mirror of
https://github.com/crazybber/awesome-patterns.git
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85 lines
1.6 KiB
Markdown
85 lines
1.6 KiB
Markdown
# Semaphore Pattern
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A semaphore is a synchronization pattern/primitive that imposes mutual exclusion on a limited number of resources.
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## Implementation
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```go
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package semaphore
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var (
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ErrNoTickets = errors.New("semaphore: could not aquire semaphore")
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ErrIllegalRelease = errors.New("semaphore: can't release the semaphore without acquiring it first")
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)
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// Interface contains the behavior of a semaphore that can be acquired and/or released.
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type Interface interface {
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Acquire() error
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Release() error
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}
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type implementation struct {
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sem chan struct{}
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timeout time.Duration
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}
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func (s *implementation) Acquire() error {
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select {
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case s.sem <- struct{}{}:
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return nil
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case <-time.After(s.timeout):
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return ErrNoTickets
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}
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}
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func (s *implementation) Release() error {
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select {
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case _ = <-s.sem:
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return nil
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case <-time.After(s.timeout):
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return ErrIllegalRelease
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}
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return nil
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}
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func New(tickets int, timeout time.Duration) Interface {
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return &implementation{
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sem: make(chan struct{}, tickets),
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timeout: timeout,
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}
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}
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```
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## Usage
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### Semaphore with Timeouts
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```go
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tickets, timeout := 1, 3*time.Second
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s := semaphore.New(tickets, timeout)
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if err := s.Acquire(); err != nil {
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panic(err)
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}
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// Do important work
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if err := s.Release(); err != nil {
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panic(err)
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}
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```
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### Semaphore without Timeouts (Non-Blocking)
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```go
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tickets, timeout := 0, 0
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s := semaphore.New(tickets, timeout)
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if err := s.Acquire(); err != nil {
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if err != semaphore.ErrNoTickets {
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panic(err)
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}
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// No tickets left, can't work :(
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os.Exit(1)
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}
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```
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