// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef INCLUDE_CPPGC_PLATFORM_H_
#define INCLUDE_CPPGC_PLATFORM_H_
#include <memory>
#include "cppgc/source-location.h"
#include "v8-platform.h" // NOLINT(build/include_directory)
#include "v8config.h" // NOLINT(build/include_directory)
namespace cppgc {
// TODO(v8:10346): Create separate includes for concepts that are not
// V8-specific.
using IdleTask = v8::IdleTask;
using JobHandle = v8::JobHandle;
using JobDelegate = v8::JobDelegate;
using JobTask = v8::JobTask;
using PageAllocator = v8::PageAllocator;
using Task = v8::Task;
using TaskPriority = v8::TaskPriority;
using TaskRunner = v8::TaskRunner;
using TracingController = v8::TracingController;
/**
* Platform interface used by Heap. Contains allocators and executors.
*/
class V8_EXPORT Platform {
public:
virtual ~Platform() = default;
/**
* \returns the allocator used by cppgc to allocate its heap and various
* support structures. Returning nullptr results in using the `PageAllocator`
* provided by `cppgc::InitializeProcess()` instead.
*/
virtual PageAllocator* GetPageAllocator() = 0;
/**
* Monotonically increasing time in seconds from an arbitrary fixed point in
* the past. This function is expected to return at least
* millisecond-precision values. For this reason,
* it is recommended that the fixed point be no further in the past than
* the epoch.
**/
virtual double MonotonicallyIncreasingTime() = 0;
/**
* Foreground task runner that should be used by a Heap.
*/
virtual std::shared_ptr<TaskRunner> GetForegroundTaskRunner() {
return nullptr;
}
/**
* Posts `job_task` to run in parallel. Returns a `JobHandle` associated with
* the `Job`, which can be joined or canceled.
* This avoids degenerate cases:
* - Calling `CallOnWorkerThread()` for each work item, causing significant
* overhead.
* - Fixed number of `CallOnWorkerThread()` calls that split the work and
* might run for a long time. This is problematic when many components post
* "num cores" tasks and all expect to use all the cores. In these cases,
* the scheduler lacks context to be fair to multiple same-priority requests
* and/or ability to request lower priority work to yield when high priority
* work comes in.
* A canonical implementation of `job_task` looks like:
* \code
* class MyJobTask : public JobTask {
* public:
* MyJobTask(...) : worker_queue_(...) {}
* // JobTask implementation.
* void Run(JobDelegate* delegate) override {
* while (!delegate->ShouldYield()) {
* // Smallest unit of work.
* auto work_item = worker_queue_.TakeWorkItem(); // Thread safe.
* if (!work_item) return;
* ProcessWork(work_item);
* }
* }
*
* size_t GetMaxConcurrency() const override {
* return worker_queue_.GetSize(); // Thread safe.
* }
* };
*
* // ...
* auto handle = PostJob(TaskPriority::kUserVisible,
* std::make_unique<MyJobTask>(...));
* handle->Join();
* \endcode
*
* `PostJob()` and methods of the returned JobHandle/JobDelegate, must never
* be called while holding a lock that could be acquired by `JobTask::Run()`
* or `JobTask::GetMaxConcurrency()` -- that could result in a deadlock. This
* is because (1) `JobTask::GetMaxConcurrency()` may be invoked while holding
* internal lock (A), hence `JobTask::GetMaxConcurrency()` can only use a lock
* (B) if that lock is *never* held while calling back into `JobHandle` from
* any thread (A=>B/B=>A deadlock) and (2) `JobTask::Run()` or
* `JobTask::GetMaxConcurrency()` may be invoked synchronously from
* `JobHandle` (B=>JobHandle::foo=>B deadlock).
*
* A sufficient `PostJob()` implementation that uses the default Job provided
* in libplatform looks like:
* \code
* std::unique_ptr<JobHandle> PostJob(
* TaskPriority priority, std::unique_ptr<JobTask> job_task) override {
* return std::make_unique<DefaultJobHandle>(
* std::make_shared<DefaultJobState>(
* this, std::move(job_task), kNumThreads));
* }
* \endcode
*/
virtual std::unique_ptr<JobHandle> PostJob(
TaskPriority priority, std::unique_ptr<JobTask> job_task) {
return nullptr;
}
/**
* Returns an instance of a `TracingController`. This must be non-nullptr. The
* default implementation returns an empty `TracingController` that consumes
* trace data without effect.
*/
virtual TracingController* GetTracingController();
};
/**
* Process-global initialization of the garbage collector. Must be called before
* creating a Heap.
*
* Can be called multiple times when paired with `ShutdownProcess()`.
*
* \param page_allocator The allocator used for maintaining meta data. Must stay
* always alive and not change between multiple calls to InitializeProcess. If
* no allocator is provided, a default internal version will be used.
* \param desired_heap_size Desired amount of virtual address space to reserve
* for the heap, in bytes. Actual size will be clamped to minimum and maximum
* values based on compile-time settings and may be rounded up. If this
* parameter is zero, a default value will be used.
*/
V8_EXPORT void InitializeProcess(PageAllocator* page_allocator = nullptr,
size_t desired_heap_size = 0);
/**
* Must be called after destroying the last used heap. Some process-global
* metadata may not be returned and reused upon a subsequent
* `InitializeProcess()` call.
*/
V8_EXPORT void ShutdownProcess();
namespace internal {
V8_EXPORT void Fatal(const std::string& reason = std::string(),
const SourceLocation& = SourceLocation::Current());
} // namespace internal
} // namespace cppgc
#endif // INCLUDE_CPPGC_PLATFORM_H_
