// Copyright (c) 2018 Shivaram Lingamneni package irc import ( "log" "runtime" "runtime/debug" ) // See #237 for context. Operations that might allocate large amounts of temporary // garbage, or temporarily tie up some other resource, may cause thrashing unless // their concurrency is artificially restricted. We use `chan bool` as a // (regrettably, unary-encoded) counting semaphore to enforce these restrictions. const ( // this is a tradeoff between exploiting CPU-level parallelism (higher values better) // and not thrashing the allocator (lower values better). really this is all just // guesswork. oragono *can* make use of cores beyond this limit --- just not for // the protected operations. 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 } // Initialize initializes a set of server semaphores. func (serversem *ServerSemaphores) Initialize() { capacity := runtime.NumCPU() if capacity > MaxServerSemaphoreCapacity { capacity = MaxServerSemaphoreCapacity } 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() } }