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// 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>
#include "v8config.h" // NOLINT(build/include)
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. These function calls are
* 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 these functions on their own; they are 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;
}
virtual uint64_t AddTraceEventWithTimestamp(
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, int64_t timestamp) {
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*) {}
};
/**
* A V8 memory page allocator.
*
* Can be implemented by an embedder to manage large host OS allocations.
*/
class PageAllocator {
public:
virtual ~PageAllocator() = default;
/**
* Gets the page granularity for AllocatePages and FreePages. Addresses and
* lengths for those calls should be multiples of AllocatePageSize().
*/
virtual size_t AllocatePageSize() = 0;
/**
* Gets the page granularity for SetPermissions and ReleasePages. Addresses
* and lengths for those calls should be multiples of CommitPageSize().
*/
virtual size_t CommitPageSize() = 0;
/**
* Sets the random seed so that GetRandomMmapAddr() will generate repeatable
* sequences of random mmap addresses.
*/
virtual void SetRandomMmapSeed(int64_t seed) = 0;
/**
* Returns a randomized address, suitable for memory allocation under ASLR.
* The address will be aligned to AllocatePageSize.
*/
virtual void* GetRandomMmapAddr() = 0;
/**
* Memory permissions.
*/
enum Permission {
kNoAccess,
kReadWrite,
// TODO(hpayer): Remove this flag. Memory should never be rwx.
kReadWriteExecute,
kReadExecute
};
/**
* Allocates memory in range with the given alignment and permission.
*/
virtual void* AllocatePages(void* address, size_t length, size_t alignment,
Permission permissions) = 0;
/**
* Frees memory in a range that was allocated by a call to AllocatePages.
*/
virtual bool FreePages(void* address, size_t length) = 0;
/**
* Releases memory in a range that was allocated by a call to AllocatePages.
*/
virtual bool ReleasePages(void* address, size_t length,
size_t new_length) = 0;
/**
* Sets permissions on pages in an allocated range.
*/
virtual bool SetPermissions(void* address, size_t length,
Permission permissions) = 0;
};
/**
* 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;
/**
* Allows the embedder to manage memory page allocations.
*/
virtual PageAllocator* GetPageAllocator() {
// TODO(bbudge) Make this abstract after all embedders implement this.
return nullptr;
}
/**
* 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() {
// TODO(bbudge) Remove this when embedders override the following method.
// See crbug.com/634547.
}
/**
* Enables the embedder to respond in cases where V8 can't allocate large
* memory regions. The |length| parameter is the amount of memory needed.
* Returns true if memory is now available. Returns false if no memory could
* be made available. V8 will retry allocations until this method returns
* false.
*
* Embedder overrides of this function must NOT call back into V8.
*/
virtual bool OnCriticalMemoryPressure(size_t length) { return false; }
/**
* Gets the number of worker threads used by GetWorkerThreadsTaskRunner() and
* CallOnWorkerThread(). This can be used to estimate the number of tasks a
* work package should be split into. A return value of 0 means that there are
* no worker threads available. Note that a value of 0 won't prohibit V8 from
* posting tasks using |CallOnWorkerThread|.
*/
virtual int NumberOfWorkerThreads() {
return static_cast<int>(NumberOfAvailableBackgroundThreads());
}
/**
* Deprecated. Use NumberOfWorkerThreads() instead.
* TODO(gab): Remove this when all embedders override
* NumberOfWorkerThreads() instead.
*/
V8_DEPRECATE_SOON(
"NumberOfAvailableBackgroundThreads() is deprecated, use "
"NumberOfAvailableBackgroundThreads() instead.",
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::shared_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.
*/
V8_DEPRECATE_SOON(
"GetBackgroundTaskRunner() is deprecated, use "
"GetWorkerThreadsTaskRunner() "
"instead.",
virtual std::shared_ptr<v8::TaskRunner> GetBackgroundTaskRunner(
Isolate* isolate)) {
// TODO(gab): Remove this method when all embedders have moved to
// GetWorkerThreadsTaskRunner().
// An implementation needs to be provided here because this is called by the
// default GetWorkerThreadsTaskRunner() implementation below. In practice
// however, all code either:
// - Overrides GetWorkerThreadsTaskRunner() (thus not making this call) --
// i.e. all v8 code.
// - Overrides this method (thus not making this call) -- i.e. all
// unadapted embedders.
abort();
}
/**
* Returns a TaskRunner which can be used to post async tasks on a worker.
* This function should only be called from a foreground thread.
*/
virtual std::shared_ptr<v8::TaskRunner> GetWorkerThreadsTaskRunner(
Isolate* isolate) {
// TODO(gab): Make this function abstract after it got implemented on all
// platforms.
return GetBackgroundTaskRunner(isolate);
}
/**
* 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.
*/
V8_DEPRECATE_SOON(
"ExpectedRuntime is deprecated, use CallOnWorkerThread(Task*) "
"instead.",
virtual void CallOnBackgroundThread(Task* task,
ExpectedRuntime expected_runtime)) {
// An implementation needs to be provided here because this is called by the
// default implementation below. In practice however, all code either:
// - Overrides the new method (thus not making this call) -- i.e. all v8
// code.
// - Overrides this method (thus not making this call) -- i.e. all
// unadapted embedders.
abort();
}
/**
* Schedules a task to be invoked on a worker thread.
* TODO(gab): Make pure virtual when all embedders override this instead of
* CallOnBackgroundThread().
*/
virtual void CallOnWorkerThread(Task* task) {
CallOnBackgroundThread(task, kShortRunningTask);
}
/**
* Schedules a task that blocks the main thread to be invoked with
* high-priority on a worker thread.
*/
virtual void CallBlockingTaskOnWorkerThread(Task* task) {
// TODO(gab): Make pure-virtual when all embedders override this.
CallOnWorkerThread(task);
}
/**
* 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_