os::socket_available(int fd, jint *pbytes)

openjdk7-hotspot os.hpp

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//Linux版(jdk7/hotspot/src/os/linux/vm/os_linux.cpp)
int os::socket_available(int fd, jint *pbytes) {
  // Linux doc says EINTR not returned, unlike Solaris
  int ret = ::ioctl(fd, FIONREAD, pbytes);

  //%% note ioctl can return 0 when successful, JVM_SocketAvailable
  // is expected to return 0 on failure and 1 on success to the jdk.
  return (ret < 0) ? 0 : 1;
}