extract Semaphore to utils package

irc/channel.go

 	userLimit         int
 	accountToUMode    map[string]modes.Mode
 	history           history.Buffer
-	stateMutex        sync.RWMutex // tier 1
-	writerSemaphore   Semaphore    // tier 1.5
-	joinPartMutex     sync.Mutex   // tier 3
-	ensureLoaded      utils.Once   // manages loading stored registration info from the database
+	stateMutex        sync.RWMutex    // tier 1
+	writerSemaphore   utils.Semaphore // tier 1.5
+	joinPartMutex     sync.Mutex      // tier 3
+	ensureLoaded      utils.Once      // manages loading stored registration info from the database
 	dirtyBits         uint
 }
 

irc/semaphores.go

 package irc
 
 import (
-	"log"
 	"runtime"
-	"runtime/debug"
+
+	"github.com/oragono/oragono/irc/utils"
 )
 
 // See #237 for context. Operations that might allocate large amounts of temporary
 	MaxServerSemaphoreCapacity = 32
 )
 
-// Semaphore is a counting semaphore. Note that a capacity of n requires O(n) storage.
-type Semaphore (chan bool)
-
 // ServerSemaphores includes a named Semaphore corresponding to each concurrency-limited
 // sever operation.
 type ServerSemaphores struct {
 	// each distinct operation MUST have its own semaphore;
 	// methods that acquire a semaphore MUST NOT call methods that acquire another
-	ClientDestroy Semaphore
+	ClientDestroy utils.Semaphore
 }
 
 // Initialize initializes a set of server semaphores.
 	serversem.ClientDestroy.Initialize(capacity)
 	return
 }
-
-// Initialize initializes a semaphore to a given capacity.
-func (semaphore *Semaphore) Initialize(capacity int) {
-	*semaphore = make(chan bool, capacity)
-	for i := 0; i < capacity; i++ {
-		(*semaphore) <- true
-	}
-}
-
-// Acquire acquires a semaphore, blocking if necessary.
-func (semaphore *Semaphore) Acquire() {
-	<-(*semaphore)
-}
-
-// TryAcquire tries to acquire a semaphore, returning whether the acquire was
-// successful. It never blocks.
-func (semaphore *Semaphore) TryAcquire() (acquired bool) {
-	select {
-	case <-(*semaphore):
-		return true
-	default:
-		return false
-	}
-}
-
-// Release releases a semaphore. It never blocks. (This is not a license
-// to program spurious releases.)
-func (semaphore *Semaphore) Release() {
-	select {
-	case (*semaphore) <- true:
-		// good
-	default:
-		// spurious release
-		log.Printf("spurious semaphore release (full to capacity %d)", cap(*semaphore))
-		debug.PrintStack()
-	}
-}

irc/socket.go

 	"strings"
 	"sync"
 	"time"
+
+	"github.com/oragono/oragono/irc/utils"
 )
 
 var (
 	maxSendQBytes int
 
 	// this is a trylock enforcing that only one goroutine can write to `conn` at a time
-	writerSemaphore Semaphore
+	writerSemaphore utils.Semaphore
 
 	buffers       [][]byte
 	totalLength   int

irc/utils/semaphores.go

+// Copyright (c) 2018 Shivaram Lingamneni
+
+package utils
+
+import (
+	"log"
+	"runtime/debug"
+)
+
+// Semaphore is a counting semaphore. Note that a capacity of n requires O(n) storage.
+// A semaphore of capacity 1 can be used as a trylock.
+type Semaphore (chan bool)
+
+// Initialize initializes a semaphore to a given capacity.
+func (semaphore *Semaphore) Initialize(capacity int) {
+	*semaphore = make(chan bool, capacity)
+	for i := 0; i < capacity; i++ {
+		(*semaphore) <- true
+	}
+}
+
+// Acquire acquires a semaphore, blocking if necessary.
+func (semaphore *Semaphore) Acquire() {
+	<-(*semaphore)
+}
+
+// TryAcquire tries to acquire a semaphore, returning whether the acquire was
+// successful. It never blocks.
+func (semaphore *Semaphore) TryAcquire() (acquired bool) {
+	select {
+	case <-(*semaphore):
+		return true
+	default:
+		return false
+	}
+}
+
+// Release releases a semaphore. It never blocks. (This is not a license
+// to program spurious releases.)
+func (semaphore *Semaphore) Release() {
+	select {
+	case (*semaphore) <- true:
+		// good
+	default:
+		// spurious release
+		log.Printf("spurious semaphore release (full to capacity %d)", cap(*semaphore))
+		debug.PrintStack()
+	}
+}