Threads, Synchronization and Thread Safety

SyncLock (Monitor) Mutual exclusion within a process Atomic numeric operations Many readers, few writers

Limit concurrency. Async-friendly (WaitAsync).

Mutex (named) Cross-process (single-instance apps) ManualResetEventSlim / AutoResetEvent / CountdownEvent / Barrier Lazy(Of T) / LazyInitializer Thread-safe lazy initialization

ThreadLocal(Of T) / <ThreadStatic> / AsyncLocal(Of T) Per-thread / per-async-flow data Concurrent* collections, ImmutableX Thread-safe data structures

Thread-safety strategies: immutability, confinement (one owner), synchronization, message passing.

Deadlock avoidance: consistent lock ordering, minimal lock scope, no awaiting inside SyncLock (it isn't allowed), use SemaphoreSlim for async critical sections.

UI thread affinity: WinForms Control.Invoke/BeginInvoke, WPF Dispatcher.Invoke, or SynchronizationContext.Post.

Imports System.Threading

Public Class SafeCounter
    Private ReadOnly _gate As New Object()
    Private _count As Integer
    Public Sub Increment()
        SyncLock _gate
            _count += 1
        End SyncLock
    End Sub
    Public ReadOnly Property Count As Integer
        Get
            Return Volatile.Read(_count)
        End Get
    End Property
End Class

Interlocked.Increment(_hits)
Interlocked.CompareExchange(_state, newValue, expected)