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1098 lines (866 loc) · 27.1 KB
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#pragma once
#include "../taskflow.hpp"
/**
@file pipeline.hpp
@brief pipeline include file
*/
namespace tf {
// ----------------------------------------------------------------------------
// Class Definition: Pipeflow
// ----------------------------------------------------------------------------
/**
@class Pipeflow
@brief class to create a pipeflow object used by the pipe callable
Pipeflow represents a <i>scheduling token</i> in the pipeline scheduling
framework. A pipeflow is created by the pipeline scheduler at runtime to
pass to the pipe callable. Users can query the present statistics
of that scheduling token, including the line identifier, pipe identifier,
and token identifier, and build their application algorithms based on
these statistics.
At the first stage, users can explicitly call the stop method
to stop the pipeline scheduler.
@code{.cpp}
tf::Pipe{tf::PipeType::SERIAL, [](tf::Pipeflow& pf){
std::cout << "token id=" << pf.token()
<< " at line=" << pf.line()
<< " at pipe=" << pf.pipe()
<< '\n';
}};
@endcode
Pipeflow can only be created privately by the tf::Pipeline and
be used through the pipe callable.
*/
class Pipeflow {
template <typename... Ps>
friend class Pipeline;
template <typename P>
friend class ScalablePipeline;
public:
/**
@brief default constructor
*/
Pipeflow() = default;
/**
@brief queries the line identifier of the present token
*/
size_t line() const {
return _line;
}
/**
@brief queries the pipe identifier of the present token
*/
size_t pipe() const {
return _pipe;
}
/**
@brief queries the token identifier
*/
size_t token() const {
return _token;
}
/**
@brief stops the pipeline scheduling
Only the first pipe can call this method to stop the pipeline.
Others have no effect.
*/
void stop() {
_stop = true;
}
private:
size_t _line;
size_t _pipe;
size_t _token;
bool _stop;
};
// ----------------------------------------------------------------------------
// Class Definition: PipeType
// ----------------------------------------------------------------------------
/**
@enum PipeType
@brief enumeration of all pipe types
*/
enum class PipeType : int {
/** @brief parallel type */
PARALLEL = 1,
/** @brief serial type */
SERIAL = 2
};
// ----------------------------------------------------------------------------
// Class Definition: Pipe
// ----------------------------------------------------------------------------
/**
@class Pipe
@brief class to create a pipe object for a pipeline stage
@tparam C callable type
A pipe represents a stage of a pipeline. A pipe can be either
@em parallel direction or @em serial direction (specified by tf::PipeType)
and is coupled with a callable to invoke by the pipeline scheduler.
The callable must take a tf::Pipeflow object in reference:
@code{.cpp}
Pipe{PipeType::SERIAL, [](tf::Pipeflow&){}}
@endcode
The pipeflow object is used to query the statistics of a scheduling token
in the pipeline, such as pipe, line, and token numbers.
*/
template <typename C>
class Pipe {
template <typename... Ps>
friend class Pipeline;
template <typename P>
friend class ScalablePipeline;
public:
/**
@brief alias of the callable type
*/
using callable_t = C;
/**
@brief default constructor
*/
Pipe() = default;
/**
@brief constructs the pipe object
@param d pipe type (tf::PipeType)
@param callable callable type
The constructor constructs a pipe with the given direction
(either tf::PipeType::SERIAL or tf::PipeType::PARALLEL) and the
given callable. The callable must take a tf::Pipeflow object in reference:
@code{.cpp}
Pipe{PipeType::SERIAL, [](tf::Pipeflow&){}}
@endcode
When creating a pipeline, the direction of the first pipe must be serial
(tf::PipeType::SERIAL).
*/
Pipe(PipeType d, C&& callable) :
_type{d}, _callable{std::forward<C>(callable)} {
}
/**
@brief queries the type of the pipe
Returns the type of the callable.
*/
PipeType type() const {
return _type;
}
/**
@brief assigns a new type to the pipe
@param type a tf::PipeType variable
*/
void type(PipeType type) {
_type = type;
}
/**
@brief assigns a new callable to the pipe
@tparam U callable type
@param callable a callable object constructible from std::function<void(tf::Pipeflow&)>
Assigns a new callable to the pipe with universal forwarding.
*/
template <typename U>
void callable(U&& callable) {
_callable = std::forward<U>(callable);
}
private:
PipeType _type;
C _callable;
};
// ----------------------------------------------------------------------------
// Class Definition: Pipeline
// ----------------------------------------------------------------------------
/**
@class Pipeline
@brief class to create a pipeline scheduling framework
@tparam Ps pipe types
A pipeline is a composable graph object for users to create a
<i>pipeline scheduling framework</i> using a module task in a taskflow.
Unlike the conventional pipeline programming frameworks (e.g., Intel TBB),
%Taskflow's pipeline algorithm does not provide any data abstraction,
which often restricts users from optimizing data layouts in their applications,
but a flexible framework for users to customize their application data
atop our pipeline scheduling.
The following code creates a pipeline of four parallel lines to schedule
tokens through three serial pipes:
@code{.cpp}
tf::Taskflow taskflow;
tf::Executor executor;
const size_t num_lines = 4;
const size_t num_pipes = 3;
// create a custom data buffer
std::array<std::array<int, num_pipes>, num_lines> buffer;
// create a pipeline graph of four concurrent lines and three serial pipes
tf::Pipeline pipeline(num_lines,
// first pipe must define a serial direction
tf::Pipe{tf::PipeType::SERIAL, [&buffer](tf::Pipeflow& pf) {
// generate only 5 scheduling tokens
if(pf.token() == 5) {
pf.stop();
}
// save the token id into the buffer
else {
buffer[pf.line()][pf.pipe()] = pf.token();
}
}},
tf::Pipe{tf::PipeType::SERIAL, [&buffer] (tf::Pipeflow& pf) {
// propagate the previous result to this pipe by adding one
buffer[pf.line()][pf.pipe()] = buffer[pf.line()][pf.pipe()-1] + 1;
}},
tf::Pipe{tf::PipeType::SERIAL, [&buffer](tf::Pipeflow& pf){
// propagate the previous result to this pipe by adding one
buffer[pf.line()][pf.pipe()] = buffer[pf.line()][pf.pipe()-1] + 1;
}}
);
// build the pipeline graph using composition
tf::Task init = taskflow.emplace([](){ std::cout << "ready\n"; })
.name("starting pipeline");
tf::Task task = taskflow.composed_of(pipeline)
.name("pipeline");
tf::Task stop = taskflow.emplace([](){ std::cout << "stopped\n"; })
.name("pipeline stopped");
// create task dependency
init.precede(task);
task.precede(stop);
// run the pipeline
executor.run(taskflow).wait();
@endcode
The above example creates a pipeline graph that schedules five tokens over
four parallel lines in a circular fashion, as depicted below:
@code{.shell-session}
o -> o -> o
| | |
v v v
o -> o -> o
| | |
v v v
o -> o -> o
| | |
v v v
o -> o -> o
@endcode
At each pipe stage, the program propagates the result to the next pipe
by adding one to the result stored in a custom data storage, @c buffer.
The pipeline scheduler will generate five scheduling tokens and then stop.
Internally, tf::Pipeline uses std::tuple to store the given sequence of pipes.
The definition of each pipe can be different, completely decided by the compiler
to optimize the object layout.
After a pipeline is constructed, it is not possible to change its pipes.
If applications need to change these pipes, please use tf::ScalablePipeline.
*/
template <typename... Ps>
class Pipeline {
static_assert(sizeof...(Ps)>0, "must have at least one pipe");
/**
@private
*/
struct Line {
std::atomic<size_t> join_counter;
};
/**
@private
*/
struct PipeMeta {
PipeType type;
};
public:
/**
@brief constructs a pipeline object
@param num_lines the number of parallel lines
@param ps a list of pipes
Constructs a pipeline of up to @c num_lines parallel lines to schedule
tokens through the given linear chain of pipes.
The first pipe must define a serial direction (tf::PipeType::SERIAL)
or an exception will be thrown.
*/
Pipeline(size_t num_lines, Ps&&... ps);
/**
@brief constructs a pipeline object
@param num_lines the number of parallel lines
@param ps a tuple of pipes
Constructs a pipeline of up to @c num_lines parallel lines to schedule
tokens through the given linear chain of pipes.
The first pipe must define a serial direction (tf::PipeType::SERIAL)
or an exception will be thrown.
*/
Pipeline(size_t num_lines, std::tuple<Ps...>&& ps);
/**
@brief queries the number of parallel lines
The function returns the number of parallel lines given by the user
upon the construction of the pipeline.
The number of lines represents the maximum parallelism this pipeline
can achieve.
*/
size_t num_lines() const noexcept;
/**
@brief queries the number of pipes
The Function returns the number of pipes given by the user
upon the construction of the pipeline.
*/
constexpr size_t num_pipes() const noexcept;
/**
@brief resets the pipeline
Resetting the pipeline to the initial state. After resetting a pipeline,
its token identifier will start from zero as if the pipeline was just
constructed.
*/
void reset();
/**
@brief queries the number of generated tokens in the pipeline
The number represents the total scheduling tokens that has been
generated by the pipeline so far.
*/
size_t num_tokens() const noexcept;
/**
@brief obtains the graph object associated with the pipeline construct
This method is primarily used as an opaque data structure for creating
a module task of the this pipeline.
*/
Graph& graph();
private:
Graph _graph;
size_t _num_tokens;
std::tuple<Ps...> _pipes;
std::array<PipeMeta, sizeof...(Ps)> _meta;
std::vector<std::array<Line, sizeof...(Ps)>> _lines;
std::vector<Task> _tasks;
std::vector<Pipeflow> _pipeflows;
template <size_t... I>
auto _gen_meta(std::tuple<Ps...>&&, std::index_sequence<I...>);
void _on_pipe(Pipeflow&, Runtime&);
void _build();
};
// constructor
template <typename... Ps>
Pipeline<Ps...>::Pipeline(size_t num_lines, Ps&&... ps) :
_pipes {std::make_tuple(std::forward<Ps>(ps)...)},
_meta {PipeMeta{ps.type()}...},
_lines (num_lines),
_tasks (num_lines + 1),
_pipeflows (num_lines) {
if(num_lines == 0) {
TF_THROW("must have at least one line");
}
if(std::get<0>(_pipes).type() != PipeType::SERIAL) {
TF_THROW("first pipe must be serial");
}
reset();
_build();
}
// constructor
template <typename... Ps>
Pipeline<Ps...>::Pipeline(size_t num_lines, std::tuple<Ps...>&& ps) :
_pipes {std::forward<std::tuple<Ps...>>(ps)},
_meta {_gen_meta(
std::forward<std::tuple<Ps...>>(ps), std::make_index_sequence<sizeof...(Ps)>{}
)},
_lines (num_lines),
_tasks (num_lines + 1),
_pipeflows (num_lines) {
if(num_lines == 0) {
TF_THROW("must have at least one line");
}
if(std::get<0>(_pipes).type() != PipeType::SERIAL) {
TF_THROW("first pipe must be serial");
}
reset();
_build();
}
// Function: _get_meta
template <typename... Ps>
template <size_t... I>
auto Pipeline<Ps...>::_gen_meta(std::tuple<Ps...>&& ps, std::index_sequence<I...>) {
return std::array{PipeMeta{std::get<I>(ps).type()}...};
}
// Function: num_lines
template <typename... Ps>
size_t Pipeline<Ps...>::num_lines() const noexcept {
return _pipeflows.size();
}
// Function: num_pipes
template <typename... Ps>
constexpr size_t Pipeline<Ps...>::num_pipes() const noexcept {
return sizeof...(Ps);
}
// Function: num_tokens
template <typename... Ps>
size_t Pipeline<Ps...>::num_tokens() const noexcept {
return _num_tokens;
}
// Function: graph
template <typename... Ps>
Graph& Pipeline<Ps...>::graph() {
return _graph;
}
// Function: reset
template <typename... Ps>
void Pipeline<Ps...>::reset() {
_num_tokens = 0;
for(size_t l = 0; l<num_lines(); l++) {
_pipeflows[l]._pipe = 0;
_pipeflows[l]._line = l;
}
_lines[0][0].join_counter.store(0, std::memory_order_relaxed);
for(size_t l=1; l<num_lines(); l++) {
for(size_t f=1; f<num_pipes(); f++) {
_lines[l][f].join_counter.store(
static_cast<size_t>(_meta[f].type), std::memory_order_relaxed
);
}
}
for(size_t f=1; f<num_pipes(); f++) {
_lines[0][f].join_counter.store(1, std::memory_order_relaxed);
}
for(size_t l=1; l<num_lines(); l++) {
_lines[l][0].join_counter.store(
static_cast<size_t>(_meta[0].type) - 1, std::memory_order_relaxed
);
}
}
// Procedure: _on_pipe
template <typename... Ps>
void Pipeline<Ps...>::_on_pipe(Pipeflow& pf, Runtime&) {
visit_tuple([&](auto&& pipe){
pipe._callable(pf);
}, _pipes, pf._pipe);
}
// Procedure: _build
template <typename... Ps>
void Pipeline<Ps...>::_build() {
using namespace std::literals::string_literals;
FlowBuilder fb(_graph);
// init task
_tasks[0] = fb.emplace([this]() {
return static_cast<int>(_num_tokens % num_lines());
}).name("cond");
// line task
for(size_t l = 0; l < num_lines(); l++) {
_tasks[l + 1] = fb.emplace([this, l] (tf::Runtime& rt) mutable {
auto pf = &_pipeflows[l];
pipeline:
_lines[pf->_line][pf->_pipe].join_counter.store(
static_cast<size_t>(_meta[pf->_pipe].type), std::memory_order_relaxed
);
if (pf->_pipe == 0) {
pf->_token = _num_tokens;
if (pf->_stop = false, _on_pipe(*pf, rt); pf->_stop == true) {
// here, the pipeline is not stopped yet because other
// lines of tasks may still be running their last stages
return;
}
++_num_tokens;
}
else {
_on_pipe(*pf, rt);
}
size_t c_f = pf->_pipe;
size_t n_f = (pf->_pipe + 1) % num_pipes();
size_t n_l = (pf->_line + 1) % num_lines();
pf->_pipe = n_f;
// ---- scheduling starts here ----
// Notice that the shared variable f must not be changed after this
// point because it can result in data race due to the following
// condition:
//
// a -> b
// | |
// v v
// c -> d
//
// d will be spawned by either c or b, so if c changes f but b spawns d
// then data race on f will happen
std::array<int, 2> retval;
size_t n = 0;
// downward dependency
if(_meta[c_f].type == PipeType::SERIAL &&
_lines[n_l][c_f].join_counter.fetch_sub(
1, std::memory_order_acq_rel) == 1
) {
retval[n++] = 1;
}
// forward dependency
if(_lines[pf->_line][n_f].join_counter.fetch_sub(
1, std::memory_order_acq_rel) == 1
) {
retval[n++] = 0;
}
// notice that the task index starts from 1
switch(n) {
case 2: {
rt.schedule(_tasks[n_l+1]);
goto pipeline;
}
case 1: {
if (retval[0] == 1) {
pf = &_pipeflows[n_l];
}
goto pipeline;
}
}
}).name("rt-"s + std::to_string(l));
_tasks[0].precede(_tasks[l+1]);
}
}
// ----------------------------------------------------------------------------
// Class Definition: ScalablePipeline
// ----------------------------------------------------------------------------
/**
@class ScalablePipeline
@brief class to create a scalable pipeline object
@tparam P type of the iterator to a range of pipes
A scalable pipeline is a composable graph object for users to create a
<i>pipeline scheduling framework</i> using a module task in a taskflow.
Unlike tf::Pipeline that instantiates all pipes upon the construction time,
tf::ScalablePipeline allows variable assignments of pipes using range iterators.
Users can also reset a scalable pipeline to a different range of pipes
between runs. The following code creates a scalable pipeline of four
parallel lines to schedule tokens through three serial pipes in a custom storage,
then resetting the pipeline to a new range of five serial pipes:
@code{.cpp}
tf::Taskflow taskflow("pipeline");
tf::Executor executor;
const size_t num_lines = 4;
// create data storage
std::array<int, num_lines> buffer;
// define the pipe callable
auto pipe_callable = [&buffer] (tf::Pipeflow& pf) mutable {
switch(pf.pipe()) {
// first stage generates only 5 scheduling tokens and saves the
// token number into the buffer.
case 0: {
if(pf.token() == 5) {
pf.stop();
}
else {
printf("stage 1: input token = %zu\n", pf.token());
buffer[pf.line()] = pf.token();
}
return;
}
break;
// other stages propagate the previous result to this pipe and
// increment it by one
default: {
printf(
"stage %zu: input buffer[%zu] = %d\n", pf.pipe(), pf.line(), buffer[pf.line()]
);
buffer[pf.line()] = buffer[pf.line()] + 1;
}
break;
}
};
// create a vector of three pipes
std::vector< tf::Pipe<std::function<void(tf::Pipeflow&)>> > pipes;
for(size_t i=0; i<3; i++) {
pipes.emplace_back(tf::PipeType::SERIAL, pipe_callable);
}
// create a pipeline of four parallel lines based on the given vector of pipes
tf::ScalablePipeline pl(num_lines, pipes.begin(), pipes.end());
// build the pipeline graph using composition
tf::Task init = taskflow.emplace([](){ std::cout << "ready\n"; })
.name("starting pipeline");
tf::Task task = taskflow.composed_of(pl)
.name("pipeline");
tf::Task stop = taskflow.emplace([](){ std::cout << "stopped\n"; })
.name("pipeline stopped");
// create task dependency
init.precede(task);
task.precede(stop);
// dump the pipeline graph structure (with composition)
taskflow.dump(std::cout);
// run the pipeline
executor.run(taskflow).wait();
// reset the pipeline to a new range of five pipes and starts from
// the initial state (i.e., token counts from zero)
for(size_t i=0; i<2; i++) {
pipes.emplace_back(tf::PipeType::SERIAL, pipe_callable);
}
pl.reset(pipes.begin(), pipes.end());
executor.run(taskflow).wait();
@endcode
The above example creates a pipeline graph that schedules five tokens over
four parallel lines in a circular fashion, first going through three serial pipes
and then five serial pipes:
@code{.shell-session}
# initial construction of three serial pipes
o -> o -> o
| | |
v v v
o -> o -> o
| | |
v v v
o -> o -> o
| | |
v v v
o -> o -> o
# resetting to a new range of five serial pipes
o -> o -> o -> o -> o
| | | | |
v v v v v
o -> o -> o -> o -> o
| | | | |
v v v v v
o -> o -> o -> o -> o
| | | | |
v v v v v
o -> o -> o -> o -> o
@endcode
Each pipe has the same type of `%tf::Pipe<%std::function<void(%tf::Pipeflow&)>>`
and is kept in a vector that is amenable to change.
We construct the scalable pipeline using two range iterators pointing to the
beginning and the end of the vector.
At each pipe stage, the program propagates the result to the next pipe
by adding one to the result stored in a custom data storage, @c buffer.
The pipeline scheduler will generate five scheduling tokens and then stop.
*/
template <typename P>
class ScalablePipeline {
/**
@private
*/
struct Line {
std::atomic<size_t> join_counter;
};
public:
/**
@brief pipe type
*/
using pipe_type = typename std::iterator_traits<P>::value_type;
/**
@brief constructs an empty scalable pipeline object
@param num_lines the number of parallel lines
An empty scalable pipeline does not have any pipes.
The pipeline needs to be reset to a valid range of pipes
before running.
*/
ScalablePipeline(size_t num_lines);
/**
@brief constructs a scalable pipeline object
@param num_lines the number of parallel lines
@param first iterator to the beginning of the range
@param last iterator to the end of the range
Constructs a pipeline from the given range of pipes specified in
<tt>[first, last)</tt> using @c num_lines parallel lines.
The first pipe must define a serial direction (tf::PipeType::SERIAL)
or an exception will be thrown.
*/
ScalablePipeline(size_t num_lines, P first, P last);
/**
@brief queries the number of parallel lines
The function returns the number of parallel lines given by the user
upon the construction of the pipeline.
The number of lines represents the maximum parallelism this pipeline
can achieve.
*/
size_t num_lines() const noexcept;
/**
@brief queries the number of pipes
The Function returns the number of pipes given by the user
upon the construction of the pipeline.
*/
size_t num_pipes() const noexcept;
/**
@brief resets the pipeline
Resets the pipeline to the initial state. After resetting a pipeline,
its token identifier will start from zero.
*/
void reset();
/**
@brief resets the pipeline with a new range of pipes
@param first iterator to the beginning of the range
@param last iterator to the end of the range
The member function assigns the pipeline to a new range of pipes
specified in <tt>[first, last)</tt> and resets the pipeline to the
initial state. After resetting a pipeline, its token identifier will
start from zero.
*/
void reset(P first, P last);
/**
@brief queries the number of generated tokens in the pipeline
The number represents the total scheduling tokens that has been
generated by the pipeline so far.
*/
size_t num_tokens() const noexcept;
/**
@brief obtains the graph object associated with the pipeline construct
This method is primarily used as an opaque data structure for creating
a module task of the this pipeline.
*/
Graph& graph();
private:
Graph _graph;
size_t _num_tokens;
std::vector<P> _pipes;
std::vector<Task> _tasks;
std::vector<Pipeflow> _pipeflows;
std::unique_ptr<Line[]> _lines;
void _on_pipe(Pipeflow&, Runtime&);
void _build();
Line& _line(size_t, size_t);
};
// constructor
template <typename P>
ScalablePipeline<P>::ScalablePipeline(size_t num_lines) :
_tasks (num_lines + 1),
_pipeflows (num_lines) {
if(num_lines == 0) {
TF_THROW("must have at least one line");
}
_build();
}
// constructor
template <typename P>
ScalablePipeline<P>::ScalablePipeline(size_t num_lines, P first, P last) :
_tasks (num_lines + 1),
_pipeflows (num_lines) {
if(num_lines == 0) {
TF_THROW("must have at least one line");
}
reset(first, last);
_build();
}
// Function: num_lines
template <typename P>
size_t ScalablePipeline<P>::num_lines() const noexcept {
return _pipeflows.size();
}
// Function: num_pipes
template <typename P>
size_t ScalablePipeline<P>::num_pipes() const noexcept {
return _pipes.size();
}
// Function: num_tokens
template <typename P>
size_t ScalablePipeline<P>::num_tokens() const noexcept {
return _num_tokens;
}
// Function: graph
template <typename P>
Graph& ScalablePipeline<P>::graph() {
return _graph;
}
// Function: _line
template <typename P>
typename ScalablePipeline<P>::Line& ScalablePipeline<P>::_line(size_t l, size_t p) {
return _lines[l*num_pipes() + p];
}
// Function: reset
template <typename P>
void ScalablePipeline<P>::reset(P first, P last) {
size_t num_pipes = static_cast<size_t>(std::distance(first, last));
if(num_pipes == 0) {
TF_THROW("pipeline cannot be empty");
}
if(first->type() != PipeType::SERIAL) {
TF_THROW("first pipe must be serial");
}
_pipes.resize(num_pipes);
size_t i=0;
for(auto itr = first; itr != last; itr++) {
_pipes[i++] = itr;
}
_lines = std::make_unique<Line[]>(num_lines() * _pipes.size());
reset();
}
// Function: reset
template <typename P>
void ScalablePipeline<P>::reset() {
_num_tokens = 0;
for(size_t l = 0; l<num_lines(); l++) {
_pipeflows[l]._pipe = 0;
_pipeflows[l]._line = l;
}
_line(0, 0).join_counter.store(0, std::memory_order_relaxed);
for(size_t l=1; l<num_lines(); l++) {
for(size_t f=1; f<num_pipes(); f++) {
_line(l, f).join_counter.store(
static_cast<size_t>(_pipes[f]->type()), std::memory_order_relaxed
);
}
}
for(size_t f=1; f<num_pipes(); f++) {
_line(0, f).join_counter.store(1, std::memory_order_relaxed);
}
for(size_t l=1; l<num_lines(); l++) {
_line(l, 0).join_counter.store(
static_cast<size_t>(_pipes[0]->type()) - 1, std::memory_order_relaxed
);
}
}
// Procedure: _on_pipe
template <typename P>
void ScalablePipeline<P>::_on_pipe(Pipeflow& pf, Runtime&) {
_pipes[pf._pipe]->_callable(pf);
}
// Procedure: _build
template <typename P>
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