mirror of
https://github.com/ergochat/ergo.git
synced 2025-10-31 13:57:23 +01:00
82 lines
2.3 KiB
Go
82 lines
2.3 KiB
Go
// 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()
|
|
}
|
|
}
|