v8/include/v8-platform.h
Andreas Haas c690f54d95 [platform] Add TaskRunner to the platform API
With the existing platform API it is not possible to post foreground
tasks from background tasks. This is, however, required to implement
asynchronous compilation for WebAssembly. With this CL we add the
concept of a TaskRunner to the platform API. The TaskRunner contains
all data needed to post a foreground task and can be used both from a
foreground task and a background task. Eventually the TaskRunner should
replace the existing API.

In addition, this CL contains a default implementation of the
TaskRunner. This implementation has tempory workaround for platforms
which do not provide a TaskRunner implementation yet. This default
implementation should be deleted again when all platforms provide a
TaskRunner implementation.

R=rmcilroy@chromium.org

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I6ea4a1c9da1eb9a19e8ce8f2163000dbc2598802
Reviewed-on: https://chromium-review.googlesource.com/741588
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49041}
2017-10-30 16:17:08 +00:00

306 lines
10 KiB
C++

// Copyright 2013 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 V8_V8_PLATFORM_H_
#define V8_V8_PLATFORM_H_
#include <stddef.h>
#include <stdint.h>
#include <memory>
#include <string>
namespace v8 {
class Isolate;
/**
* A Task represents a unit of work.
*/
class Task {
public:
virtual ~Task() = default;
virtual void Run() = 0;
};
/**
* An IdleTask represents a unit of work to be performed in idle time.
* The Run method is invoked with an argument that specifies the deadline in
* seconds returned by MonotonicallyIncreasingTime().
* The idle task is expected to complete by this deadline.
*/
class IdleTask {
public:
virtual ~IdleTask() = default;
virtual void Run(double deadline_in_seconds) = 0;
};
/**
* A TaskRunner allows scheduling of tasks. The TaskRunner may still be used to
* post tasks after the isolate gets destructed, but these tasks may not get
* executed anymore. All tasks posted to a given TaskRunner will be invoked in
* sequence. Tasks can be posted from any thread.
*/
class TaskRunner {
public:
/**
* Schedules a task to be invoked by this TaskRunner. The TaskRunner
* implementation takes ownership of |task|.
*/
virtual void PostTask(std::unique_ptr<Task> task) = 0;
/**
* Schedules a task to be invoked by this TaskRunner. The task is scheduled
* after the given number of seconds |delay_in_seconds|. The TaskRunner
* implementation takes ownership of |task|.
*/
virtual void PostDelayedTask(std::unique_ptr<Task> task,
double delay_in_seconds) = 0;
/**
* Schedules an idle task to be invoked by this TaskRunner. The task is
* scheduled when the embedder is idle. Requires that
* TaskRunner::SupportsIdleTasks(isolate) is true. Idle tasks may be reordered
* relative to other task types and may be starved for an arbitrarily long
* time if no idle time is available. The TaskRunner implementation takes
* ownership of |task|.
*/
virtual void PostIdleTask(std::unique_ptr<IdleTask> task) = 0;
/**
* Returns true if idle tasks are enabled for this TaskRunner.
*/
virtual bool IdleTasksEnabled() = 0;
TaskRunner() = default;
virtual ~TaskRunner() = default;
private:
TaskRunner(const TaskRunner&) = delete;
TaskRunner& operator=(const TaskRunner&) = delete;
};
/**
* The interface represents complex arguments to trace events.
*/
class ConvertableToTraceFormat {
public:
virtual ~ConvertableToTraceFormat() = default;
/**
* Append the class info to the provided |out| string. The appended
* data must be a valid JSON object. Strings must be properly quoted, and
* escaped. There is no processing applied to the content after it is
* appended.
*/
virtual void AppendAsTraceFormat(std::string* out) const = 0;
};
/**
* V8 Tracing controller.
*
* Can be implemented by an embedder to record trace events from V8.
*/
class TracingController {
public:
virtual ~TracingController() = default;
/**
* Called by TRACE_EVENT* macros, don't call this directly.
* The name parameter is a category group for example:
* TRACE_EVENT0("v8,parse", "V8.Parse")
* The pointer returned points to a value with zero or more of the bits
* defined in CategoryGroupEnabledFlags.
**/
virtual const uint8_t* GetCategoryGroupEnabled(const char* name) {
static uint8_t no = 0;
return &no;
}
/**
* Adds a trace event to the platform tracing system. This function call is
* usually the result of a TRACE_* macro from trace_event_common.h when
* tracing and the category of the particular trace are enabled. It is not
* advisable to call this function on its own; it is really only meant to be
* used by the trace macros. The returned handle can be used by
* UpdateTraceEventDuration to update the duration of COMPLETE events.
*/
virtual uint64_t AddTraceEvent(
char phase, const uint8_t* category_enabled_flag, const char* name,
const char* scope, uint64_t id, uint64_t bind_id, int32_t num_args,
const char** arg_names, const uint8_t* arg_types,
const uint64_t* arg_values,
std::unique_ptr<ConvertableToTraceFormat>* arg_convertables,
unsigned int flags) {
return 0;
}
/**
* Sets the duration field of a COMPLETE trace event. It must be called with
* the handle returned from AddTraceEvent().
**/
virtual void UpdateTraceEventDuration(const uint8_t* category_enabled_flag,
const char* name, uint64_t handle) {}
class TraceStateObserver {
public:
virtual ~TraceStateObserver() = default;
virtual void OnTraceEnabled() = 0;
virtual void OnTraceDisabled() = 0;
};
/** Adds tracing state change observer. */
virtual void AddTraceStateObserver(TraceStateObserver*) {}
/** Removes tracing state change observer. */
virtual void RemoveTraceStateObserver(TraceStateObserver*) {}
};
/**
* V8 Platform abstraction layer.
*
* The embedder has to provide an implementation of this interface before
* initializing the rest of V8.
*/
class Platform {
public:
/**
* This enum is used to indicate whether a task is potentially long running,
* or causes a long wait. The embedder might want to use this hint to decide
* whether to execute the task on a dedicated thread.
*/
enum ExpectedRuntime {
kShortRunningTask,
kLongRunningTask
};
virtual ~Platform() = default;
/**
* Enables the embedder to respond in cases where V8 can't allocate large
* blocks of memory. V8 retries the failed allocation once after calling this
* method. On success, execution continues; otherwise V8 exits with a fatal
* error.
* Embedder overrides of this function must NOT call back into V8.
*/
virtual void OnCriticalMemoryPressure() {}
/**
* Gets the number of threads that are used to execute background tasks. Is
* used to estimate the number of tasks a work package should be split into.
* A return value of 0 means that there are no background threads available.
* Note that a value of 0 won't prohibit V8 from posting tasks using
* |CallOnBackgroundThread|.
*/
virtual size_t NumberOfAvailableBackgroundThreads() { return 0; }
/**
* Returns a TaskRunner which can be used to post a task on the foreground.
* This function should only be called from a foreground thread.
*/
virtual std::unique_ptr<v8::TaskRunner> GetForegroundTaskRunner(
Isolate* isolate) {
// TODO(ahaas): Make this function abstract after it got implemented on all
// platforms.
return {};
}
/**
* Returns a TaskRunner which can be used to post a task on a background.
* This function should only be called from a foreground thread.
*/
virtual std::unique_ptr<v8::TaskRunner> GetBackgroundTaskRunner(
Isolate* isolate) {
// TODO(ahaas): Make this function abstract after it got implemented on all
// platforms.
return {};
}
/**
* Schedules a task to be invoked on a background thread. |expected_runtime|
* indicates that the task will run a long time. The Platform implementation
* takes ownership of |task|. There is no guarantee about order of execution
* of tasks wrt order of scheduling, nor is there a guarantee about the
* thread the task will be run on.
*/
virtual void CallOnBackgroundThread(Task* task,
ExpectedRuntime expected_runtime) = 0;
/**
* Schedules a task to be invoked on a foreground thread wrt a specific
* |isolate|. Tasks posted for the same isolate should be execute in order of
* scheduling. The definition of "foreground" is opaque to V8.
*/
virtual void CallOnForegroundThread(Isolate* isolate, Task* task) = 0;
/**
* Schedules a task to be invoked on a foreground thread wrt a specific
* |isolate| after the given number of seconds |delay_in_seconds|.
* Tasks posted for the same isolate should be execute in order of
* scheduling. The definition of "foreground" is opaque to V8.
*/
virtual void CallDelayedOnForegroundThread(Isolate* isolate, Task* task,
double delay_in_seconds) = 0;
/**
* Schedules a task to be invoked on a foreground thread wrt a specific
* |isolate| when the embedder is idle.
* Requires that SupportsIdleTasks(isolate) is true.
* Idle tasks may be reordered relative to other task types and may be
* starved for an arbitrarily long time if no idle time is available.
* The definition of "foreground" is opaque to V8.
*/
virtual void CallIdleOnForegroundThread(Isolate* isolate, IdleTask* task) {
// TODO(ulan): Make this function abstract after V8 roll in Chromium.
}
/**
* Returns true if idle tasks are enabled for the given |isolate|.
*/
virtual bool IdleTasksEnabled(Isolate* isolate) {
// TODO(ulan): Make this function abstract after V8 roll in Chromium.
return false;
}
/**
* 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;
/**
* Current wall-clock time in milliseconds since epoch.
* This function is expected to return at least millisecond-precision values.
*/
virtual double CurrentClockTimeMillis() = 0;
typedef void (*StackTracePrinter)();
/**
* Returns a function pointer that print a stack trace of the current stack
* on invocation. Disables printing of the stack trace if nullptr.
*/
virtual StackTracePrinter GetStackTracePrinter() { return nullptr; }
/**
* Returns an instance of a v8::TracingController. This must be non-nullptr.
*/
virtual TracingController* GetTracingController() = 0;
protected:
/**
* Default implementation of current wall-clock time in milliseconds
* since epoch. Useful for implementing |CurrentClockTimeMillis| if
* nothing special needed.
*/
static double SystemClockTimeMillis();
};
} // namespace v8
#endif // V8_V8_PLATFORM_H_