parallel processing - Issue with clEnqueueReadBuffer Function in OpenCL - in an Array Sum Sample -


everyone, i'm beginner on opencl , wrote simple code in c sums 2 arrays. here part of code:

// create kernel.  cl_kernel kernelsum = clcreatekernel( myprogram, "sum", &error );   // set input array.  size_t arraysize = 1000;  char* = ( char* ) malloc( sizeof( char ) * arraysize ); char* b = ( char* ) malloc( sizeof( char ) * arraysize ); char* c = ( char* ) malloc( sizeof( char ) * arraysize );  (int = 0; < arraysize; += 1) {     a[ ] = 1;     b[ ] = 2;     c[ ] = -1; }   // set buffers.  cl_mem a_buffer = clcreatebuffer(     mycontext,     cl_mem_read_only | cl_mem_copy_host_ptr,     arraysize * sizeof( char ), a,     &error );  cl_mem b_buffer = clcreatebuffer(     mycontext,     cl_mem_read_only | cl_mem_copy_host_ptr,     arraysize * sizeof( char ), b,     &error );  cl_mem c_buffer = clcreatebuffer(     mycontext,     cl_mem_write_only,     arraysize * sizeof( char ), null,     &error );  printf( "buffers created.\n" );   // setting kernel arguments.  error = clsetkernelarg( kernelsum, 0, sizeof( cl_mem ), &a_buffer );  error |= clsetkernelarg( kernelsum, 1, sizeof( cl_mem ), &b_buffer );  error |= clsetkernelarg( kernelsum, 2, sizeof( cl_mem ), &c_buffer );  printf( "arguments set.\n" );   // enqueue kernels execute.  cl_event event;  size_t globalworkoffset = 0;  size_t globalworksize[ 1 ] = { arraysize };  size_t localworksize[ 1 ] = { 1 };  clenqueuendrangekernel(     mycommandqueue,     kernelsum,     1,                  // work_dim     0,              // global work offset     globalworksize,     localworksize,              // local work offset     0, null,     &event     );  printf( "kernel enqueued.\n" );  error = clenqueuereadbuffer(     mycommandqueue,     c_buffer,     cl_true,                        // blocking option     ( size_t ) 0, arraysize * sizeof( char ),   // offset, data_size     c,                              // host_ptr     0, null,     &event );  if ( error != cl_success ) {     printf( "buffer reading failed.\n" );     exit( 1 ); }

however, got incorrect result : numbers in "c" array zeros. thought has clenqueuereadbuffer, or perhaps not. ideas issue? expecting suggestions! :-)

your call clenqueuereadbuffer not wait kernel finish. execute simultaneously kernel. change call to:

error = clenqueuereadbuffer(     mycommandqueue,     c_buffer,     cl_true,                        // blocking option     ( size_t ) 0, arraysize * sizeof( char ),   // offset, data_size     c,                              // host_ptr     1, &event,     null );

this cause clenqueuereadbuffer wait kernel event finish before starting read buffer.


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