RFR: 8315351: Rid synchronization in PipedInputStream.close() in favour of benign race

[Sergey Tsypanov]

Assuming that the value written into `in` is always `-1` we can rid synchronized block in favour of guarding `in = - 1` with writing into volatile `closedByReader `:

public void close() throws IOException {
    closedByReader = true;
    synchronized (this) {
        in = -1;
    }
}

-->

public void close() throws IOException {
    in = -1;
    closedByReader = true;
}

-------------

Commit messages:
 - Drop redundant synchronization from PipedInputStream.close()

Changes: https://git.openjdk.org/jdk/pull/15486/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15486&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315351
  Stats: 6 lines in 1 file changed: 1 ins; 3 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15486.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15486/head:pull/15486

PR: https://git.openjdk.org/jdk/pull/15486