motex

package module
Version: v0.0.0-...-23f15e6 Latest Latest
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Published: Jun 4, 2017 License: MIT Imports: 1 Imported by: 0

Documentation

Overview

Package motex implements a demoteable and promoteable exclusion lock. Demoteable meaning a write lock can be changed to a read lock. Promoteable meaning a demoted write lock can be changed back to a write lock.

If Demote() and Promote() are never called, motex behaves identically to a sync.RWMutex.

A demoted lock continues to block calls to Lock, but calls to RLock will not block.

non-atomic read and update with sync.Mutex:

var mu sync.Mutex
var state int
mu.RLock()
copied := state
mu.RUnlock()
copied += 1 // ... do something resource intensive to modify the copied state.
mu.Lock()
state = copied
mu.Unlock()

atomic read and update with motex.Motex:

var mo motex.Motex
var state int
mo.Lock()
mo.Demote()
copied := state
copied += 1 // ... do something resource intensive to modiy the copied state.
mo.Promote()
state = copied
mo.Unlock()

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

This section is empty.

Types

type Motex

type Motex struct {
	// contains filtered or unexported fields
}

A Motex is a demoteable and promoteable exclusion lock.

A Motex must not be copied after first use.

func (*Motex) Demote

func (m *Motex) Demote()

Demote demotes m from a Lock() for writing to a lock for reading, unblocking any calls to RLock. Other calls to Lock will continue to block. It is a run-time error if m is not currently locked for writing. It is also a run-time error if m is locked for writing but demoted on entry to Demote.

A demoted lock is not equivalent to an RLock. Only demoted locks can be promoted.

func (*Motex) Lock

func (m *Motex) Lock()

Lock locks m for writing. If the lock is already locked for reading or writing, Lock blocks until the lock is available (i.e. after Unlock or RUnlock is called).

func (*Motex) Promote

func (m *Motex) Promote()

Promote promotes m from a Demoted() Lock() to a lock for writing, blocking all calls to RLock. If the lock is already RLocked, Promote blocks until the lock is available (i.e. after RUnlock is called). It is a run-time error if m is not currently a demoted lock.

A demoted lock is not equivalent to an RLock. Only demoted locks can be promoted.

func (*Motex) RLock

func (m *Motex) RLock()

RLock locks m for reading. If the lock is already locked for writing or demoted reading, RLock blocks until the lock is available (i.e. after Unlock is called).

func (*Motex) RUnlock

func (m *Motex) RUnlock()

RUnlock unlocks m for reading. It is a run-time error if m is not locked for reading on entry to RUnlock.

func (*Motex) Unlock

func (m *Motex) Unlock()

Unlock unlocks m for writing. It is a run-time error if m is not locked for writing on entry to Unlock. It is also a run-time error if m is locked for writing but demoted on entry to Unlock.

Source Files

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