RFR: 6478546: FileInputStream.read() throws OutOfMemoryError when there is plenty available

[Vyom Tewari]

On Fri, 21 Jul 2023 22:40:00 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

> Limit native memory allocation and move write loop from the native layer into Java. This change should make the OOME reported in the issue much less likely.

src/java.base/share/native/libjava/io_util.c line 99:

> 97:         return 0;
> 98:     } else if (len > BUF_SIZE) {
> 99:         if (len > MAX_MALLOC_SIZE)

Hi Brian if I am reading code correctly then with the current code change FIS.read(byte[] b, int off, int len) will always read (MAX_MALLOC_SIZE 2097152) bytes if len > MAX_MALLOC_SIZE. 

The java doc of read  as below

public int read(byte[] b,
                int off,
                int len)
         throws IOException
Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read. The number of bytes actually read is returned as an integer.

I think  if you are limiting the internal dynamic buffer to 2097152 byte then you have  to at least attempt to read as many as len bytes if possible before returning.

If I simply the run the following code 

	    int size = 501 * 501 * 501 * 3;

            FileInputStream fis = new FileInputStream("/home/vyom1/test.img"); // Any file with size >= 501*501*501*2

            System.out.println("size: " + size);

            byte buf[] = new byte[size];

            System.out.println("buf ok");

            int bytesRead = fis.read(buf, 0, size);
            System.out.println("Bytes read " + bytesRead);

It will always print “Bytes read 2097152” which is not as per Java specification of InputStream.read(byte[]b, int off, int len).

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PR Review Comment: https://git.openjdk.org/jdk/pull/14981#discussion_r1271976654