Optional<Reflector> Reflector::create(size_t size)
{
static const char *path = "reflector.shm";
FileDescriptor fd;
void *lower = nullptr;
void *upper = nullptr;
void *both = nullptr;
int sts = -1;
if ((size == 0) || (size % 4096)) {
return Optional<Reflector>();
}
fd.reset(shm_open(path, O_RDWR | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR));
if (fd.empty()) {
return Optional<Reflector>();
}
sts = shm_unlink(path);
if (sts < 0) {
return Optional<Reflector>();
}
sts = ftruncate(fd.get(), size);
if (sts < 0) {
return Optional<Reflector>();
}
both = mmap(nullptr, size * 2, PROT_READ | PROT_WRITE, MAP_SHARED, fd.get(), 0);
if (both == MAP_FAILED) {
return Optional<Reflector>();
}
lower = mremap(both, size * 2, size, 0);
if (lower == MAP_FAILED) {
sts = munmap(both, size * 2);
assert(sts >= 0);
return Optional<Reflector>();
}
else if (lower != both) {
sts = munmap(lower, size);
assert(sts);
return Optional<Reflector>();
}
upper = static_cast<uint8_t*>(lower) + size;
upper = mmap(upper, size, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_FIXED, fd.get(), 0);
if (upper == MAP_FAILED) {
sts = munmap(lower, size);
assert(sts >= 0);
return Optional<Reflector>();
}
return Optional<Reflector>(Reflector(std::move(fd), lower, size));
}
MMap::MMap (const FileDescriptor& fd, bool const sequential)
:
size (fd.size()),
ptr (mmap (NULL, size, PROT_READ|PROT_WRITE,
MAP_SHARED|MAP_NORESERVE, fd.get(), 0)),
mapped (ptr != GU_MAP_FAILED)
{
if (!mapped)
{
gu_throw_error(errno) << "mmap() on '" << fd.name()
<< "' failed";
}
#if !defined(__sun__) && !defined(__APPLE__) && !defined(__FreeBSD__)
/* Solaris, Darwin, and FreeBSD do not have MADV_DONTFORK */
if (posix_madvise (ptr, size, MADV_DONTFORK))
{
int const err(errno);
log_warn << "Failed to set MADV_DONTFORK on " << fd.name()
<< ": " << err << " (" << strerror(err) << ")";
}
#endif
/* benefits are questionable */
if (sequential && posix_madvise (ptr, size, MADV_SEQUENTIAL))
{
int const err(errno);
log_warn << "Failed to set MADV_SEQUENTIAL on " << fd.name()
<< ": " << err << " (" << strerror(err) << ")";
}
log_debug << "Memory mapped: " << ptr << " (" << size << " bytes)";
}