without having to configure and launch an entire VM and associated
root isolate.
* Mac, Linux & Windows used to have different target that created the
flutter_tester referenced by the tool. This has now been converted
into a single target that compiles on all platforms.
* WeakPointers vended by the fml::WeakPtrFactory(notice the difference
between the same class in the fxl namespace) add threading checks on
each use. This is enabled by getting rid of the “re-origination”
feature of the WeakPtrFactory in the fxl namespace. The side effect of
this is that all non-thread safe components have to be created, used
and destroyed on the same thread. Numerous thread safety issues were
caught by this extra assertion and have now been fixed.
* Glossary of components that are only safe on a specific thread (and
have the fml variants of the WeakPtrFactory):
* Platform Thread: Shell
* UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator
* GPU Thread: Rasterizer, Surface
* IO Thread: IOManager
This patch was reviewed in smaller chunks in the following pull
requests. All comments from the pulls requests has been incorporated
into this patch:
* flutter/assets: https://github.com/flutter/engine/pull/4829
* flutter/common: https://github.com/flutter/engine/pull/4830
* flutter/content_handler: https://github.com/flutter/engine/pull/4831
* flutter/flow: https://github.com/flutter/engine/pull/4832
* flutter/fml: https://github.com/flutter/engine/pull/4833
* flutter/lib/snapshot: https://github.com/flutter/engine/pull/4834
* flutter/lib/ui: https://github.com/flutter/engine/pull/4835
* flutter/runtime: https://github.com/flutter/engine/pull/4836
* flutter/shell: https://github.com/flutter/engine/pull/4837
* flutter/synchronization: https://github.com/flutter/engine/pull/4838
* flutter/testing: https://github.com/flutter/engine/pull/4839
The UIDartState is now always owned by the isolate and always freed in
the isolate cleanup callback.
In the isolate shutdown callback, if the isolate being shut down is the
main isolate, the RuntimeController is informed which in turn notifies
the RuntimeHolder and thus the ApplicationControllerImpl. The
ApplicationControllerImpl tears down the whole Flutter application.
This fixes Fuchsia bug: MI4-328
After this patch, platform messages now take the same path through the system
that semantics data does (on Android). Support on iOS will be in another patch.
This patch prepares us to switch sending semantics information over mojom to
using dart:ui directly. Currently the recorded information is dropped on the
floor, but that will improve in future patches.
Also, rename SkyViewClient to RuntimeDelegate. These names are more
sensible.
This patch also cleans up the RuntimeDelegate a bit, for example by
removing support for flushing real-time events, which aren't used.
