code.gitea.io/gitea@v1.19.3/modules/sync/exclusive_pool.go (about)

     1  // Copyright 2016 The Gogs Authors. All rights reserved.
     2  // SPDX-License-Identifier: MIT
     3  
     4  package sync
     5  
     6  import (
     7  	"sync"
     8  )
     9  
    10  // ExclusivePool is a pool of non-identical instances
    11  // that only one instance with same identity is in the pool at a time.
    12  // In other words, only instances with different identities can be in
    13  // the pool the same time. If another instance with same identity tries
    14  // to get into the pool, it hangs until previous instance left the pool.
    15  //
    16  // This pool is particularly useful for performing tasks on same resource
    17  // on the file system in different goroutines.
    18  type ExclusivePool struct {
    19  	lock sync.Mutex
    20  
    21  	// pool maintains locks for each instance in the pool.
    22  	pool map[string]*sync.Mutex
    23  
    24  	// count maintains the number of times an instance with same identity checks in
    25  	// to the pool, and should be reduced to 0 (removed from map) by checking out
    26  	// with same number of times.
    27  	// The purpose of count is to delete lock when count down to 0 and recycle memory
    28  	// from map object.
    29  	count map[string]int
    30  }
    31  
    32  // NewExclusivePool initializes and returns a new ExclusivePool object.
    33  func NewExclusivePool() *ExclusivePool {
    34  	return &ExclusivePool{
    35  		pool:  make(map[string]*sync.Mutex),
    36  		count: make(map[string]int),
    37  	}
    38  }
    39  
    40  // CheckIn checks in an instance to the pool and hangs while instance
    41  // with same identity is using the lock.
    42  func (p *ExclusivePool) CheckIn(identity string) {
    43  	p.lock.Lock()
    44  
    45  	lock, has := p.pool[identity]
    46  	if !has {
    47  		lock = &sync.Mutex{}
    48  		p.pool[identity] = lock
    49  	}
    50  	p.count[identity]++
    51  
    52  	p.lock.Unlock()
    53  	lock.Lock()
    54  }
    55  
    56  // CheckOut checks out an instance from the pool and releases the lock
    57  // to let other instances with same identity to grab the lock.
    58  func (p *ExclusivePool) CheckOut(identity string) {
    59  	p.lock.Lock()
    60  	defer p.lock.Unlock()
    61  
    62  	p.pool[identity].Unlock()
    63  	if p.count[identity] == 1 {
    64  		delete(p.pool, identity)
    65  		delete(p.count, identity)
    66  	} else {
    67  		p.count[identity]--
    68  	}
    69  }