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Asked: 2026-06-08T22:27:27+00:00

I am trying to write a simple parallel_for using pthreads. Original code is something

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I am trying to write a simple parallel_for using pthreads.
Original code is something like this.

#ifdef HAVE_TBB
 template<typename Body> static inline
 void parallel_for( const BlockedRange& range, const Body& body )
 {
        tbb::parallel_for(range, body);
 }
#else
 template<typename Body> static inline
 void parallel_for( const BlockedRange& range, const Body& body )
 {      
        body(range); 
 }
#endif

I rewrite for the case TBB does not exist. Here is what I have written. I have problem compiling it. threadFunc gives errors when I write template<typename Body> before it. 

In function 'void cv::parallel_for(const cv::BlockedRange&, const Body&)':
error: no matches converting function 'threadFunc' to type 'void* (*)(void*)'
error: candidates are: template<class Body> void* cv::threadFunc(void*)

These are the error messages I get. There must be a simple fix probably. Thanks.

struct MyStruct {
    BlockedRange range;
    Body& body;
};

//template<typename Body>
static void* threadFunc(void *arg) {
    MyStruct<Body> *rangeBody = (MyStruct<Body>*) arg;
    rangeBody->body(rangeBody->range);
}

template<typename Body> static inline
void parallel_for( const BlockedRange& range, const Body& body )
{
    BlockedRange& range1 = BlockedRange(range.begin(), range.end()/2);
    BlockedRange& range2 = BlockedRange(range.end()/2, range.end());

    MyStruct<Body> rangeBody1; 
    rangeBody1.range = range1; 
    rangeBody1.body = body;

    MyStruct<Body> rangeBody2; 
    rangeBody2.range = range2; 
    rangeBody2.body = body;

    pthread_t thread1, thread2;
    pthread_create(&thread1, NULL, threadFunc, (void*) &rangeBody1);
    pthread_create(&thread2, NULL, threadFunc, (void*) &rangeBody2);
    pthread_join( thread1, NULL);
    pthread_join( thread2, NULL);    
}
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1 Answer

  1. Editorial Team

    If threadFunc is a function template, then you need to specialise it to get a function as required:

    pthread_create(&thread1, NULL, threadFunc<Body>, &rangeBody1);
                                         ^^^^^^
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