k8s.io/apiserver@v0.31.1/pkg/storage/cacher/time_budget.go (about)

     1  /*
     2  Copyright 2016 The Kubernetes Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package cacher
    18  
    19  import (
    20  	"sync"
    21  	"time"
    22  
    23  	"k8s.io/utils/clock"
    24  )
    25  
    26  const (
    27  	refreshPerSecond = 50 * time.Millisecond
    28  	maxBudget        = 100 * time.Millisecond
    29  )
    30  
    31  // timeBudget implements a budget of time that you can use and is
    32  // periodically being refreshed. The pattern to use it is:
    33  //
    34  //	budget := newTimeBudget(...)
    35  //	...
    36  //	timeout := budget.takeAvailable()
    37  //	// Now you can spend at most timeout on doing stuff
    38  //	...
    39  //	// If you didn't use all timeout, return what you didn't use
    40  //	budget.returnUnused(<unused part of timeout>)
    41  //
    42  // NOTE: It's not recommended to be used concurrently from multiple threads -
    43  // if first user takes the whole timeout, the second one will get 0 timeout
    44  // even though the first one may return something later.
    45  type timeBudget interface {
    46  	takeAvailable() time.Duration
    47  	returnUnused(unused time.Duration)
    48  }
    49  
    50  type timeBudgetImpl struct {
    51  	sync.Mutex
    52  	clock     clock.Clock
    53  	budget    time.Duration
    54  	maxBudget time.Duration
    55  	refresh   time.Duration
    56  	// last store last access time
    57  	last time.Time
    58  }
    59  
    60  func newTimeBudget() timeBudget {
    61  	result := &timeBudgetImpl{
    62  		clock:     clock.RealClock{},
    63  		budget:    time.Duration(0),
    64  		refresh:   refreshPerSecond,
    65  		maxBudget: maxBudget,
    66  	}
    67  	result.last = result.clock.Now()
    68  	return result
    69  }
    70  
    71  func (t *timeBudgetImpl) takeAvailable() time.Duration {
    72  	t.Lock()
    73  	defer t.Unlock()
    74  	// budget accumulated since last access
    75  	now := t.clock.Now()
    76  	acc := now.Sub(t.last).Seconds() * t.refresh.Seconds()
    77  	if acc < 0 {
    78  		acc = 0
    79  	}
    80  	// update current budget and store the current time
    81  	if t.budget = t.budget + time.Duration(acc*1e9); t.budget > t.maxBudget {
    82  		t.budget = t.maxBudget
    83  	}
    84  	t.last = now
    85  	result := t.budget
    86  	t.budget = time.Duration(0)
    87  	return result
    88  }
    89  
    90  func (t *timeBudgetImpl) returnUnused(unused time.Duration) {
    91  	t.Lock()
    92  	defer t.Unlock()
    93  	if unused < 0 {
    94  		// We used more than allowed.
    95  		return
    96  	}
    97  	// add the unused time directly to the budget
    98  	// takeAvailable() will take into account the elapsed time
    99  	if t.budget = t.budget + unused; t.budget > t.maxBudget {
   100  		t.budget = t.maxBudget
   101  	}
   102  }