__declspec(noinline) void PointerToDurableMappedFile::makeChunkWritable(size_t chunkno) {
stdx::lock_guard<stdx::mutex> lkPrivateViews(_m);
if (writable.get(chunkno)) // double check lock
return;
// remap all maps in this chunk.
// common case is a single map, but could have more than one with smallfiles or .ns files
size_t chunkStart = chunkno * MemoryMappedCOWBitset::ChunkSize;
size_t chunkNext = chunkStart + MemoryMappedCOWBitset::ChunkSize;
stdx::lock_guard<stdx::mutex> lkMapView(mapViewMutex);
map<void*, DurableMappedFile*>::iterator i = _views.upper_bound((void*)(chunkNext - 1));
while (1) {
const pair<void*, DurableMappedFile*> x = *(--i);
DurableMappedFile* mmf = x.second;
if (mmf == 0)
break;
size_t viewStart = reinterpret_cast<size_t>(x.first);
size_t viewEnd = viewStart + mmf->length();
if (viewEnd <= chunkStart)
break;
size_t protectStart = std::max(viewStart, chunkStart);
dassert(protectStart < chunkNext);
size_t protectEnd = std::min(viewEnd, chunkNext);
size_t protectSize = protectEnd - protectStart;
dassert(protectSize > 0 && protectSize <= MemoryMappedCOWBitset::ChunkSize);
DWORD oldProtection;
bool ok = VirtualProtect(
reinterpret_cast<void*>(protectStart), protectSize, PAGE_WRITECOPY, &oldProtection);
if (!ok) {
DWORD dosError = GetLastError();
if (dosError == ERROR_COMMITMENT_LIMIT) {
// System has run out of memory between physical RAM & page file, tell the user
BSONObjBuilder bb;
ProcessInfo p;
p.getExtraInfo(bb);
severe() << "MongoDB has exhausted the system memory capacity.";
severe() << "Current Memory Status: " << bb.obj();
}
severe() << "VirtualProtect for " << mmf->filename() << " chunk " << chunkno
<< " failed with " << errnoWithDescription(dosError) << " (chunk size is "
<< protectSize << ", address is " << hex << protectStart << dec << ")"
<< " in mongo::makeChunkWritable, terminating" << endl;
fassertFailed(16362);
}
}
writable.set(chunkno);
}
