github.com/m3db/m3@v1.5.0/src/dbnode/storage/limits/permits/permit.go (about)

     1  // Copyright (c) 2021 Uber Technologies, Inc.
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE.
    20  
    21  package permits
    22  
    23  import (
    24  	"go.uber.org/atomic"
    25  	"go.uber.org/zap"
    26  
    27  	"github.com/m3db/m3/src/x/instrument"
    28  )
    29  
    30  // permit tracks the quota used by a caller and provides basic sanity checks that a caller
    31  // correctly uses the permit.
    32  type permit struct {
    33  	// immutable state
    34  	quota int64
    35  	iOpts instrument.Options
    36  
    37  	// mutable state
    38  	quotaUsed int64
    39  	// refCount is used to check if a caller incorrectly double releases/acquires a permit. the value should
    40  	// always be 0 (nobody holds the permit) or 1 (somebody holds the permit).
    41  	refCount atomic.Int32
    42  }
    43  
    44  // NewPermit constructs a new Permit with the provided quota.
    45  func NewPermit(quota int64, iOpts instrument.Options) Permit {
    46  	return &permit{
    47  		quota: quota,
    48  		iOpts: iOpts,
    49  	}
    50  }
    51  
    52  func (p *permit) PostRelease() {
    53  	if p.iOpts != nil && p.refCount.Dec() != 0 {
    54  		instrument.EmitAndLogInvariantViolation(p.iOpts, func(l *zap.Logger) {
    55  			l.Error("permit released more than once")
    56  		})
    57  	}
    58  }
    59  
    60  func (p *permit) PreAcquire() {
    61  	if p.iOpts != nil && p.refCount.Inc() != 1 {
    62  		instrument.EmitAndLogInvariantViolation(p.iOpts, func(l *zap.Logger) {
    63  			l.Error("permit acquired more than once")
    64  		})
    65  	}
    66  	p.quotaUsed = 0
    67  }
    68  
    69  // AllowedQuota is the amount of quota the caller can use with this Permit.
    70  func (p *permit) AllowedQuota() int64 {
    71  	return p.quota
    72  }
    73  
    74  // QuotaRemaining is the amount of remaining quota for this Permit. Can be negative if the caller used more quota
    75  // than they were allowed.
    76  func (p *permit) QuotaRemaining() int64 {
    77  	return p.quota - p.quotaUsed
    78  }
    79  
    80  // Use adds the quota to the total used quota.
    81  func (p *permit) Use(quota int64) {
    82  	p.quotaUsed += quota
    83  }