github.com/unicornultrafoundation/go-ethereum@v1.9.7-0.20191031044858-21506be82b68/les/execqueue.go (about)

     1  // Copyright 2017 The go-ethereum Authors
     2  // This file is part of the go-ethereum library.
     3  //
     4  // The go-ethereum library is free software: you can redistribute it and/or modify
     5  // it under the terms of the GNU Lesser General Public License as published by
     6  // the Free Software Foundation, either version 3 of the License, or
     7  // (at your option) any later version.
     8  //
     9  // The go-ethereum library is distributed in the hope that it will be useful,
    10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
    11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    12  // GNU Lesser General Public License for more details.
    13  //
    14  // You should have received a copy of the GNU Lesser General Public License
    15  // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
    16  
    17  package les
    18  
    19  import "sync"
    20  
    21  // execQueue implements a queue that executes function calls in a single thread,
    22  // in the same order as they have been queued.
    23  type execQueue struct {
    24  	mu        sync.Mutex
    25  	cond      *sync.Cond
    26  	funcs     []func()
    27  	closeWait chan struct{}
    28  }
    29  
    30  // newExecQueue creates a new execution queue.
    31  func newExecQueue(capacity int) *execQueue {
    32  	q := &execQueue{funcs: make([]func(), 0, capacity)}
    33  	q.cond = sync.NewCond(&q.mu)
    34  	go q.loop()
    35  	return q
    36  }
    37  
    38  func (q *execQueue) loop() {
    39  	for f := q.waitNext(false); f != nil; f = q.waitNext(true) {
    40  		f()
    41  	}
    42  	close(q.closeWait)
    43  }
    44  
    45  func (q *execQueue) waitNext(drop bool) (f func()) {
    46  	q.mu.Lock()
    47  	if drop && len(q.funcs) > 0 {
    48  		// Remove the function that just executed. We do this here instead of when
    49  		// dequeuing so len(q.funcs) includes the function that is running.
    50  		q.funcs = append(q.funcs[:0], q.funcs[1:]...)
    51  	}
    52  	for !q.isClosed() {
    53  		if len(q.funcs) > 0 {
    54  			f = q.funcs[0]
    55  			break
    56  		}
    57  		q.cond.Wait()
    58  	}
    59  	q.mu.Unlock()
    60  	return f
    61  }
    62  
    63  func (q *execQueue) isClosed() bool {
    64  	return q.closeWait != nil
    65  }
    66  
    67  // canQueue returns true if more function calls can be added to the execution queue.
    68  func (q *execQueue) canQueue() bool {
    69  	q.mu.Lock()
    70  	ok := !q.isClosed() && len(q.funcs) < cap(q.funcs)
    71  	q.mu.Unlock()
    72  	return ok
    73  }
    74  
    75  // queue adds a function call to the execution queue. Returns true if successful.
    76  func (q *execQueue) queue(f func()) bool {
    77  	q.mu.Lock()
    78  	ok := !q.isClosed() && len(q.funcs) < cap(q.funcs)
    79  	if ok {
    80  		q.funcs = append(q.funcs, f)
    81  		q.cond.Signal()
    82  	}
    83  	q.mu.Unlock()
    84  	return ok
    85  }
    86  
    87  // clear drops all queued functions
    88  func (q *execQueue) clear() {
    89  	q.mu.Lock()
    90  	q.funcs = q.funcs[:0]
    91  	q.mu.Unlock()
    92  }
    93  
    94  // quit stops the exec queue.
    95  // quit waits for the current execution to finish before returning.
    96  func (q *execQueue) quit() {
    97  	q.mu.Lock()
    98  	if !q.isClosed() {
    99  		q.closeWait = make(chan struct{})
   100  		q.cond.Signal()
   101  	}
   102  	q.mu.Unlock()
   103  	<-q.closeWait
   104  }