- 24 8月, 2019 1 次提交
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由 Chinmay Garde 提交于
We will end up creating fewer threads in tests.
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- 06 8月, 2019 1 次提交
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由 Chinmay Garde 提交于
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- 10 7月, 2019 1 次提交
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由 Chinmay Garde 提交于
This patch reworks image decompression and collection in the following ways because of misbehavior in the described edge cases. The current flow for realizing a texture on the GPU from a blob of compressed bytes is to first pass it to the IO thread for image decompression and then upload to the GPU. The handle to the texture on the GPU is then passed back to the UI thread so that it can be included in subsequent layer trees for rendering. The GPU contexts on the Render & IO threads are in the same sharegroup so the texture ends up being visible to the Render Thread context during rendering. This works fine and does not block the UI thread. All references to the image are owned on UI thread by Dart objects. When the final reference to the image is dropped, the texture cannot be collected on the UI thread (because it has not GPU context). Instead, it must be passed to either the GPU or IO threads. The GPU thread is usually in the middle of a frame workload so we redirect the same to the IO thread for eventual collection. While texture collections are usually (comparatively) fast, texture decompression and upload are slow (order of magnitude of frame intervals). For application that end up creating (by not necessarily using) numerous large textures in straight-line execution, it could be the case that texture collection tasks are pending on the IO task runner after all the image decompressions (and upload) are done. Put simply, the collection of the first image could be waiting for the decompression and upload of the last image in the queue. This is exacerbated by two other hacks added to workaround unrelated issues. * First, creating a codec with a single image frame immediately kicks of decompression and upload of that frame image (even if the frame was never request from the codec). This hack was added because we wanted to get rid of the compressed image allocation ASAP. The expectation was codecs would only be created with the sole purpose of getting the decompressed image bytes. However, for applications that only create codecs to get image sizes (but never actually decompress the same), we would end up replacing the compressed image allocation with a larger allocation (device resident no less) for no obvious use. This issue is particularly insidious when you consider that the codec is usually asked for the native image size first before the frame is requested at a smaller size (usually using a new codec with same data but new targetsize). This would cause the creation of a whole extra texture (at 1:1) when the caller was trying to “optimize” for memory use by requesting a texture of a smaller size. * Second, all image collections we delayed in by the unref queue by 250ms because of observations that the calling thread (the UI thread) was being descheduled unnecessarily when a task with a timeout of zero was posted from the same (recall that a task has to be posted to the IO thread for the collection of that texture). 250ms is multiple frame intervals worth of potentially unnecessary textures. The net result of these issues is that we may end up creating textures when all that the application needs is to ask it’s codec for details about the same (but not necessarily access its bytes). Texture collection could also be delayed behind other jobs to decompress the textures on the IO thread. Also, all texture collections are delayed for an arbitrary amount of time. These issues cause applications to be susceptible to OOM situations. These situations manifest in various ways. Host memory exhaustion causes the usual OOM issues. Device memory exhaustion seems to manifest in different ways on iOS and Android. On Android, allocation of a new texture seems to be causing an assertion (in the driver). On iOS, the call hangs (presumably waiting for another thread to release textures which we won’t do because those tasks are blocked behind the current task completing). To address peak memory usage, the following changes have been made: * Image decompression and upload/collection no longer happen on the same thread. All image decompression will now be handled on a workqueue. The number of worker threads in this workqueue is equal to the number of processors on the device. These threads have a lower priority that either the UI or Render threads. These workers are shared between all Flutter applications in the process. * Both the images and their codec now report the correct allocation size to Dart for GC purposes. The Dart VM uses this to pick objects for collection. Earlier the image allocation was assumed to 32bpp with no mipmapping overhead reported. Now, the correct image size is reported and the mipmapping overhead is accounted for. Image codec sizes were not reported to the VM earlier and now are. Expect “External” VM allocations to be higher than previously reported and the numbers in Observatory to line up more closely with actual memory usage (device and host). * Decoding images to a specific size used to decode to 1:1 before performing a resize to the correct dimensions before texture upload. This has now been reworked so that images are first decompressed to a smaller size supported natively by the codec before final resizing to the requested target size. The intermediate copy is now smaller and more promptly collected. Resizing also happens on the workqueue worker. * The drain interval of the unref queue is now sub-frame-interval. I am hesitant to remove the delay entirely because I have not been able to instrument the performance overhead of the same. That is next on my list. But now, multiple frame intervals worth of textures no longer stick around. The following issues have been addressed: * https://github.com/flutter/flutter/issues/34070 Since this was the first usage of the concurrent message loops, the number of idle wakes were determined to be too high and this component has been rewritten to be simpler and not use the existing task runner and MessageLoopImpl interface. * Image decoding had no tests. The new `ui_unittests` harness has been added that sets up a GPU test harness on the host using SwiftShader. Tests have been added for image decompression, upload and resizing. * The device memory exhaustion in this benchmark has been addressed. That benchmark is still not viable for inclusion in any harness however because it creates 9 million codecs in straight-line execution. Because these codecs are destroyed in the microtask callbacks, these are referenced till those callbacks are executed. So now, instead of device memory exhaustion, this will lead to (slower) exhaustion of host memory. This is expected and working as intended. This patch only addresses peak memory use and makes collection of unused images and textures more prompt. It does NOT address memory use by images referenced strongly by the application or framework.
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- 21 4月, 2019 1 次提交
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由 Chinmay Garde 提交于
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- 30 3月, 2019 1 次提交
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由 Chinmay Garde 提交于
Previously, only the most basic tests were run in AOT mode.
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- 08 11月, 2018 1 次提交
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由 Michael Goderbauer 提交于
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- 27 7月, 2018 1 次提交
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由 Chinmay Garde 提交于
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- 14 4月, 2018 1 次提交
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由 Chinmay Garde 提交于
* Re-land "Support multiple shells in a single process. (#4932)" This reverts commit 723c7d01.
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- 13 4月, 2018 1 次提交
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由 Vyacheslav Egorov 提交于
This reverts commit a3327bff.
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- 12 4月, 2018 1 次提交
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由 Chinmay Garde 提交于
This reverts commit 9199b40f.
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- 11 4月, 2018 2 次提交
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由 Chinmay Garde 提交于
This reverts commit 6baff4c8.
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由 Chinmay Garde 提交于
* 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
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