Ivan Inozemtsev
51ea42537a
Also add a sample for calling Dart functions which return/accept futures. Change-Id: I932d0577709f4e068ccd3212797751ecb347c4f9 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/408281 Commit-Queue: Ivan Inozemtsev <iinozemtsev@google.com> Reviewed-by: Martin Kustermann <kustermann@google.com>
Dart Engine
The include/dart_engine.h provides additional functions to embed the Dart VM
and to call Dart functions from kernel and AOT snapshots. It is not intended to
be a full-featured API, and should be used together with dart_api.h.
It is intended for reusing of existing Dart code in non-Dart programs, and allows to use Dart snapshots as shared libraries: the caller can start one or several isolates from Dart snapshots and call Dart functions from it.
Comparing to dart_api.h it brings the following:
- Full initialization of Dart VM, including initializing core libraries.
- Easier handling of isolate messages
- Lock-guarded functions to enter/exit isolates.
See examples in samples/embedder for usages of the API.
Handling isolate messages
In dart_api.h there are two possible ways to handle asynchronous
isolate messages:
Dart_MessageNotifyCallback: Users can pass a callback to get notifications about messages to handle, but handling messages still requires entering an isolate, entering a scope, callingDart_HandleMessage, and then leaving a scope and an isolate.Dart_RunLoop: Users can invoke it on a separate thread, but then they won't be able to enter isolates from other threads.
As an alternative, dart_engine.h provides a simpler function
DartEngine_HandleMessage, which encapsulates isolate and scope management, and
it allows to specify per isolate / default message schedulers, which only need
to schedule an execution DartEngine_HandleMessage with the right isolate.
Users can create their own DartEngine_MessageScheduler struct and pass it to
DartEngine_SetMessageScheduler / DartEngine_SetDefaultMessageScheduler. See
samples/embedder/run_timer_async.cc and samples/embedder/run_timer.cc
examples.
Entering / leaving isolates
Because engine API uses its own message handling, it is important to use
DartEngine_AcquireIsolate / DartEngine_ReleaseIsolate instead of
Dart_EnterIsolate / Dart_ExitIsolate. DartEngine_AcquireIsolate blocks
until an isolate can be entered by trying to obtain an internal lock (which is
released by DartEngine_ReleaseIsolate), while Dart_EnterIsolate crashes if
some other thread has entered the same isolate.