// Copyright (c) the JPEG XL 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 LIB_JXL_BASE_DATA_PARALLEL_H_
#define LIB_JXL_BASE_DATA_PARALLEL_H_
// Portable, low-overhead C++11 ThreadPool alternative to OpenMP for
// data-parallel computations.
#include <jxl/parallel_runner.h>
#include <atomic>
#include <cstddef>
#include <cstdint>
#include "lib/jxl/base/compiler_specific.h"
#include "lib/jxl/base/status.h"
#if JXL_COMPILER_MSVC
// suppress warnings about the const & applied to function types
#pragma warning(disable : 4180)
#endif
namespace jxl {
class ThreadPool {
public:
ThreadPool(JxlParallelRunner runner,
void* runner_opaque)
: runner_(runner),
runner_opaque_(runner ? runner_opaque :
static_cast<
void*>(
this)) {}
ThreadPool(
const ThreadPool&) =
delete;
ThreadPool&
operator&(
const ThreadPool&) =
delete;
JxlParallelRunner runner()
const {
return runner_; }
void* runner_opaque()
const {
return runner_opaque_; }
// Runs init_func(num_threads) followed by data_func(task, thread) on worker
// thread(s) for every task in [begin, end). init_func() must return a Status
// indicating whether the initialization succeeded.
// "thread" is an integer smaller than num_threads.
// Not thread-safe - no two calls to Run may overlap.
// Subsequent calls will reuse the same threads.
//
// Precondition: begin <= end.
template <
class InitFunc,
class DataFunc>
Status Run(uint32_t begin, uint32_t end,
const InitFunc& init_func,
const DataFunc& data_func,
const char* caller) {
JXL_ENSURE(begin <= end);
if (begin == end)
return true;
RunCallState<InitFunc, DataFunc> call_state(init_func, data_func);
// The runner_ uses the C convention and returns 0 in case of error, so we
// convert it to a Status.
if (!runner_) {
void* jpegxl_opaque =
static_cast<
void*>(&call_state);
if (call_state.CallInitFunc(jpegxl_opaque, 1) !=
JXL_PARALLEL_RET_SUCCESS) {
return JXL_FAILURE(
"Failed to initialize thread");
}
for (uint32_t i = begin; i < end; i++) {
call_state.CallDataFunc(jpegxl_opaque, i, 0);
}
if (call_state.HasError()) {
return JXL_FAILURE(
"[%s] failed", caller);
}
return true;
}
JxlParallelRetCode ret = (*runner_)(
runner_opaque_,
static_cast<
void*>(&call_state),
&call_state.CallInitFunc, &call_state.CallDataFunc, begin, end);
if (ret != JXL_PARALLEL_RET_SUCCESS || call_state.HasError()) {
return JXL_FAILURE(
"[%s] failed", caller);
}
return true;
}
// Use this as init_func when no initialization is needed.
static Status NoInit(size_t num_threads) {
return true; }
private:
// class holding the state of a Run() call to pass to the runner_ as an
// opaque_jpegxl pointer.
template <
class InitFunc,
class DataFunc>
class RunCallState final {
public:
RunCallState(
const InitFunc& init_func,
const DataFunc& data_func)
: init_func_(init_func), data_func_(data_func) {}
// JxlParallelRunInit interface.
static int CallInitFunc(
void* jpegxl_opaque, size_t num_threads) {
auto* self =
static_cast<RunCallState<InitFunc, DataFunc>*>(jpegxl_opaque);
// Returns -1 when the internal init function returns false Status to
// indicate an error.
if (!self->init_func_(num_threads)) {
self->has_error_ =
true;
return JXL_PARALLEL_RET_RUNNER_ERROR;
}
return JXL_PARALLEL_RET_SUCCESS;
}
// JxlParallelRunFunction interface.
static void CallDataFunc(
void* jpegxl_opaque, uint32_t value,
size_t thread_id) {
auto* self =
static_cast<RunCallState<InitFunc, DataFunc>*>(jpegxl_opaque);
if (self->has_error_)
return;
if (!self->data_func_(value, thread_id)) {
self->has_error_ =
true;
}
}
bool HasError()
const {
return has_error_; }
private:
const InitFunc& init_func_;
const DataFunc& data_func_;
std::atomic<
bool> has_error_{
false};
};
// The caller supplied runner function and its opaque void*.
const JxlParallelRunner runner_;
void*
const runner_opaque_;
};
template <
class InitFunc,
class DataFunc>
Status RunOnPool(ThreadPool* pool,
const uint32_t begin,
const uint32_t end,
const InitFunc& init_func,
const DataFunc& data_func,
const char* caller) {
if (pool == nullptr) {
ThreadPool default_pool(nullptr, nullptr);
return default_pool.Run(begin, end, init_func, data_func, caller);
}
else {
return pool->Run(begin, end, init_func, data_func, caller);
}
}
}
// namespace jxl
#if JXL_COMPILER_MSVC
#pragma warning(
default : 4180)
#endif
#endif // LIB_JXL_BASE_DATA_PARALLEL_H_
