[apologies for the probably-busted formatting in this mail, but i didn't actually receive the mail i'm replying to.]
Mark Hindess wrote: > Our implementation of BufferedReader calls FileInputStream.available() > while the RI does not. well, it's InputStreamReader's fault, but "yes". > This is a problem because it means that the RI > can read certain types of files that our implementation can not - such > as /proc/mounts on Linux. I will investigate this shortly. indeed. stat(2) will lie to you about many files in /proc too, which confuses people who [ignoring the obvious race] try to allocate a right-sized buffer before they start reading. the kernel really assumes you're going to use the traditional Unix "repeatedly call read(2) until it returns 0 at EOF" idiom. (which is fair enough, since it doesn't know what data it's going to return until you open the file.) > While looking at this I notice that our implementation of > FileInputStream.available() does: > > long currentPosition = fileSystem.seek(fd.descriptor, 0L, > IFileSystem.SEEK_CUR); > long endOfFilePosition = fileSystem.seek(fd.descriptor, 0L, > IFileSystem.SEEK_END); > fileSystem.seek(fd.descriptor, currentPosition, IFileSystem.SEEK_SET); > return (int) (endOfFilePosition - currentPosition); > > making three JNI calls. It might be better to implement this as a > single JNI call - particularly since at the moment we seem to be calling > it more often than the RI. in Android -- where we have a Linux kernel and do want to be able to read files in /proc -- we already went this route. we effectively have an "available" in OSFileSystem. on Linux, we can use the FIONREAD ioctl(2). you already have this code lying around in harmony, but you only use it for stdin and ProcessInputStream. grep for FIONREAD and work your way back. (from my orthodox Unix perspective, distinguishing between regular files and ttys in the Java side is a mistake. only the native code for platforms that make such a distinction should pay for their mistake.) anyway, yeah, an intention-revealing "int OSFileSystem.available(int fd)" for the Java side, and letting the native side worry about how best to implement it sounds like a good idea. -- Elliott Hughes - http://who/enh - http://jessies.org/~enh/
