parSafe heap can deadlock

[jhh67]

Summary of Problem

A heap created with parSafe=true can deadlock under some sequences of operations, e.g. push followed by pop or top. push followed by push appears to work. I didn't try any other combinations. It wasn't obvious from looking at the code where the problem lies.

Steps to Reproduce

Source Code:

use Heap;

var h = new heap(int, parSafe=true);
h.push(1);
writeln(h.pop());

Compile command:

chpl --no-devel foo.chpl

Execution command:

./foo

Associated Future Test(s):

Configuration Information

• Output of chpl --version:

chpl version 1.26.0 pre-release (27f3d59788)
Copyright 2020-2022 Hewlett Packard Enterprise Development LP
Copyright 2004-2019 Cray Inc.
(See LICENSE file for more details)

• Output of $CHPL_HOME/util/printchplenv --anonymize:

CHPL_TARGET_PLATFORM: darwin
CHPL_TARGET_COMPILER: clang
CHPL_TARGET_ARCH: x86_64
CHPL_TARGET_CPU: native
CHPL_LOCALE_MODEL: flat
CHPL_COMM: none *
CHPL_TASKS: qthreads
CHPL_LAUNCHER: none
CHPL_TIMERS: generic
CHPL_UNWIND: none
CHPL_MEM: jemalloc
CHPL_ATOMICS: cstdlib
CHPL_GMP: none *
CHPL_HWLOC: bundled
CHPL_RE2: bundled
CHPL_LLVM: none *
CHPL_AUX_FILESYS: none

• Back-end compiler and version, e.g. gcc --version or clang --version:

Apple clang version 12.0.0 (clang-1200.0.32.29)
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

• (For Cray systems only) Output of module list: