In cases where a valid IsolateConfiguration cannot be inferred, (e.g.,
settings.kernel_list_asset is missing) RunConfiguration can be created
with a null IsolateConfiguration. In such cases, bail out early with
kInvalidSettings.
Also adds a redundant paranoid check to EmbedderEngine::Run.
As of the migration to Dart 2, it has been necessary to compile Dart to
kernel prior to execution. The embedder currently requires that the
resulting kernel file be named `kernel_blob.bin` and be located at the
root of the assets directory passed to the embedder API.
This patch updates the test_fixtures build rule to perform a kernel
compile using frontend_server, outputting `kernel_blob.bin` to
`fixtures/test_target_name` directory, and updates the embedder
unittests to specify the kernel file rather than the Dart source file.
Since the kernel compiler requires a `main()` function to be defined, it
also updates `simple_main.dart` from runtime_unittests to define
`main()` rather than `simple_main()`.
This also updates all existing sub-targets to be testonly.
This relands commit ac9e521a1ddbb99816a93d92ce9fb70e950b3763, which was
reverted in commit 494112582932af98b282617d7a34b1fbb8c90307. Rather than
running as prebuilt_dart_action, we use dart_action to ensure the
frontend snapshot it compatible with the VM on which it's executed.
This reverts commit ac9e521a1ddbb99816a93d92ce9fb70e950b3763.
This broke dynamic release mode builds of
//flutter/runtime:runtime_fixtures_kernel (likely all product-mode
builds).
Compile embedder unit test Dart to kernel
As of the migration to Dart 2, it has been necessary to compile Dart to
kernel prior to execution. The embedder currently requires that the
resulting kernel file be named `kernel_blob.bin` and be located at the
root of the assets directory passed to the embedder API.
This patch updates the test_fixtures build rule to perform a kernel
compile using frontend_server, outputting `kernel_blob.bin` to
`fixtures/test_target_name` directory, and updates the embedder
unittests to specify the kernel file rather than the Dart source file.
Since the kernel compiler requires a `main()` function to be defined, it
also updates `simple_main.dart` from runtime_unittests to define
`main()` rather than `simple_main()`.
This also updates all existing sub-targets to be testonly.
Reduces spurious error log messages in GLContextMakeCurrent() attempting
set up the GR context:
[ERROR:flutter/shell/gpu/gpu_surface_gl.cc(42)] Could not make the context current to setup the gr context.
- Switch core snapshot to Dart 2 and remove support for loading platform.dill.
- Remove support for loading script snapshots.
- Remove support for loading source.
- Remove settings and fix names to reflect the above.
- Remove support for loading the service isolate from source.
This allows the stable header to be referenced from a known location. Also reduces the visibility of the framework target so that it is automatically built on the mac.
These snapshots used to be included (from the runtime target) in the executable if AOT mode was disabled. The mobile shells now include this snapshot in the kernel snapshot generated on the host. However the target that run on the host still need this. The tester target was already patched but the desktop embedder targets were overlooked. The unit tests passed on the embedder target because the unit tester exectuable was including the snapshot in addition to the dylib. Now the dylib itself depends on the snapshot directly.
Creating a dylib from a “complete” static library does not propagate symbol visisbility definitions. I also got rid of the static library and used a source set instead because we don’t need to do the extra work for other targets.
"flutter build bundle" in Dart 2 mode now builds an assets directory
containing the application and platform kernels along with the app's other
assets.
With this patch, embedders can run these bundles by setting
FlutterProjectArgs.assets_path to the bundle directory. In this scenario,
FlutterProjectArgs.main_path and packages_path will be ignored.
* 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
