Unix: synchronize encryption fragment exceptions

Serialize updates to the shared exception pointer and retain the first
reported error. Test concurrent failures through all three handlers,
exception cleanup and subsequent successful work.

Tests/test_encryption_thread_pool_exceptions.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+"""Check concurrent fragment exceptions in the production Unix encryption pool.
+
+Uses real pool, encryption-mode dispatch and platform synchronization code with
+an event-controlled test cipher. Requires Linux, Python 3 and a C++11 compiler.
+Run: python3 Tests/test_encryption_thread_pool_exceptions.py [--sanitize]
+"""
+import argparse
+import os
+from pathlib import Path
+import shlex
+import subprocess
+import sys
+import tempfile
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("--build-dir", type=Path)
+    parser.add_argument("--sanitize", action="store_true", help="enable AddressSanitizer")
+    args = parser.parse_args()
+    if not sys.platform.startswith("linux"):
+        parser.error("This build runner requires Linux")
+    build = (args.build_dir or Path(tempfile.mkdtemp(prefix="vc-pool-exceptions-"))).resolve()
+    build.mkdir(parents=True, exist_ok=True)
+    sources = ["Volume/EncryptionThreadPool.cpp", "Volume/EncryptionMode.cpp"]
+    sources += ["Platform/" + name + ".cpp" for name in (
+        "Buffer", "Exception", "Memory", "Serializable", "Serializer", "SerializerFactory",
+        "StringConverter", "Unix/Mutex", "Unix/SyncEvent", "Unix/SystemException",
+        "Unix/SystemLog", "Unix/Thread")]
+    exe = build / "encryption_thread_pool_exception_test"
+    command = shlex.split(os.environ.get("CXX", "c++")) + [
+        "-std=c++11", "-O2", "-g", "-pthread", "-ffunction-sections", "-fdata-sections",
+        "-Wl,--gc-sections", "-DTC_UNIX", "-DTC_LINUX", "-DARGON2_NO_THREADS",
+        "-D_FILE_OFFSET_BITS=64", "-I" + str(ROOT / "src"),
+        "-I" + str(ROOT / "src/Crypto"), "-I" + str(ROOT / "src/Crypto/Argon2/include")]
+    if args.sanitize:
+        command += ["-fsanitize=address", "-fno-omit-frame-pointer"]
+    command += [str(ROOT / "Tests/encryption_thread_pool_exception_test.cpp")]
+    command += [str(ROOT / "src" / source) for source in sources]
+    command += ["-o", str(exe)]
+    result = subprocess.run(command, capture_output=True, text=True, timeout=180)
+    (build / "build.log").write_text(result.stdout + result.stderr)
+    if result.returncode:
+        raise RuntimeError(result.stdout + result.stderr)
+    result = subprocess.run([str(exe)], timeout=60)
+    if result.returncode not in (0, 77):
+        raise SystemExit(result.returncode)
+
+
+if __name__ == "__main__":
+    main()