Play with Windows MM-functions for potential use in concurrent GC

mem_fun.d

import core.sys.windows.windows, core.stdc.stdlib, 
    std.stdio, std.datetime;
//pragma(mangle, "_QueryWorkingSet@12")
extern(Windows) BOOL QueryWorkingSet(HANDLE hProcess,PVOID pv,DWORD cb);

void main()
{
     // map 512mb, obviously 32bit sucks, as I couldn't map more
    uint SIZE = 2^^29;
    auto mapping = CreateFileMappingA(INVALID_HANDLE_VALUE, 
        null, PAGE_READWRITE | SEC_COMMIT, 0, SIZE, null);
    assert(mapping != INVALID_HANDLE_VALUE);
    void* heap = MapViewOfFile(mapping, FILE_MAP_ALL_ACCESS, 
        0, 0, SIZE);
    assert(heap);
//use the memory
 
    for(size_t n = 0; n<SIZE; n += 4096)
    {
        ubyte* p = cast(ubyte*)heap+n;
        p[0] = 0xFF;
        p[1] = 0xFF;
    }

//"start collection" must stop threads here
    //re-map as primary r-w view for GC ("stash" it)
    void* heap2 = MapViewOfFile(mapping, FILE_MAP_ALL_ACCESS, 
        0, 0, SIZE);
    assert(heap2);
    int code = UnmapViewOfFile(heap);
    assert(code);
    //remap as CoW for the app at the _same_ address
    void* heap3 = MapViewOfFileEx(mapping, FILE_MAP_COPY, 
        0, 0, SIZE, heap);
    assert(heap3 == heap);

//may unpause here

    //do some changes, spoil 1 of 4 pages
    for(size_t n = 0; n<SIZE; n += 4*4096)
    {
        ubyte* p = cast(ubyte*)heap+n; //CoW view
        ubyte* p2 = cast(ubyte*)heap2+n; //GC's original
        assert(p[0] == 0xFF);
        assert(p[1] == 0xFF);
        p[0] = 0x1F;
        assert(p2[0] == 0xFF);
    }

    MEMORY_BASIC_INFORMATION mem;
//this is "mark ended" phase time to collect, again pause

    StopWatch sw;
    size_t regions = 0;
    sw.start();
    //version(VirtQ)
    {    //walk the page ranges
        
        for(size_t off = 0; off < SIZE;)
        {
            size_t written = VirtualQuery(heap+off, &mem, mem.sizeof);
            assert(written);
            size_t size = mem.RegionSize;
            regions++;
            off += size;
            //writefln("%08x:%08x (%d bytes)- flags %x", mem.BaseAddress, 
            //    mem.BaseAddress+size, size, mem.AllocationProtect);
        }
    }
    sw.stop();
    writefln("Checking pages (%d regions) took %d usec", 
        regions, sw.peek.usecs);
}