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-rw-r--r--klm/util/fake_ofstream.hh94
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diff --git a/klm/util/fake_ofstream.hh b/klm/util/fake_ofstream.hh
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+/* Like std::ofstream but without being incredibly slow. Backed by a raw fd.
+ * Does not support many data types. Currently, it's targeted at writing ARPA
+ * files quickly.
+ */
+#include "util/double-conversion/double-conversion.h"
+#include "util/double-conversion/utils.h"
+#include "util/file.hh"
+#include "util/scoped.hh"
+#include "util/string_piece.hh"
+
+#define BOOST_LEXICAL_CAST_ASSUME_C_LOCALE
+#include <boost/lexical_cast.hpp>
+
+namespace util {
+class FakeOFStream {
+ public:
+ static const std::size_t kOutBuf = 1048576;
+
+ // Does not take ownership of out.
+ explicit FakeOFStream(int out)
+ : buf_(util::MallocOrThrow(kOutBuf)),
+ builder_(static_cast<char*>(buf_.get()), kOutBuf),
+ // Mostly the default but with inf instead. And no flags.
+ convert_(double_conversion::DoubleToStringConverter::NO_FLAGS, "inf", "NaN", 'e', -6, 21, 6, 0),
+ fd_(out) {}
+
+ ~FakeOFStream() {
+ if (buf_.get()) Flush();
+ }
+
+ FakeOFStream &operator<<(float value) {
+ // Odd, but this is the largest number found in the comments.
+ EnsureRemaining(double_conversion::DoubleToStringConverter::kMaxPrecisionDigits + 8);
+ convert_.ToShortestSingle(value, &builder_);
+ return *this;
+ }
+
+ FakeOFStream &operator<<(double value) {
+ EnsureRemaining(double_conversion::DoubleToStringConverter::kMaxPrecisionDigits + 8);
+ convert_.ToShortest(value, &builder_);
+ return *this;
+ }
+
+ FakeOFStream &operator<<(StringPiece str) {
+ if (str.size() > kOutBuf) {
+ Flush();
+ util::WriteOrThrow(fd_, str.data(), str.size());
+ } else {
+ EnsureRemaining(str.size());
+ builder_.AddSubstring(str.data(), str.size());
+ }
+ return *this;
+ }
+
+ // Inefficient! TODO: more efficient implementation
+ FakeOFStream &operator<<(unsigned value) {
+ return *this << boost::lexical_cast<std::string>(value);
+ }
+
+ FakeOFStream &operator<<(char c) {
+ EnsureRemaining(1);
+ builder_.AddCharacter(c);
+ return *this;
+ }
+
+ // Note this does not sync.
+ void Flush() {
+ util::WriteOrThrow(fd_, buf_.get(), builder_.position());
+ builder_.Reset();
+ }
+
+ // Not necessary, but does assure the data is cleared.
+ void Finish() {
+ Flush();
+ // It will segfault trying to null terminate otherwise.
+ builder_.Finalize();
+ buf_.reset();
+ util::FSyncOrThrow(fd_);
+ }
+
+ private:
+ void EnsureRemaining(std::size_t amount) {
+ if (static_cast<std::size_t>(builder_.size() - builder_.position()) <= amount) {
+ Flush();
+ }
+ }
+
+ util::scoped_malloc buf_;
+ double_conversion::StringBuilder builder_;
+ double_conversion::DoubleToStringConverter convert_;
+ int fd_;
+};
+
+} // namespace