RFR: 6478546: FileInputStream.read() throws OutOfMemoryError when there is plenty available [v2]

[Alan Bateman]

On Tue, 25 Jul 2023 23:50:07 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.
>
> Brian Burkhalter has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - 6478546: Decrease malloc limit to 1.5 MB
>  - 6478546: Minor refactoring
>  - 6478546: Prevent short read

I looked through the latest version (69941de4).

I think the main issue with this version is that it changes behavior of the read methods to work like "read fully", I don't think we should do that. To preserve long standing behavior it should attempt a second/subsequent read when the clamped buffer is filled. I think this is close to what you want here:

    private int readBytes(byte[] b, final int off, int len) throws IOException {
        Objects.checkFromIndexSize(off, len, b.length);
        int nread = 0;
        int pos = off;
        int remaining = len;
        do {
            int size = Math.min(remaining, 64 * 1024);
            try {
                int n = readBytes0(b, pos, size);
                if (n < 0) {
                    // EOF
                    break;
                }
                nread += n;
                if (n < size) {
                    // buffer not filled
                    break;
                }
                pos += n;
                remaining -= n;
            } catch (IOException ioe) {
                if (nread > 0) {
                    break;
                }
                throw ioe;
            }
        } while (remaining > 0);
        return nread;
    }


The changes in 69941de4 are also using nested blockers, this is benign, but if this code is change then they can be dropped from the callers.

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PR Comment: https://git.openjdk.org/jdk/pull/14981#issuecomment-1651352313