Skip to content

D
dlib
Commit b6ae2a6d authored by Davis King's avatar Davis King
Browse files
Options

Improved the thread_pool example program.

parent cf8e3d6f
Hide whitespace changes
Inline Side-by-side
Showing with 111 additions and 94 deletions
examples/thread_pool_ex.cpp
View file @ b6ae2a6d
......@@ -13,6 +13,7 @@
#include "dlib/threads.h"
#include "dlib/misc_api.h" // for dlib::sleep
#include "dlib/logger.h"
#include <vector>
using namespace dlib;
......@@ -33,65 +34,81 @@ thread_pool tp(3);
class test
{
/*
The thread_pool accepts "tasks" from the user and schedules them
for execution in one of its threads when one becomes available. Each
task is just a request to call a member function on a particular object
(or if you use futures you may make tasks that call global functions).
So here we create a class called test with a few member functions which
we will have the thread pool call as tasks.
The thread_pool accepts "tasks" from the user and schedules them for
execution in one of its threads when one becomes available. Each task
is just a request to call a function. So here we create a class called
test with a few member functions which we will have the thread pool call
as tasks.
*/
public:
void task_0()
void task()
{
dlog << LINFO << "task_0 start";
dlog << LINFO << "task start";
// Here we ask the thread pool to call this->subtask() three different times
// with different arguments. Note that calls to add_task() will return
// immediately if there is an available thread to hand the task off to. However,
// if there isn't a thread ready then add_task blocks until there is such a thread.
// Also note that since task_0() is executed within the thread pool (see main() below)
future<int> var;
var = 1;
// Here we ask the thread pool to call this->subtask() and this->subtask2().
// Note that calls to add_task() will return immediately if there is an
// available thread to hand the task off to. However, if there isn't a
// thread ready then add_task() blocks until there is such a thread.
// Also note that since task() is executed within the thread pool (see main() below)
// calls to add_task() will execute the requested task within the calling thread
// in cases where the thread pool is full. This means it is safe to have
// tasks running in the thread pool spawn sub tasks which is what we are doing here.
tp.add_task(*this,&test::subtask,1); // schedule call to this->subtask(1)
tp.add_task(*this,&test::subtask,2); // schedule call to this->subtask(2)
tp.add_task(*this,&test::subtask,3); // schedule call to this->subtask(3)
// wait_for_all_tasks() is a function that blocks until all tasks
// submitted to the thread pool by the thread calling wait_for_all_tasks()
// finish. So this call blocks until the 3 tasks above are done.
// in cases where the thread pool is full. This means it is always safe to
// spawn subtasks from within another task, which is what we are doing here.
tp.add_task(*this,&test::subtask,var); // schedule call to this->subtask(var)
tp.add_task(*this,&test::subtask2); // schedule call to this->subtask2()
// Since var is a future, this line will wait for the test::subtask task to
// finish and before allowing us to access the contents of var. var will
// return the integer it contains. In this case result will be assigned
// the value of 2 since var was incremented by subtask().
int result = var;
// print out the result
dlog << LINFO << "var = " << result;
// Wait for all the tasks we have started to finish. Note that
// wait_for_all_tasks() only waits for tasks which were started
// by the calling thread. So you don't have to worry about other
// unrelated parts of your application interfering. In this case
// it just waits for subtask2() to finish.
tp.wait_for_all_tasks();
dlog << LINFO << "task_0 end" ;
dlog << LINFO << "task end" ;
}
void subtask(long a)
void subtask(int& a)
{
dlib::sleep(200);
dlog << LINFO << "subtask end " << a;
a = a + 1;
dlog << LINFO << "subtask end ";
}
void task_1(long a, long b)
void subtask2()
{
dlog << LINFO << "task_1 start: " << a << ", " << b;
dlib::sleep(700);
dlog << LINFO << "task_1 end: " << a << ", " << b;
dlib::sleep(300);
dlog << LINFO << "subtask2 end ";
}
};
// ----------------------------------------------------------------------------------------
void add (
long a,
long b,
long& result
)
class add_value
{
dlib::sleep(400);
result = a + b;
}
public:
add_value(int value):val(value) { }
void operator()( int& a )
{
a += val;
}
private:
int val;
};
// ----------------------------------------------------------------------------------------
......@@ -100,56 +117,58 @@ int main()
// tell the logger to print out everything
dlog.set_level(LALL);
test a;
dlog << LINFO << "schedule a few tasks";
// schedule a call to a.task_1(10,11)
tp.add_task(a, &test::task_1, 10, 11);
// schedule the thread pool to call a.task_0().
uint64 id = tp.add_task(a, &test::task_0);
test mytask;
// Schedule the thread pool to call mytask.task(). Note that all forms of add_task()
// pass in the task object by reference. This means you must make sure, in this case,
// that mytask isn't destructed until after the task has finished executing.
tp.add_task(mytask, &test::task);
// schedule a call to a.task_1(12,13)
tp.add_task(a, &test::task_1, 12, 13);
// You can also pass task objects to a thread pool by value. So in this case we don't
// have to worry about keeping our own instance of the task. Here we construct a temporary
// add_value object and pass it right in and everything works like it should.
future<int> num = 3;
tp.add_task_by_value(add_value(7), num); // adds 7 to num
int result = num.get();
dlog << LINFO << "result = " << result; // prints result = 10
dlog << LINFO << "wait for a.task_0() to finish";
// now wait for our a.task_0() task to finish. To do this we use the id
// returned by add_task to reference the task we want to wait for.
tp.wait_for_task(id);
dlog << LINFO << "a.task_0() finished, now start another task_1() call";
// schedule a call to a.task_1(14,15)
tp.add_task(a, &test::task_1, 14, 15);
dlog << LINFO << "wait for all tasks to finish";
// here we wait for all tasks which were requested by the main thread
// to complete.
tp.wait_for_all_tasks();
dlog << LINFO << "all tasks finished";
// The thread pool also allows you to use futures to pass arbitrary objects into the tasks.
// For example:
future<long> n1, n2, result;
n1 = 3;
n2 = 4;
// add a task that is supposed to go call add(n1, n2, result);
tp.add_task(add, n1, n2, result);
// uncomment this line if your compiler supports the new C++0x lambda functions
//#define COMPILER_SUPPORTS_CPP0X_LAMBDA_FUNCTIONS
#ifdef COMPILER_SUPPORTS_CPP0X_LAMBDA_FUNCTIONS
// This line will wait for the task in the thread pool to finish and when it does
// result will return the integer it contains. In this case r will be assigned a value of 7.
long r = result;
// print out the result
dlog << LINFO << "result = " << r;
// In the above examples we had to explicitly create task objects which is
// inconvenient. If you have a compiler which supports C++0x lambda functions
// then you can use the following simpler method.
// We can also use futures with member functions like so:
tp.add_task(a, &test::task_1, n1, n2);
// make a task which will just log a message
tp.add_task_by_value([](){
dlog << LINFO << "A message from a lambda function running in another thread.";
});
// and we can still wait for tasks like so:
// Here we make 10 different tasks, each assigns a different value into
// the elements of the vector vect.
std::vector<int> vect(10);
for (unsigned long i = 0; i < vect.size(); ++i)
{
// Make a lambda function which takes vect by reference and i by value. So what
// will happen is each assignment statement will run in a thread in the thread_pool.
tp.add_task_by_value([&vect,i](){
vect[i] = i;
});
}
// Wait for all tasks which were requested by the main thread to complete.
tp.wait_for_all_tasks();
dlog << LINFO << "all tasks using futures finished";
for (unsigned long i = 0; i < vect.size(); ++i)
{
dlog << LINFO << "vect["<<i<<"]: " << vect[i];
}
#endif
......@@ -157,26 +176,24 @@ int main()
the time the log message occurred and the value in [] is the thread id for the thread
that generated the log message):
0 INFO [0] main: schedule a few tasks
0 INFO [1] main: task_1 start: 10, 11
0 INFO [2] main: task_0 start
200 INFO [2] main: subtask end 2
200 INFO [3] main: subtask end 1
200 INFO [3] main: task_1 start: 12, 13
201 INFO [0] main: wait for a.task_0() to finish
400 INFO [2] main: subtask end 3
400 INFO [2] main: task_0 end
400 INFO [0] main: a.task_0() finished, now start another task_1() call
401 INFO [2] main: task_1 start: 14, 15
401 INFO [0] main: wait for all tasks to finish
700 INFO [1] main: task_1 end: 10, 11
901 INFO [3] main: task_1 end: 12, 13
1101 INFO [2] main: task_1 end: 14, 15
1101 INFO [0] main: all tasks finished
1503 INFO [0] main: result = 7
1503 INFO [3] main: task_1 start: 3, 4
2203 INFO [3] main: task_1 end: 3, 4
2203 INFO [0] main: all tasks using futures finished
1 INFO [0] main: schedule a few tasks
1 INFO [1] main: task start
1 INFO [0] main: result = 10
201 INFO [2] main: subtask end
201 INFO [1] main: var = 2
201 INFO [2] main: A message from a lambda function running in another thread.
301 INFO [3] main: subtask2 end
301 INFO [1] main: task end
301 INFO [0] main: vect[0]: 0
301 INFO [0] main: vect[1]: 1
301 INFO [0] main: vect[2]: 2
301 INFO [0] main: vect[3]: 3
301 INFO [0] main: vect[4]: 4
301 INFO [0] main: vect[5]: 5
301 INFO [0] main: vect[6]: 6
301 INFO [0] main: vect[7]: 7
301 INFO [0] main: vect[8]: 8
301 INFO [0] main: vect[9]: 9
*/
}
......
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment