Branch Summary: 5159-nc-deadlock

This branch fixes several thread-safety issues and deadlocks reported in issues #5159, #5161, and #5162.

Closes #5159, #5161, and #5162.

Issues Addressed

• Lock-order-inversion deadlock in NotificationCenter #5159: NotificationCenter lock order inversion deadlock
• Pipe is not thread-safe #5161: PollSet and Pipe thread-safety issues (data races detected by TSan)
• Add IOLock #5162: General thread synchronization improvements

New Components

IOLock (Foundation/include/Poco/IOLock.h, Foundation/src/IOLock.cpp)

A new lock-free synchronization primitive for coordinating I/O operations with close/shutdown:

• IOLock - tracks whether an I/O operation is in progress and whether close has been requested
• ScopedIOLock - RAII wrapper that enters on construction and leaves on destruction
• Uses std::atomic<bool> for _closed and _inProgress flags
• Provides markClosed(), wait(), tryWait(), and close() methods

ScopedSocketReactor (Net/include/Poco/Net/SocketReactor.h)

A new RAII wrapper utility class that starts a SocketReactor in a background thread and automatically stops/joins on destruction:

ScopedSocketReactor reactor;
reactor->addEventHandler(socket, observer);
// reactor runs in background thread
// automatically stopped and joined when reactor goes out of scope

Bug Fixes

NotificationCenter (#5159)

• Fixed lock order inversion deadlock in observer notification

Pipe (#5161)

• Added IOLock synchronization for thread-safe read/write operations
• Fixed close ordering: write end must be closed before read end to send EOF to blocked readers
• Fixed race condition: wait() for I/O completion now happens before closing file descriptors
• Affects both POSIX and Windows implementations

PollSet (#5161)

• Added IOLock to coordinate poll() with destructor
• Prevents use-after-free when poll() is running during destruction
• Exit early on poll error when closed
• Affects epoll, poll, and select implementations

Test Improvements

New Tests

• PipeTest - comprehensive test suite including testCloseRace for concurrent close/read
• testConcurrentHandlerRemoval in SocketReactorTest - tests concurrent handler removal

CI Enhancements

• Added sanitized builds (ASan, TSan, UBSan) to CI workflow

Files Changed

Key Code Changes

Pipe Close Sequence (Before)

void PipeImpl::closeRead() {
    if (_readfd != -1) close(fd);      // Race: close while read() in progress
}

Pipe Close Sequence (After)

void PipeImpl::closeRead() {
    _readLock.markClosed();
    _readLock.wait();              // Wait for any in-progress read to finish
    int fd = _readfd.exchange(-1);
    if (fd != -1) close(fd);       // Now safe to close
}

Destructor Close Order (Before)

~PipeImpl() {
    closeRead();   // Wrong: blocks readers waiting for data
    closeWrite();
}

Destructor Close Order (After)

~PipeImpl() {
    closeWrite();  // Correct: sends EOF to unblock readers
    closeRead();
}