Talk:cpp/chrono/duration

std::chrono::duration could not company with openmpi MPI_gather

following code will be wrong when we use more than 10 threads

```
#include <iostream>
```
```
#include "mpi.h"
```
```
#include "stdlib.h"
```
```
#include <thread>
```
```
#include <chrono>
```
```
#include "stdlib.h"
```
```
using namespace std;
```
```
 
```
```
 
```
```
void delay( int max_time){
```
```
    srand(time(0));
```
```
    int sleepnum = rand()%max_time;
```

    std::chrono::milliseconds dura(sleepnum);

```
    this_thread::sleep_for(dura);
```
```
}
```
```
 
```
```
int main(){
```
```
    MPI_Init(NULL,NULL);
```
```
    int size, rank;
```

    MPI_Comm_rank(MPI_COMM_WORLD,&rank);

    MPI_Comm_size(MPI_COMM_WORLD,&size);

```
    double local_num;
```

    double* buffer = new double[(size)*sizeof(double)  ];

```
    cout<<"pin1\n";
```

    auto start = std::chrono::high_resolution_clock::now();

```
    cout<<"pin2\n";	
```
```
//    for(int i = 0 ; i < 1000; i++)
```
```
    {
```
```
        cout<<"pin3\n";
```
```
        //delay(1000);
```
```
 
```

        MPI_Gather((void*)&local_num,1,MPI_DOUBLE,(void*)buffer,size,MPI_DOUBLE,0,MPI_COMM_WORLD);

```
        if(rank == 0){
```
```
            //delay(100);
```
```
        }
```
```
        cout<<"pin4\n";
```

        //MPI_Bcast(&local_num, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);

```
        cout<<"pin5\n";
```
```
    }
```

    auto end = std::chrono::high_resolution_clock::now();

    std::chrono::duration<double, std::milli> elapsed = end-start;

    std::cout << "use " << elapsed.count() << " ms\n";

```
    //delete[] buffer;
```
```
    MPI_Finalize();
```
```
}
```

I fixed the formatting for the above, but I don't think this belongs here - this isn't stackoverflow. MPI coding is complicated and I wouldn't be surprised if there were a bug or two in the above code.

I think it should be removed.

Hadriel (talk) 14:10, 12 December 2019 (PST)

[edit] ADL and Duration Literals

Is there a way to get argument dependent lookup to work with duration literals? If so, that would be a nice example. This would avoid the need to add a using statement just to use a literal somewhere.

e.g.

 void foo(std::chrono::duration d) {
 }
 
 ...
 
 foo(10ms); // 10ms is understood to be a std::chrono::duration, so no using is required

68.249.219.17 15:52, 29 December 2021 (PST)

ADL would let you find foo if it were defined in namespace std or std::chrono or in the class std::chrono::duration when given an std::chrono::duration argument. The opposite direction of having a function that takes an argument from std::chrono::duration, that has no bearing on how the argument is interpreted when calling foo(argument). Tl;dr ADL changes the function called, not the argument. --Ybab321 (talk) 04:22, 30 December 2021 (PST)

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Talk:cpp/chrono/duration

[edit] ADL and Duration Literals

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