Task dependency graph?

[tsung-wei-huang]

Any example or tutorial to how to use fastflow build a task dependency graph? ff_taskf tutorial page is blank with TBD. I didn't find any example either.

[massimotorquati]

You can have a look at the ff_mdf patter (Macro Data-Flow).

[tsung-wei-huang]

I tried to compile the hetero_traversal.cpp example from the tutorial page:

#include <ff/mdf.hpp> 
using namespace ff; 
const size_t SIZE = 1<<8; //1<<20; 
void sum2(long *X, long *Y, const long size); 
void sum3(long *X, long *Y, long *Z, const long size); 
template<typename T>  
struct Parameters { 
    long *A,*B,*C,*D; 
    T* mdf; 
}; 
void taskGen(Parameters<ff_mdf > *const P){ 
  long *A = P->A;  long *B = P->B; 
  long *C = P->C;  long *D = P->D; 
  auto mdf = P->mdf; 
 
  std::vector<param_info> Param; 
  // A = A + B; 
  {   
    const param_info _1={(uintptr_t)A,INPUT};  // 1st param 
    const param_info _2={(uintptr_t)B,INPUT};  // 2nd param 
    const param_info _3={(uintptr_t)A,OUTPUT}; // 3rd param 
    // pack the parameters in one single vector 
    Param.push_back(_1); Param.push_back(_2); 
    Param.push_back(_3); 
    mdf->AddTask(Param, sum2, A,B,SIZE); // create on task 
  }   
  // C = C + B; 
  {   
    Param.clear(); 
    const param_info _1={(uintptr_t)C,INPUT}; 
    const param_info _2={(uintptr_t)B,INPUT}; 
    const param_info _3={(uintptr_t)C,OUTPUT}; 
    Param.push_back(_1); Param.push_back(_2); Param.push_back(_3); 
    mdf->AddTask(Param, sum2, C,B,SIZE); 
  }   
  // D = D + B; 
  {   
    Param.clear(); 
    const param_info _1={(uintptr_t)D,INPUT}; 
    const param_info _2={(uintptr_t)B,INPUT}; 
    const param_info _3={(uintptr_t)D,OUTPUT};
    Param.push_back(_1); Param.push_back(_2); Param.push_back(_3);
    mdf->AddTask(Param, sum2, D,B,SIZE);
  }
  // D = A + C + D; 
  {
    Param.clear();
    const param_info _1={(uintptr_t)A,INPUT};
    const param_info _2={(uintptr_t)C,INPUT};
    const param_info _3={(uintptr_t)D,INPUT};
    const param_info _4={(uintptr_t)D,OUTPUT};
    Param.push_back(_1); Param.push_back(_2);
    Param.push_back(_3); Param.push_back(_4);
    mdf->AddTask(Param, sum3, D,A,C,SIZE);
  }
}
int main() {
  long *A= new long[SIZE], *B= new long[SIZE];
  long *C= new long[SIZE], *D= new long[SIZE];
  for(size_t i=0;i<SIZE;++i) {
    A[i]=i; B[i]=i+1; C[i]=i+2; D[i]=i+3;
  }
  // creates the mdf object passing the task generetor function 
  Parameters<ff_mdf > P;
  ff_mdf dag(taskGen, &P);
  P.A=A,P.B=B,P.C=C,P.D=D,P.mdf=&dag;

  if (dag.run_and_wait_end() <0) {
    std::cerr << "error dag\n";
  }
  return 0;
}

And I use the following command:

~$ g++ hetero_traversal -I fastflow_home/ -pthread

/usr/bin/ld: /tmp/cc80DX8e.o: in function `taskGen(Parameters<ff::ff_mdf>*)':
hetero_traversal.cpp:(.text+0x1289): undefined reference to `sum2(long*, long*, long)'
/usr/bin/ld: hetero_traversal.cpp:(.text+0x1357): undefined reference to `sum2(long*, long*, long)'
/usr/bin/ld: hetero_traversal.cpp:(.text+0x141c): undefined reference to `sum2(long*, long*, long)'
/usr/bin/ld: hetero_traversal.cpp:(.text+0x151c): undefined reference to `sum3(long*, long*, long*, long)'
/usr/bin/ld: /tmp/cc80DX8e.o: in function `ff::ff_pipeline::prepare()::{lambda()#1}::operator()() const':
hetero_traversal.cpp:(.text._ZZN2ff11ff_pipeline7prepareEvENKUlvE_clEv[_ZZN2ff11ff_pipeline7prepareEvENKUlvE_clEv]+0x47): undefined reference to `ff::isa2a_getfirstset(ff::ff_node*)'
/usr/bin/ld: /tmp/cc80DX8e.o: in function `ff::ff_pipeline::prepare()::{lambda()#2}::operator()() const':
hetero_traversal.cpp:(.text._ZZN2ff11ff_pipeline7prepareEvENKUlvE0_clEv[_ZZN2ff11ff_pipeline7prepareEvENKUlvE0_clEv]+0x47): undefined reference to `ff::isa2a_getfirstset(ff::ff_node*)'
/usr/bin/ld: /tmp/cc80DX8e.o: in function `ff::ff_pipeline::prepare()::{lambda()#3}::operator()() const':
hetero_traversal.cpp:(.text._ZZN2ff11ff_pipeline7prepareEvENKUlvE1_clEv[_ZZN2ff11ff_pipeline7prepareEvENKUlvE1_clEv]+0x11d): undefined reference to `ff::isa2a_getsecondset(ff::ff_node*)'
/usr/bin/ld: /tmp/cc80DX8e.o: in function `ff::ff_pipeline::prepare()::{lambda()#4}::operator()() const':
hetero_traversal.cpp:(.text._ZZN2ff11ff_pipeline7prepareEvENKUlvE2_clEv[_ZZN2ff11ff_pipeline7prepareEvENKUlvE2_clEv]+0x11a): undefined reference to `ff::isa2a_getsecondset(ff::ff_node*)'
/usr/bin/ld: /tmp/cc80DX8e.o: in function `ff::ff_pipeline::prepare()':
hetero_traversal.cpp:(.text._ZN2ff11ff_pipeline7prepareEv[_ZN2ff11ff_pipeline7prepareEv]+0x261): undefined reference to `ff::isfarm_withcollector(ff::ff_node*)'
/usr/bin/ld: hetero_traversal.cpp:(.text._ZN2ff11ff_pipeline7prepareEv[_ZN2ff11ff_pipeline7prepareEv]+0x29c): undefined reference to `ff::isfarm_withcollector(ff::ff_node*)'
/usr/bin/ld: hetero_traversal.cpp:(.text._ZN2ff11ff_pipeline7prepareEv[_ZN2ff11ff_pipeline7prepareEv]+0x102d): undefined reference to `ff::isa2a_getfirstset(ff::ff_node*)'
/usr/bin/ld: hetero_traversal.cpp:(.text._ZN2ff11ff_pipeline7prepareEv[_ZN2ff11ff_pipeline7prepareEv]+0x1a41): undefined reference to `ff::isa2a_getfirstset(ff::ff_node*)'
collect2: error: ld returned 1 exit status

Why? I know I have to define sum2 and sum3 but I have no clue about other errors

[tsung-wei-huang]

Perhaps, you may let me know how to program a very simple example of three tasks, A, B, and C, and I want A to run before B and C (B and C can run concurrently). What is the code to express this very simple example?

[massimotorquati]

Hi,
Concerning your code above that does not compile you have to:

1. #include <ff/ff.hpp> (this include must be always included)
2. include the iostream include
3. compile with -std=c++17 flag
4. define sum2 and sum3
   then it compiles with no error/warning:
   g++ -std=c++17 -Wall -I ~/fastflow hetero_traversal.cpp -o hetero -pthread