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- // 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
- }
-
- // NewServerSemaphores creates a new ServerSemaphores.
- func NewServerSemaphores() (result *ServerSemaphores) {
- capacity := runtime.NumCPU()
- if capacity > MaxServerSemaphoreCapacity {
- capacity = MaxServerSemaphoreCapacity
- }
- result = new(ServerSemaphores)
- result.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()
- }
- }
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