On Thu, 5 May 2022 23:39:30 GMT, Brian Burkhalter <b...@openjdk.org> wrote:
>> Modify native multi-byte read-write code used by the `java.io` classes to
>> limit the size of the allocated native buffer thereby decreasing off-heap
>> memory footprint and increasing throughput.
>
> Brian Burkhalter has updated the pull request with a new target base due to a
> merge or a rebase. The incremental webrev excludes the unrelated changes
> brought in by the merge/rebase. The pull request contains four additional
> commits since the last revision:
>
> - 6478546: Clean up io_util.c
> - Merge
> - 6478546: Decrease malloc'ed buffer maximum size to 64 kB
> - 6478546: FileInputStream.read() throws OutOfMemoryError when there is
> plenty available
src/java.base/share/native/libjava/io_util.c line 79:
> 77: jint off, jint len, jfieldID fid)
> 78: {
> 79: char stackBuf[STACK_BUF_SIZE];
This was in the original code already, but doesn't this always allocate 8k on
the stack, regardless of whether this buffer will be used (if len > 8k or len
== 0)? Wouldn't it be better to allocate this only in the `else` case?
Would apply to the write code as well.
src/java.base/share/native/libjava/io_util.c line 81:
> 79: char stackBuf[STACK_BUF_SIZE];
> 80: char *buf = NULL;
> 81: jint buf_size, read_size;;
minor: double semi colon
src/java.base/share/native/libjava/io_util.c line 129:
> 127: off += n;
> 128: } else if (n == -1) {
> 129: JNU_ThrowIOExceptionWithLastError(env, "Read error");
The original code would have `nread` set to `-1` here, and thus exit with `-1`.
The new code would exit with the last value for `nread` which could be
anything.
src/java.base/share/native/libjava/io_util.c line 201:
> 199: write_size = len < buf_size ? len : buf_size;
> 200: (*env)->GetByteArrayRegion(env, bytes, off, write_size,
> (jbyte*)buf);
> 201: if (!(*env)->ExceptionOccurred(env)) {
Wouldn't this result in an infinite loop if `GetByteArrayRegion` triggered an
exception and `len > 0` ? It would never enter the `if` and `len` is never
changed then...
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PR: https://git.openjdk.java.net/jdk/pull/8235
