Building image encoding into the engine bloated the
binary size. This change will return raw bytes, and
callers who use this functionality can take on the
dependency on image encoding in their apps (via a
Dart package or a platform plugin).
Fixes https://github.com/flutter/flutter/issues/16537
* 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
* Revert "Add support for measuring, combining, and getting bounds of Path objects (#4799)"
This reverts commit 8c00101a59cd16c30d51663b58c6f2ee9ee2e2b9, as it broke engine build bots on Linux and Windows.
* add path measure
* fix typo
* getBound and addPathWithMatrix
* Add myself to Authors, add PathOps
* fix linting issues
* update licenses_flutter to add new files
* Use matrix4 instead of matrix3 for consistency/interop
* put pubspec back
* fix bug in getSegment
* fix typo
* Add return value for PathOp
* refactoring from review
* refactoring from review - still TBD on computeMetrics()
* add doc
* lint issue
* fix computeMetrics, add Path.from
* add missing wireup for clone
* change PathMetrics to iterable, fix bug with angle on Tangent
* prefer std::make_unique
* cleanup docs
* add path measure
* fix typo
* getBound and addPathWithMatrix
* Add myself to Authors, add PathOps
* fix linting issues
* update licenses_flutter to add new files
* Use matrix4 instead of matrix3 for consistency/interop
* put pubspec back
* fix bug in getSegment
* fix typo
* Add return value for PathOp
* refactoring from review
* refactoring from review - still TBD on computeMetrics()
* add doc
* lint issue
* fix computeMetrics, add Path.from
* add missing wireup for clone
* change PathMetrics to iterable, fix bug with angle on Tangent
* prefer std::make_unique
* cleanup docs
* fix iterator bug
* remove unnecessary clone for computeMetrics
* fix some doc issues
* fix PathMeasure iterator, extendWithPath, isClosed, and pubspec.lock
* get rid of orElse; use StateException
* StateError, not StateException
* doc improvements and nits
* add unit tests, fix bugs found during testing
* fix two uncommited doc changes
* one more
* change sign of tangent angle, update docs
* update unit tests for inverted angle
* update tangent to include vector
* Doc fixes
gtest is an old version that predates the googletest and googlemock
merger, all tests should be using the newer googletest that's being
kept in sync with the upstream version.
gtest is an old version that predates the googletest and googlemock
merger, all tests should be using the newer googletest that's being
kept in sync with the upstream version.
Window.viewInsets is the set of window-relative insets that describe the
area of the window that an application may want to treat as effectively
reducing the size of the content. Typically this is due to system UI
that fully obscures underlying content, such as the keyboard.
This area differs from padding in that padding is the set of insets that
describe the area of the window that may be partially (or fully)
obscured by system UI or physical intrusions into the view area (e.g.
iPhone X sensor housing, status bar, or the iPhone X home indicator
widget).
This patch does not yet enable the iOS bottom edge safe area. Once the
framework has been updated to use viewInsets for bottom-edge occlusions
(today, the keyboard), the bottom safe area will be enabled and
framework patches that depend on it, landed.
This is the first step to support animated GIFs: flutter/flutter#204
TBD in following CLs:
* Implement Codec.getNextFrame.
* Add Framework side support to run animations.
Previously, cases like:
```dart
Color.lerp(const Color(0xFF00FF7F), const Color(0xFF00FFFF), 1.1)
```
...would result in unexpected effects (in this instance, lerping
between these colors with a curve that overshoots would take what
should be a simple animation from pale green to blue and add some
flickering bright green whenever it overshoots).
* preserve Window callback zones
Run Window callbacks in the zone they are registered in. This is consistent with how other native API work, such as `scheduleMicrotask`, `Timer`, and `dart:io`. This also enables the developers to use the `Zone` API to capture and log unhandled Dart errors.
* refactor wrapping
* new line
* fewer if checks; group getters/setters/fields
* inline _invokeOnPointerDataPacket
This attempts to make the Canvas API and some related features more
likely to throw a Dart exception than crash when exposed to bad input.
Depends on rolling tonic to
https://fuchsia-review.googlesource.com/c/35742/ which this patch does
not yet do, but I wanted to put it up for review to see if it was even
a reasonable approach.
