[crac] RFR: List open FDs through reading /proc/self/fd

[Radim Vansa]

Previously the code was iterating through all possible FD values, up to highest allowed FD number, and required allocation of possibly huge array. Reading /proc/self/fd into a compact array is both more memory efficient and does not require excessive syscalls.

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Commit messages:
 - List open FDs through reading /proc/self/fd

Changes: https://git.openjdk.org/crac/pull/67/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=67&range=00
  Stats: 97 lines in 1 file changed: 21 ins; 18 del; 58 mod
  Patch: https://git.openjdk.org/crac/pull/67.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/67/head:pull/67

PR: https://git.openjdk.org/crac/pull/67