+namespace {
+
+void readRandomDevice(void* data, size_t size) {
+#ifdef _MSC_VER
+ static folly::once_flag flag;
+ static HCRYPTPROV cryptoProv;
+ folly::call_once(flag, [&] {
+ if (!CryptAcquireContext(
+ &cryptoProv,
+ nullptr,
+ nullptr,
+ PROV_RSA_FULL,
+ CRYPT_VERIFYCONTEXT)) {
+ if (GetLastError() == NTE_BAD_KEYSET) {
+ // Mostly likely cause of this is that no key container
+ // exists yet, so try to create one.
+ PCHECK(CryptAcquireContext(
+ &cryptoProv, nullptr, nullptr, PROV_RSA_FULL, CRYPT_NEWKEYSET));
+ } else {
+ LOG(FATAL) << "Failed to acquire the default crypto context.";
+ }
+ }
+ });
+ CHECK(size <= std::numeric_limits<DWORD>::max());
+ PCHECK(CryptGenRandom(cryptoProv, (DWORD)size, (BYTE*)data));
+#else
+ // Keep the random device open for the duration of the program.
+ static int randomFd = ::open("/dev/urandom", O_RDONLY);
+ PCHECK(randomFd >= 0);
+ auto bytesRead = readFull(randomFd, data, size);
+ PCHECK(bytesRead >= 0 && size_t(bytesRead) == size);
+#endif
+}
+
+class BufferedRandomDevice {
+ public:
+ static constexpr size_t kDefaultBufferSize = 128;
+
+ explicit BufferedRandomDevice(size_t bufferSize = kDefaultBufferSize);
+
+ void get(void* data, size_t size) {
+ if (LIKELY(size <= remaining())) {
+ memcpy(data, ptr_, size);
+ ptr_ += size;
+ } else {
+ getSlow(static_cast<unsigned char*>(data), size);
+ }
+ }
+
+ private:
+ void getSlow(unsigned char* data, size_t size);
+
+ inline size_t remaining() const {
+ return size_t(buffer_.get() + bufferSize_ - ptr_);
+ }
+
+ const size_t bufferSize_;
+ std::unique_ptr<unsigned char[]> buffer_;
+ unsigned char* ptr_;
+};
+
+BufferedRandomDevice::BufferedRandomDevice(size_t bufferSize)
+ : bufferSize_(bufferSize),
+ buffer_(new unsigned char[bufferSize]),
+ ptr_(buffer_.get() + bufferSize) { // refill on first use
+}
+
+void BufferedRandomDevice::getSlow(unsigned char* data, size_t size) {
+ DCHECK_GT(size, remaining());
+ if (size >= bufferSize_) {
+ // Just read directly.
+ readRandomDevice(data, size);
+ return;
+ }
+
+ size_t copied = remaining();
+ memcpy(data, ptr_, copied);
+ data += copied;
+ size -= copied;
+
+ // refill
+ readRandomDevice(buffer_.get(), bufferSize_);
+ ptr_ = buffer_.get();
+
+ memcpy(data, ptr_, size);
+ ptr_ += size;
+}
+
+struct RandomTag {};
+
+} // namespace
+
+void Random::secureRandom(void* data, size_t size) {
+ static SingletonThreadLocal<BufferedRandomDevice, RandomTag>
+ bufferedRandomDevice;
+ bufferedRandomDevice.get().get(data, size);
+}
+
+class ThreadLocalPRNG::LocalInstancePRNG {
+ public:
+ LocalInstancePRNG() : rng(Random::create()) {}
+
+ Random::DefaultGenerator rng;
+};
+
+ThreadLocalPRNG::ThreadLocalPRNG() {
+ static SingletonThreadLocal<ThreadLocalPRNG::LocalInstancePRNG, RandomTag>
+ localInstancePRNG;
+ local_ = &localInstancePRNG.get();