Go's Sync

// Mutex provides mutual exclusion for shared resources.
type Mutex struct {
    state int32   // State of the mutex (locked/unlocked)
    sema  uint32  // Semaphore for blocking goroutines
}

// Lock acquires the mutex, blocking if necessary.
func (m *Mutex) Lock() {
    // Check if already locked; if so, block until unlocked.
}

// Unlock releases the mutex.
func (m *Mutex) Unlock() {
    // Update state and unblock waiting goroutines if any.
}

// RWMutex allows multiple readers or one writer.
type RWMutex struct {
    w       Mutex   // Mutex for exclusive access by writers
    readers int32   // Count of active readers
    readerSem uint32 // Semaphore for managing reader access
    writerSem uint32 // Semaphore for managing writer access
}

// RLock acquires a read lock, allowing multiple concurrent readers.
func (rw *RWMutex) RLock() {
    // Increment reader count; block if a writer is active.
}

// RUnlock releases a read lock.
func (rw *RWMutex) RUnlock() {
    // Decrement reader count and unblock if necessary.
}

// Lock acquires an exclusive write lock.
func (rw *RWMutex) Lock() {
    // Block all readers and wait for exclusive access.
}

// Unlock releases the write lock.
func (rw *RWMutex) Unlock() {
    // Release exclusive access and notify waiting readers/writers.
}

// WaitGroup waits for a collection of goroutines to finish executing.
type WaitGroup struct {
    noCopy noCopy     // Prevent copying of WaitGroup
    state1 [1]uint32  // Atomic state tracking active goroutines
    done   uint32     // Count of completed goroutines
    sema   uint32     // Semaphore for blocking
}

// Add increments the WaitGroup counter by n.
func (wg *WaitGroup) Add(n int) {
    // Increment counter; block if necessary based on done count.
}

// Done decrements the WaitGroup counter by one.
func (wg *WaitGroup) Done() {
    // Increment done count; signal if all goroutines are done.
}

// Wait blocks until the WaitGroup counter is zero.
func (wg *WaitGroup) Wait() {
    // Block until all added goroutines call Done().
}

// Once ensures that a function is executed only once.
type Once struct {
    m    Mutex   // Mutex for synchronization
    done uint32  // Flag indicating if function has been called
}

// Do executes the function f only once.
func (o *Once) Do(f func()) {
    o.m.Lock()          // Lock to ensure exclusive access
    if o.done == 0 {   // Check if function has been executed
        f()            // Call the function
        o.done = 1    // Mark as executed
    }
    o.m.Unlock()       // Unlock after execution
}

// Cond provides a way for goroutines to wait for conditions to be met.
type Cond struct {
    noCopy noCopy      // Prevent copying of Cond
    L      *Mutex      // Locker that must be held when calling Wait or Signal
    notify notifyList  // List of waiting goroutines
}

// Wait atomically releases the mutex and waits for notification.
func (c *Cond) Wait() {
    c.L.Unlock()       // Unlock before waiting to avoid deadlock
    // Block until notified by Signal or Broadcast.
}

// Signal wakes one waiting goroutine, if any.
func (c *Cond) Signal() {
    // Notify one waiting goroutine to wake up.
}

// Broadcast wakes all waiting goroutines, if any.
func (c *Cond) Broadcast() {
    // Notify all waiting goroutines to wake up.
}

type Map struct {
   mu     Mutex
   read   atomic.Value // readOnly
   dirty  map[interface{}]*entry
   misses int
}

type readOnly struct {
   m       map[interface{}]*entry
   amended bool
}

type entry struct {
   p unsafe.Pointer // *interface{}
}