tyler-hardin/thread_pool

Thread pool using std::* primitives from C++20, with optional priority queue/greenthreading for POSIX.

thread_pool's Issues

How to pass a multiple arguments to my function?

I tried something like

...
int myFunc(int a, int b, int c)
...
... myPool.async(std::function<int(int, int, int)>(myFunc), a, b, c)...

and get a ton of errors.
But if I using function with 1 argument everything works well.
What i'm doing wrong?

High CPU usage

I integrated thread_pool in one of our projects and replaced the current threading mechanism.
Instead of creating new threads I wanted to reuse the threads. It was fairly easy to migrate to this lib, but I am experiencing high CPU load, when the thread pool is not used.

Function wrapper

My Function:

http://paste.ofcode.org/3bdy7AXyHgpshzqEi95HavJ

help me thanks

Test as number of threads decreased : infinite loop?

I simplified the original test code to be the following

test.cpp.gz

`#include "thread_pool.hpp"
#include <vector>
#include <iostream> // std::cout, std::endl
using namespace std;

/*

• Intel Xeon ES-1620 v3 3.5GHz
• git clone https://github.com/Tyler-Hardin/thread_pool.git
• git checkout -b cv origin/cv
• $ gcc --version
• gcc.exe (Rev3, Built by MSYS2 project) 6.3.0
• $ g++ --std=c++11 test.cpp thread_pool.cpp
• $ time ./a.exe
• ...
• real 5m23.883s for num_threads = 1 (aborted manually)
• real 3m55.198s for num_threads = 2 (aborted manually)
• why do above configurations never finish but the ones below do finish?
• Further, if add "-O3" to compiler option above, the run in 26s and 13s,why?
• real 0m12.690s for num_threads = 3
• real 0m9.199s for num_threads = 4
• real 0m7.971s for num_threads = 5
• real 0m7.654s for num_threads = 6
• real 0m7.304s for num_threads = 7
• real 0m7.740s for num_threads = 8
  */

bool func_bool_int(int n) {
if(n < 2)
return false;
for(int i = 2;i < n;i++)
if(n % i == 0)
return false;
return true;
}

int main() {

const int num_threads = 4;
thread_pool p(num_threads);

int n = 100000;
int max = 5 * n;
vector<future<bool>> f;
for( int i = n; i < max; i++ )
	f.emplace_back(p.async(function<bool(int)>(func_bool_int), i));

std::cout << "..." << std::endl;
size_t accum = 0;
for(auto &i : f) {
accum += i.get();
}
std::cout << "accum = " << accum << std::endl;

return 0;

}
`

When I ran for num_threads = 8, 7, 6, 5, 4, 3 things went okay. But when I tried num_threads of 2 or 1 the runtime seemed to be in an infinite loop ie I was seeing about 7s to 12s runtimes above num_threads>2 but once I tried num_threads=2 or 1 I waited 3 minutes to 5 minutes (orders of magnitude longer than extrapolated runtime) before manually killing the process. Is this behavior to be expected? Note this was on a gcc 6.3 with "git checkout -b cv origin/cv" branch. Adding an "-O3" optimazation seemed to fix the issue; expected?

Compilation warning Wsign-compare

Very silly, but annoying; I get a:

thread_pool.hpp:107:19: warning: comparison of integer expressions of different signedness: ‘int’ and ‘unsigned int’ [-Wsign-compare]

warning, which is easily silenced by:

- for(int i = 0;i < num_threads;i++){
+ for(unsigned int i = 0;i < num_threads;i++){

C++20 build failure

I get this when using C++20:

thread_pool.hpp:13:9: warning: the 'bool' keyword is not allowed in a C++20 concept definition 13 | concept bool Callable = requires(Fn f, Args... args) {

Error: underined reference to thread_pool::...

(Edited by Tyler to show error that OP had before he deleted the comment):
...
main.cpp:(.text+0x31b): undefined reference to 'thread_pool::~thread_pool()'
...

Waiting for threads to finish

Hello,

How do I wait for threads to finish?

I've got this:

    fut.emplace_back(tp.async(std::function<int(std::string)>(breakPacket), completePacket));

I push into it about 3000 items for the threads ti process, but then I don't know how to wait for the threads to finish...

Thanks!

David