c# - Would using the Parallel class improve performance when copying scanline from bitmap to bitmap? -


i need copy scanlines 1 byte* buffer byte* buffer different strides.

to i'm using rtlmovememory :

[dllimport("kernel32.dll", entrypoint = "rtlmovememory", setlasterror = false)] private static unsafe extern void movememory(void* dest, void* src, int size);

the normal way like

for (int y = 0; y < height; y++ ) {     movememory(dst_ptr, src_ptr, stride);     src_ptr += src_stride;     dst_ptr += dst_stride; }

my question - faster using parallel class ?

parallel.for(0, height, (y) => {     byte* src_ptr = src_base + y * src_stride;     byte* dst_ptr = dst_base + y * dst_stride;     movememory(dst_ptr, src_ptr, line_width); });

or impact performance negatively ?

actually, testing shows copying line-by-line faster. example, created array representing 1024 x 768 bitmap. parallel version 45% faster.

the parallel version faster when scan lines longer. below 1 kilobytes, single-threaded version faster.

tested .net 4.5, visual studio 2013. 64 bit mode. compiled release, , run without debugger attached.

    private const int numlines = 1024;     private const int linelength = 768*3;     private const int arraysize = numlines*linelength;     [dllimport("kernel32.dll", entrypoint = "rtlmovememory", setlasterror = false)]     private static unsafe extern void movememory(void* dest, void* src, int size);     unsafe public void test()     {         // initialize big array test copy         var source = enumerable.range(0, arraysize).select(x => (byte)x).toarray();         var dest = new byte[arraysize];          fixed (byte* psource = source, pdest = dest)         {             // test single threaded             // once jit             console.writeline("testing single threaded...");             movesinglethread(psource, pdest, numlines, linelength);              // okay, time it.             var sw = stopwatch.startnew();             movesinglethread(psource, pdest, numlines, linelength);             sw.stop();             console.writeline("single threaded: {0:n0} ticks", sw.elapsedticks);             var singleticks = sw.elapsedticks;              console.writeline("testing parallel");             // once jit             moveparallel(psource, pdest, numlines, linelength);              sw = stopwatch.startnew();             moveparallel(psource, pdest, numlines, linelength);             sw.stop();             console.writeline("parallel: {0:n0} ticks", sw.elapsedticks);              var diff = sw.elapsedticks - singleticks;             var pct = (double) sw.elapsedticks/singleticks;             console.writeline("difference: {0:n0} ticks {1:p2}", diff, pct);         }      }      private unsafe void movesinglethread(byte* source, byte* dest, int nlines, int linelength)     {         var srcptr = source;         var dstptr = dest;         (int y = 0; y < nlines; ++y)         {             movememory(dstptr, srcptr, linelength);             srcptr += linelength;             dstptr += linelength;         }     }      unsafe void moveparallel(byte* source, byte* dest, int nlines, int linelength)     {         parallel.for(0, nlines, (y) =>         {             byte* srcptr = source + y * linelength;             byte* dstptr = dest + y * linelength;             movememory(dstptr, srcptr, linelength);         });     }

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