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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 <math.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h> // For abort.
#include <memory>
#include <string>
#include "v8-source-location.h" // NOLINT(build/include_directory)
#include "v8config.h" // NOLINT(build/include_directory)
namespace v8 {
class Isolate;
// Valid priorities supported by the task scheduling infrastructure.
enum class TaskPriority : uint8_t {
/**
* Best effort tasks are not critical for performance of the application. The
* platform implementation should preempt such tasks if higher priority tasks
* arrive.
*/
kBestEffort,
/**
* User visible tasks are long running background tasks that will
* improve performance and memory usage of the application upon completion.
* Example: background compilation and garbage collection.
*/
kUserVisible,
/**
* User blocking tasks are highest priority tasks that block the execution
* thread (e.g. major garbage collection). They must be finished as soon as
* possible.
*/
kUserBlocking,
kMaxPriority = kUserBlocking
};
/**
* 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|.
*
* Embedders should override PostTaskImpl instead of this.
*/
virtual void PostTask(std::unique_ptr<Task> task) {
PostTaskImpl(std::move(task), SourceLocation::Current());
}
/**
* Schedules a task to be invoked by this TaskRunner. The TaskRunner
* implementation takes ownership of |task|. The |task| cannot be nested
* within other task executions.
*
* Tasks which shouldn't be interleaved with JS execution must be posted with
* |PostNonNestableTask| or |PostNonNestableDelayedTask|. This is because the
* embedder may process tasks in a callback which is called during JS
* execution.
*
* In particular, tasks which execute JS must be non-nestable, since JS
* execution is not allowed to nest.
*
* Requires that |TaskRunner::NonNestableTasksEnabled()| is true.
*
* Embedders should override PostNonNestableTaskImpl instead of this.
*/
virtual void PostNonNestableTask(std::unique_ptr<Task> task) {
PostNonNestableTaskImpl(std::move(task), SourceLocation::Current());
}
/**
* 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|.
*
* Embedders should override PostDelayedTaskImpl instead of this.
*/
virtual void PostDelayedTask(std::unique_ptr<Task> task,
double delay_in_seconds) {
PostDelayedTaskImpl(std::move(task), delay_in_seconds,
SourceLocation::Current());
}
/**
* 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|. The |task| cannot be nested
* within other task executions.
*
* Tasks which shouldn't be interleaved with JS execution must be posted with
* |PostNonNestableTask| or |PostNonNestableDelayedTask|. This is because the
* embedder may process tasks in a callback which is called during JS
* execution.
*
* In particular, tasks which execute JS must be non-nestable, since JS
* execution is not allowed to nest.
*
* Requires that |TaskRunner::NonNestableDelayedTasksEnabled()| is true.
*
* Embedders should override PostNonNestableDelayedTaskImpl instead of this.
*/
virtual void PostNonNestableDelayedTask(std::unique_ptr<Task> task,
double delay_in_seconds) {
PostNonNestableDelayedTaskImpl(std::move(task), delay_in_seconds,
SourceLocation::Current());
}
/**
* Schedules an idle task to be invoked by this TaskRunner. The task is
* scheduled when the embedder is idle. Requires that
* |TaskRunner::IdleTasksEnabled()| 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|.
*
* Embedders should override PostIdleTaskImpl instead of this.
*/
virtual void PostIdleTask(std::unique_ptr<IdleTask> task) {
PostIdleTaskImpl(std::move(task), SourceLocation::Current());
}
/**
* Returns true if idle tasks are enabled for this TaskRunner.
*/
virtual bool IdleTasksEnabled() = 0;
/**
* Returns true if non-nestable tasks are enabled for this TaskRunner.
*/
virtual bool NonNestableTasksEnabled() const { return false; }
/**
* Returns true if non-nestable delayed tasks are enabled for this TaskRunner.
*/
virtual bool NonNestableDelayedTasksEnabled() const { return false; }
TaskRunner() = default;
virtual ~TaskRunner() = default;
TaskRunner(const TaskRunner&) = delete;
TaskRunner& operator=(const TaskRunner&) = delete;
protected:
/**
* Implementation of above methods with an additional `location` argument.
*/
virtual void PostTaskImpl(std::unique_ptr<Task> task,
const SourceLocation& location) {}
virtual void PostNonNestableTaskImpl(std::unique_ptr<Task> task,
const SourceLocation& location) {}
virtual void PostDelayedTaskImpl(std::unique_ptr<Task> task,
double delay_in_seconds,
const SourceLocation& location) {}
virtual void PostNonNestableDelayedTaskImpl(std::unique_ptr<Task> task,
double delay_in_seconds,
const SourceLocation& location) {}
virtual void PostIdleTaskImpl(std::unique_ptr<IdleTask> task,
const SourceLocation& location) {}
};
/**
* Delegate that's passed to Job's worker task, providing an entry point to
* communicate with the scheduler.
*/
class JobDelegate {
public:
/**
* Returns true if this thread *must* return from the worker task on the
* current thread ASAP. Workers should periodically invoke ShouldYield (or
* YieldIfNeeded()) as often as is reasonable.
* After this method returned true, ShouldYield must not be called again.
*/
virtual bool ShouldYield() = 0;
/**
* Notifies the scheduler that max concurrency was increased, and the number
* of worker should be adjusted accordingly. See Platform::PostJob() for more
* details.
*/
virtual void NotifyConcurrencyIncrease() = 0;
/**
* Returns a task_id unique among threads currently running this job, such
* that GetTaskId() < worker count. To achieve this, the same task_id may be
* reused by a different thread after a worker_task returns.
*/
virtual uint8_t GetTaskId() = 0;
/**
* Returns true if the current task is called from the thread currently
* running JobHandle::Join().
*/
virtual bool IsJoiningThread() const = 0;
};
/**
* Handle returned when posting a Job. Provides methods to control execution of
* the posted Job.
*/
class JobHandle {
public:
virtual ~JobHandle() = default;
/**
* Notifies the scheduler that max concurrency was increased, and the number
* of worker should be adjusted accordingly. See Platform::PostJob() for more
* details.
*/
virtual void NotifyConcurrencyIncrease() = 0;
/**
* Contributes to the job on this thread. Doesn't return until all tasks have
* completed and max concurrency becomes 0. When Join() is called and max
* concurrency reaches 0, it should not increase again. This also promotes
* this Job's priority to be at least as high as the calling thread's
* priority.
*/
virtual void Join() = 0;
/**
* Forces all existing workers to yield ASAP. Waits until they have all
* returned from the Job's callback before returning.
*/
virtual void Cancel() = 0;
/*
* Forces all existing workers to yield ASAP but doesn’t wait for them.
* Warning, this is dangerous if the Job's callback is bound to or has access
* to state which may be deleted after this call.
*/
virtual void CancelAndDetach() = 0;
/**
* Returns true if there's any work pending or any worker running.
*/
virtual bool IsActive() = 0;
/**
* Returns true if associated with a Job and other methods may be called.
* Returns false after Join() or Cancel() was called. This may return true
* even if no workers are running and IsCompleted() returns true
*/
virtual bool IsValid() = 0;
/**
* Returns true if job priority can be changed.
*/
virtual bool UpdatePriorityEnabled() const { return false; }
/**
* Update this Job's priority.
*/
virtual void UpdatePriority(TaskPriority new_priority) {}
};
/**
* A JobTask represents work to run in parallel from Platform::PostJob().
*/
class JobTask {
public:
virtual ~JobTask() = default;
virtual void Run(JobDelegate* delegate) = 0;
/**
* Controls the maximum number of threads calling Run() concurrently, given
* the number of threads currently assigned to this job and executing Run().
* Run() is only invoked if the number of threads previously running Run() was
* less than the value returned. In general, this should return the latest
* number of incomplete work items (smallest unit of work) left to process,
* including items that are currently in progress. |worker_count| is the
* number of threads currently assigned to this job which some callers may
* need to determine their return value. Since GetMaxConcurrency() is a leaf
* function, it must not call back any JobHandle methods.
*/
virtual size_t GetMaxConcurrency(size_t worker_count) const = 0;
};
/**
* A "blocking call" refers to any call that causes the calling thread to wait
* off-CPU. It includes but is not limited to calls that wait on synchronous
* file I/O operations: read or write a file from disk, interact with a pipe or
* a socket, rename or delete a file, enumerate files in a directory, etc.
* Acquiring a low contention lock is not considered a blocking call.
*/
/**
* BlockingType indicates the likelihood that a blocking call will actually
* block.
*/
enum class BlockingType {
// The call might block (e.g. file I/O that might hit in memory cache).
kMayBlock,
// The call will definitely block (e.g. cache already checked and now pinging
// server synchronously).
kWillBlock
};
/**
* This class is instantiated with CreateBlockingScope() in every scope where a
* blocking call is made and serves as a precise annotation of the scope that
* may/will block. May be implemented by an embedder to adjust the thread count.
* CPU usage should be minimal within that scope. ScopedBlockingCalls can be
* nested.
*/
class ScopedBlockingCall {
public:
virtual ~ScopedBlockingCall() = default;
};
/**
* 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.
*
* Will become obsolete in Perfetto SDK build (v8_use_perfetto = true).
*/
class TracingController {
public:
virtual ~TracingController() = default;
// In Perfetto mode, trace events are written using Perfetto's Track Event
// API directly without going through the embedder. However, it is still
// possible to observe tracing being enabled and disabled.
#if !defined(V8_USE_PERFETTO)
/**
* 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) {}
#endif // !defined(V8_USE_PERFETTO)
class TraceStateObserver {
public:
virtual ~TraceStateObserver() = default;
virtual void OnTraceEnabled() = 0;
virtual void OnTraceDisabled() = 0;
};
/**
* Adds tracing state change observer.
* Does nothing in Perfetto SDK build (v8_use_perfetto = true).
*/
virtual void AddTraceStateObserver(TraceStateObserver*) {}
/**
* Removes tracing state change observer.
* Does nothing in Perfetto SDK build (v8_use_perfetto = true).
*/
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,
kRead,
kReadWrite,
kReadWriteExecute,
kReadExecute,
// Set this when reserving memory that will later require kReadWriteExecute
// permissions. The resulting behavior is platform-specific, currently
// this is used to set the MAP_JIT flag on Apple Silicon.
// TODO(jkummerow): Remove this when Wasm has a platform-independent
// w^x implementation.
// TODO(saelo): Remove this once all JIT pages are allocated through the
// VirtualAddressSpace API.
kNoAccessWillJitLater
};
/**
* 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;
/**
* Recommits discarded pages in the given range with given permissions.
* Discarded pages must be recommitted with their original permissions
* before they are used again.
*/
virtual bool RecommitPages(void* address, size_t length,
Permission permissions) {
// TODO(v8:12797): make it pure once it's implemented on Chromium side.
return false;
}
/**
* Frees memory in the given [address, address + size) range. address and size
* should be operating system page-aligned. The next write to this
* memory area brings the memory transparently back. This should be treated as
* a hint to the OS that the pages are no longer needed. It does not guarantee
* that the pages will be discarded immediately or at all.
*/
virtual bool DiscardSystemPages(void* address, size_t size) { return true; }
/**
* Decommits any wired memory pages in the given range, allowing the OS to
* reclaim them, and marks the region as inacessible (kNoAccess). The address
* range stays reserved and can be accessed again later by changing its
* permissions. However, in that case the memory content is guaranteed to be
* zero-initialized again. The memory must have been previously allocated by a
* call to AllocatePages. Returns true on success, false otherwise.
*/
virtual bool DecommitPages(void* address, size_t size) = 0;
/**
* INTERNAL ONLY: This interface has not been stabilised and may change
* without notice from one release to another without being deprecated first.
*/
class SharedMemoryMapping {
public:
// Implementations are expected to free the shared memory mapping in the
// destructor.
virtual ~SharedMemoryMapping() = default;
virtual void* GetMemory() const = 0;
};
/**
* INTERNAL ONLY: This interface has not been stabilised and may change
* without notice from one release to another without being deprecated first.
*/
class SharedMemory {
public:
// Implementations are expected to free the shared memory in the destructor.
virtual ~SharedMemory() = default;
virtual std::unique_ptr<SharedMemoryMapping> RemapTo(
void* new_address) const = 0;
virtual void* GetMemory() const = 0;
virtual size_t GetSize() const = 0;
};
/**
* INTERNAL ONLY: This interface has not been stabilised and may change
* without notice from one release to another without being deprecated first.
*
* Reserve pages at a fixed address returning whether the reservation is
* possible. The reserved memory is detached from the PageAllocator and so
* should not be freed by it. It's intended for use with
* SharedMemory::RemapTo, where ~SharedMemoryMapping would free the memory.
*/
virtual bool ReserveForSharedMemoryMapping(void* address, size_t size) {
return false;
}
/**
* INTERNAL ONLY: This interface has not been stabilised and may change
* without notice from one release to another without being deprecated first.
*
* Allocates shared memory pages. Not all PageAllocators need support this and
* so this method need not be overridden.
* Allocates a new read-only shared memory region of size |length| and copies
* the memory at |original_address| into it.
*/
virtual std::unique_ptr<SharedMemory> AllocateSharedPages(
size_t length, const void* original_address) {
return {};
}
/**
* INTERNAL ONLY: This interface has not been stabilised and may change
* without notice from one release to another without being deprecated first.
*
* If not overridden and changed to return true, V8 will not attempt to call
* AllocateSharedPages or RemapSharedPages. If overridden, AllocateSharedPages
* and RemapSharedPages must also be overridden.
*/
virtual bool CanAllocateSharedPages() { return false; }
};
/**
* An allocator that uses per-thread permissions to protect the memory.
*
* The implementation is platform/hardware specific, e.g. using pkeys on x64.
*
* INTERNAL ONLY: This interface has not been stabilised and may change
* without notice from one release to another without being deprecated first.
*/
class ThreadIsolatedAllocator {
public:
virtual ~ThreadIsolatedAllocator() = default;
virtual void* Allocate(size_t size) = 0;
virtual void Free(void* object) = 0;
enum class Type {
kPkey,
};
virtual Type Type() const = 0;
/**
* Return the pkey used to implement the thread isolation if Type == kPkey.
*/
virtual int Pkey() const { return -1; }
/**
* Per-thread permissions can be reset on signal handler entry. Even reading
* ThreadIsolated memory will segfault in that case.
* Call this function on signal handler entry to ensure that read permissions
* are restored.
*/
static void SetDefaultPermissionsForSignalHandler();
};
// Opaque type representing a handle to a shared memory region.
using PlatformSharedMemoryHandle = intptr_t;
static constexpr PlatformSharedMemoryHandle kInvalidSharedMemoryHandle = -1;
// Conversion routines from the platform-dependent shared memory identifiers
// into the opaque PlatformSharedMemoryHandle type. These use the underlying
// types (e.g. unsigned int) instead of the typedef'd ones (e.g. mach_port_t)
// to avoid pulling in large OS header files into this header file. Instead,
// the users of these routines are expected to include the respecitve OS
// headers in addition to this one.
#if V8_OS_DARWIN
// Convert between a shared memory handle and a mach_port_t referencing a memory
// entry object.
inline PlatformSharedMemoryHandle SharedMemoryHandleFromMachMemoryEntry(
unsigned int port) {
return static_cast<PlatformSharedMemoryHandle>(port);
}
inline unsigned int MachMemoryEntryFromSharedMemoryHandle(
PlatformSharedMemoryHandle handle) {
return static_cast<unsigned int>(handle);
}
#elif V8_OS_FUCHSIA
// Convert between a shared memory handle and a zx_handle_t to a VMO.
inline PlatformSharedMemoryHandle SharedMemoryHandleFromVMO(uint32_t handle) {
return static_cast<PlatformSharedMemoryHandle>(handle);
}
inline uint32_t VMOFromSharedMemoryHandle(PlatformSharedMemoryHandle handle) {
return static_cast<uint32_t>(handle);
}
#elif V8_OS_WIN
// Convert between a shared memory handle and a Windows HANDLE to a file mapping
// object.
inline PlatformSharedMemoryHandle SharedMemoryHandleFromFileMapping(
void* handle) {
return reinterpret_cast<PlatformSharedMemoryHandle>(handle);
}
inline void* FileMappingFromSharedMemoryHandle(
PlatformSharedMemoryHandle handle) {
return reinterpret_cast<void*>(handle);
}
#else
// Convert between a shared memory handle and a file descriptor.
inline PlatformSharedMemoryHandle SharedMemoryHandleFromFileDescriptor(int fd) {
return static_cast<PlatformSharedMemoryHandle>(fd);
}
inline int FileDescriptorFromSharedMemoryHandle(
PlatformSharedMemoryHandle handle) {
return static_cast<int>(handle);
}
#endif
/**
* Possible permissions for memory pages.
*/
enum class PagePermissions {
kNoAccess,
kRead,
kReadWrite,
kReadWriteExecute,
kReadExecute,
};
/**
* Class to manage a virtual memory address space.
*
* This class represents a contiguous region of virtual address space in which
* sub-spaces and (private or shared) memory pages can be allocated, freed, and
* modified. This interface is meant to eventually replace the PageAllocator
* interface, and can be used as an alternative in the meantime.
*
* This API is not yet stable and may change without notice!
*/
class VirtualAddressSpace {
public:
using Address = uintptr_t;
VirtualAddressSpace(size_t page_size, size_t allocation_granularity,
Address base, size_t size,
PagePermissions max_page_permissions)
: page_size_(page_size),
allocation_granularity_(allocation_granularity),
base_(base),
size_(size),
max_page_permissions_(max_page_permissions) {}
virtual ~VirtualAddressSpace() = default;
/**
* The page size used inside this space. Guaranteed to be a power of two.
* Used as granularity for all page-related operations except for allocation,
* which use the allocation_granularity(), see below.
*
* \returns the page size in bytes.
*/
size_t page_size() const { return page_size_; }
/**
* The granularity of page allocations and, by extension, of subspace
* allocations. This is guaranteed to be a power of two and a multiple of the
* page_size(). In practice, this is equal to the page size on most OSes, but
* on Windows it is usually 64KB, while the page size is 4KB.
*
* \returns the allocation granularity in bytes.
*/
size_t allocation_granularity() const { return allocation_granularity_; }
/**
* The base address of the address space managed by this instance.
*
* \returns the base address of this address space.
*/
Address base() const { return base_; }
/**
* The size of the address space managed by this instance.
*
* \returns the size of this address space in bytes.
*/
size_t size() const { return size_; }
/**
* The maximum page permissions that pages allocated inside this space can
* obtain.
*
* \returns the maximum page permissions.
*/
PagePermissions max_page_permissions() const { return max_page_permissions_; }
/**
* Whether the |address| is inside the address space managed by this instance.
*
* \returns true if it is inside the address space, false if not.
*/
bool Contains(Address address) const {
return (address >= base()) && (address < base() + size());
}
/**
* Sets the random seed so that GetRandomPageAddress() will generate
* repeatable sequences of random addresses.
*
* \param The seed for the PRNG.
*/
virtual void SetRandomSeed(int64_t seed) = 0;
/**
* Returns a random address inside this address space, suitable for page
* allocations hints.
*
* \returns a random address aligned to allocation_granularity().
*/
virtual Address RandomPageAddress() = 0;
/**
* Allocates private memory pages with the given alignment and permissions.
*
* \param hint If nonzero, the allocation is attempted to be placed at the
* given address first. If that fails, the allocation is attempted to be
* placed elsewhere, possibly nearby, but that is not guaranteed. Specifying
* zero for the hint always causes this function to choose a random address.
* The hint, if specified, must be aligned to the specified alignment.
*
* \param size The size of the allocation in bytes. Must be a multiple of the
* allocation_granularity().
*
* \param alignment The alignment of the allocation in bytes. Must be a
* multiple of the allocation_granularity() and should be a power of two.
*
* \param permissions The page permissions of the newly allocated pages.
*
* \returns the start address of the allocated pages on success, zero on
* failure.
*/
static constexpr Address kNoHint = 0;
virtual V8_WARN_UNUSED_RESULT Address
AllocatePages(Address hint, size_t size, size_t alignment,
PagePermissions permissions) = 0;
/**
* Frees previously allocated pages.
*
* This function will terminate the process on failure as this implies a bug
* in the client. As such, there is no return value.
*
* \param address The start address of the pages to free. This address must
* have been obtained through a call to AllocatePages.
*
* \param size The size in bytes of the region to free. This must match the
* size passed to AllocatePages when the pages were allocated.
*/
virtual void FreePages(Address address, size_t size) = 0;
/**
* Sets permissions of all allocated pages in the given range.
*
* This operation can fail due to OOM, in which case false is returned. If
* the operation fails for a reason other than OOM, this function will
* terminate the process as this implies a bug in the client.
*
* \param address The start address of the range. Must be aligned to
* page_size().
*
* \param size The size in bytes of the range. Must be a multiple
* of page_size().
*
* \param permissions The new permissions for the range.
*
* \returns true on success, false on OOM.
*/
virtual V8_WARN_UNUSED_RESULT bool SetPagePermissions(
Address address, size_t size, PagePermissions permissions) = 0;
/**
* Creates a guard region at the specified address.
*
* Guard regions are guaranteed to cause a fault when accessed and generally
* do not count towards any memory consumption limits. Further, allocating
* guard regions can usually not fail in subspaces if the region does not
* overlap with another region, subspace, or page allocation.
*
* \param address The start address of the guard region. Must be aligned to
* the allocation_granularity().
*
* \param size The size of the guard region in bytes. Must be a multiple of
* the allocation_granularity().
*
* \returns true on success, false otherwise.
*/
virtual V8_WARN_UNUSED_RESULT bool AllocateGuardRegion(Address address,
size_t size) = 0;
/**
* Frees an existing guard region.
*
* This function will terminate the process on failure as this implies a bug
* in the client. As such, there is no return value.
*
* \param address The start address of the guard region to free. This address
* must have previously been used as address parameter in a successful
* invocation of AllocateGuardRegion.
*
* \param size The size in bytes of the guard region to free. This must match
* the size passed to AllocateGuardRegion when the region was created.
*/
virtual void FreeGuardRegion(Address address, size_t size) = 0;
/**
* Allocates shared memory pages with the given permissions.
*
* \param hint Placement hint. See AllocatePages.
*
* \param size The size of the allocation in bytes. Must be a multiple of the
* allocation_granularity().
*
* \param permissions The page permissions of the newly allocated pages.
*
* \param handle A platform-specific handle to a shared memory object. See
* the SharedMemoryHandleFromX routines above for ways to obtain these.
*
* \param offset The offset in the shared memory object at which the mapping
* should start. Must be a multiple of the allocation_granularity().
*
* \returns the start address of the allocated pages on success, zero on
* failure.
*/
virtual V8_WARN_UNUSED_RESULT Address
AllocateSharedPages(Address hint, size_t size, PagePermissions permissions,
PlatformSharedMemoryHandle handle, uint64_t offset) = 0;
/**
* Frees previously allocated shared pages.
*
* This function will terminate the process on failure as this implies a bug
* in the client. As such, there is no return value.
*
* \param address The start address of the pages to free. This address must
* have been obtained through a call to AllocateSharedPages.
*
* \param size The size in bytes of the region to free. This must match the
* size passed to AllocateSharedPages when the pages were allocated.
*/
virtual void FreeSharedPages(Address address, size_t size) = 0;
/**
* Whether this instance can allocate subspaces or not.
*
* \returns true if subspaces can be allocated, false if not.
*/
virtual bool CanAllocateSubspaces() = 0;
/*
* Allocate a subspace.
*
* The address space of a subspace stays reserved in the parent space for the
* lifetime of the subspace. As such, it is guaranteed that page allocations
* on the parent space cannot end up inside a subspace.
*
* \param hint Hints where the subspace should be allocated. See
* AllocatePages() for more details.
*
* \param size The size in bytes of the subspace. Must be a multiple of the
* allocation_granularity().
*
* \param alignment The alignment of the subspace in bytes. Must be a multiple
* of the allocation_granularity() and should be a power of two.
*
* \param max_page_permissions The maximum permissions that pages allocated in
* the subspace can obtain.
*
* \returns a new subspace or nullptr on failure.
*/
virtual std::unique_ptr<VirtualAddressSpace> AllocateSubspace(
Address hint, size_t size, size_t alignment,
PagePermissions max_page_permissions) = 0;
//
// TODO(v8) maybe refactor the methods below before stabilizing the API. For
// example by combining them into some form of page operation method that
// takes a command enum as parameter.
//
/**
* Recommits discarded pages in the given range with given permissions.
* Discarded pages must be recommitted with their original permissions
* before they are used again.
*
* \param address The start address of the range. Must be aligned to
* page_size().
*
* \param size The size in bytes of the range. Must be a multiple
* of page_size().
*
* \param permissions The permissions for the range that the pages must have.
*
* \returns true on success, false otherwise.
*/
virtual V8_WARN_UNUSED_RESULT bool RecommitPages(
Address address, size_t size, PagePermissions permissions) = 0;
/**
* Frees memory in the given [address, address + size) range. address and
* size should be aligned to the page_size(). The next write to this memory
* area brings the memory transparently back. This should be treated as a
* hint to the OS that the pages are no longer needed. It does not guarantee
* that the pages will be discarded immediately or at all.
*
* \returns true on success, false otherwise. Since this method is only a
* hint, a successful invocation does not imply that pages have been removed.
*/
virtual V8_WARN_UNUSED_RESULT bool DiscardSystemPages(Address address,
size_t size) {
return true;
}
/**
* Decommits any wired memory pages in the given range, allowing the OS to
* reclaim them, and marks the region as inacessible (kNoAccess). The address
* range stays reserved and can be accessed again later by changing its
* permissions. However, in that case the memory content is guaranteed to be
* zero-initialized again. The memory must have been previously allocated by a
* call to AllocatePages.
*
* \returns true on success, false otherwise.
*/
virtual V8_WARN_UNUSED_RESULT bool DecommitPages(Address address,
size_t size) = 0;
private:
const size_t page_size_;
const size_t allocation_granularity_;
const Address base_;
const size_t size_;
const PagePermissions max_page_permissions_;
};
/**
* V8 Allocator used for allocating zone backings.
*/
class ZoneBackingAllocator {
public:
using MallocFn = void* (*)(size_t);
using FreeFn = void (*)(void*);
virtual MallocFn GetMallocFn() const { return ::malloc; }
virtual FreeFn GetFreeFn() const { return ::free; }
};
/**
* Observer used by V8 to notify the embedder about entering/leaving sections
* with high throughput of malloc/free operations.
*/
class HighAllocationThroughputObserver {
public:
virtual void EnterSection() {}
virtual void LeaveSection() {}
};
/**
* V8 Platform abstraction layer.
*
* The embedder has to provide an implementation of this interface before
* initializing the rest of V8.
*/
class Platform {
public:
virtual ~Platform() = default;
/**
* Allows the embedder to manage memory page allocations.
* Returning nullptr will cause V8 to use the default page allocator.
*/
virtual PageAllocator* GetPageAllocator() = 0;
/**
* Allows the embedder to provide an allocator that uses per-thread memory
* permissions to protect allocations.
* Returning nullptr will cause V8 to disable protections that rely on this
* feature.
*/
virtual ThreadIsolatedAllocator* GetThreadIsolatedAllocator() {
return nullptr;
}
/**
* Allows the embedder to specify a custom allocator used for zones.
*/
virtual ZoneBackingAllocator* GetZoneBackingAllocator() {
static ZoneBackingAllocator default_allocator;
return &default_allocator;
}
/**
* 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 max number of worker threads that may be used to execute
* concurrent work scheduled for any single TaskPriority by
* Call(BlockingTask)OnWorkerThread() or PostJob(). 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() = 0;
/**
* Returns a TaskRunner which can be used to post a task on the foreground.
* The TaskRunner's NonNestableTasksEnabled() must be true. This function
* should only be called from a foreground thread.
* TODO(chromium:1448758): Deprecate once |GetForegroundTaskRunner(Isolate*,
* TaskPriority)| is ready.
*/
virtual std::shared_ptr<v8::TaskRunner> GetForegroundTaskRunner(
Isolate* isolate) {
return GetForegroundTaskRunner(isolate, TaskPriority::kUserBlocking);
}
/**
* Returns a TaskRunner with a specific |priority| which can be used to post a
* task on the foreground thread. The TaskRunner's NonNestableTasksEnabled()
* must be true. This function should only be called from a foreground thread.
* TODO(chromium:1448758): Make pure virtual once embedders implement it.
*/
virtual std::shared_ptr<v8::TaskRunner> GetForegroundTaskRunner(
Isolate* isolate, TaskPriority priority) {
return nullptr;
}
/**
* Schedules a task to be invoked on a worker thread.
* Embedders should override PostTaskOnWorkerThreadImpl() instead of
* CallOnWorkerThread().
*/
void CallOnWorkerThread(
std::unique_ptr<Task> task,
const SourceLocation& location = SourceLocation::Current()) {
PostTaskOnWorkerThreadImpl(TaskPriority::kUserVisible, std::move(task),
location);
}
/**
* Schedules a task that blocks the main thread to be invoked with
* high-priority on a worker thread.
* Embedders should override PostTaskOnWorkerThreadImpl() instead of
* CallBlockingTaskOnWorkerThread().
*/
void CallBlockingTaskOnWorkerThread(
std::unique_ptr<Task> task,
const SourceLocation& location = SourceLocation::Current()) {
// Embedders may optionally override this to process these tasks in a high
// priority pool.
PostTaskOnWorkerThreadImpl(TaskPriority::kUserBlocking, std::move(task),
location);
}
/**
* Schedules a task to be invoked with low-priority on a worker thread.
* Embedders should override PostTaskOnWorkerThreadImpl() instead of
* CallLowPriorityTaskOnWorkerThread().
*/
void CallLowPriorityTaskOnWorkerThread(
std::unique_ptr<Task> task,
const SourceLocation& location = SourceLocation::Current()) {
// Embedders may optionally override this to process these tasks in a low
// priority pool.
PostTaskOnWorkerThreadImpl(TaskPriority::kBestEffort, std::move(task),
location);
}
/**
* Schedules a task to be invoked on a worker thread after |delay_in_seconds|
* expires.
* Embedders should override PostDelayedTaskOnWorkerThreadImpl() instead of
* CallDelayedOnWorkerThread().
*/
void CallDelayedOnWorkerThread(
std::unique_ptr<Task> task, double delay_in_seconds,
const SourceLocation& location = SourceLocation::Current()) {
PostDelayedTaskOnWorkerThreadImpl(TaskPriority::kUserVisible,
std::move(task), delay_in_seconds,
location);
}
/**
* Returns true if idle tasks are enabled for the given |isolate|.
*/
virtual bool IdleTasksEnabled(Isolate* isolate) { return false; }
/**
* 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:
* class MyJobTask : public JobTask {
* public:
* MyJobTask(...) : worker_queue_(...) {}
* // JobTask:
* 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();
*
* 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).
* Embedders should override CreateJobImpl() instead of PostJob().
*/
std::unique_ptr<JobHandle> PostJob(
TaskPriority priority, std::unique_ptr<JobTask> job_task,
const SourceLocation& location = SourceLocation::Current()) {
auto handle = CreateJob(priority, std::move(job_task), location);
handle->NotifyConcurrencyIncrease();
return handle;
}
/**
* Creates and returns a JobHandle associated with a Job. Unlike PostJob(),
* this doesn't immediately schedules |worker_task| to run; the Job is then
* scheduled by calling either NotifyConcurrencyIncrease() or Join().
*
* A sufficient CreateJob() implementation that uses the default Job provided
* in libplatform looks like:
* std::unique_ptr<JobHandle> CreateJob(
* TaskPriority priority, std::unique_ptr<JobTask> job_task) override {
* return v8::platform::NewDefaultJobHandle(
* this, priority, std::move(job_task), NumberOfWorkerThreads());
* }
*
* Embedders should override CreateJobImpl() instead of CreateJob().
*/
std::unique_ptr<JobHandle> CreateJob(
TaskPriority priority, std::unique_ptr<JobTask> job_task,
const SourceLocation& location = SourceLocation::Current()) {
return CreateJobImpl(priority, std::move(job_task), location);
}
/**
* Instantiates a ScopedBlockingCall to annotate a scope that may/will block.
*/
virtual std::unique_ptr<ScopedBlockingCall> CreateBlockingScope(
BlockingType blocking_type) {
return nullptr;
}
/**
* 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. Use
* CurrentClockTimeMillisHighResolution() when higher precision is
* required.
*/
virtual int64_t CurrentClockTimeMilliseconds() {
return static_cast<int64_t>(floor(CurrentClockTimeMillis()));
}
/**
* This function is deprecated and will be deleted. Use either
* CurrentClockTimeMilliseconds() or
* CurrentClockTimeMillisecondsHighResolution().
*/
virtual double CurrentClockTimeMillis() = 0;
/**
* Same as CurrentClockTimeMilliseconds(), but with more precision.
*/
virtual double CurrentClockTimeMillisecondsHighResolution() {
return CurrentClockTimeMillis();
}
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;
/**
* Tells the embedder to generate and upload a crashdump during an unexpected
* but non-critical scenario.
*/
virtual void DumpWithoutCrashing() {}
/**
* Allows the embedder to observe sections with high throughput allocation
* operations.
*/
virtual HighAllocationThroughputObserver*
GetHighAllocationThroughputObserver() {
static HighAllocationThroughputObserver default_observer;
return &default_observer;
}
protected:
/**
* Default implementation of current wall-clock time in milliseconds
* since epoch. Useful for implementing |CurrentClockTimeMillis| if
* nothing special needed.
*/
V8_EXPORT static double SystemClockTimeMillis();
/**
* Creates and returns a JobHandle associated with a Job.
*/
virtual std::unique_ptr<JobHandle> CreateJobImpl(
TaskPriority priority, std::unique_ptr<JobTask> job_task,
const SourceLocation& location) = 0;
/**
* Schedules a task with |priority| to be invoked on a worker thread.
*/
virtual void PostTaskOnWorkerThreadImpl(TaskPriority priority,
std::unique_ptr<Task> task,
const SourceLocation& location) = 0;
/**
* Schedules a task with |priority| to be invoked on a worker thread after
* |delay_in_seconds| expires.
*/
virtual void PostDelayedTaskOnWorkerThreadImpl(
TaskPriority priority, std::unique_ptr<Task> task,
double delay_in_seconds, const SourceLocation& location) = 0;
};
} // namespace v8
#endif // V8_V8_PLATFORM_H_