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78 lines
2.5 KiB
78 lines
2.5 KiB
3 years ago
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// Copyright (C) MongoDB, Inc. 2022-present.
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may
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// not use this file except in compliance with the License. You may obtain
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// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
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// Package randutil provides common random number utilities.
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package randutil
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import (
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crand "crypto/rand"
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"fmt"
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"io"
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"math/rand"
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"sync"
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)
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// A LockedRand wraps a "math/rand".Rand and is safe to use from multiple goroutines.
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type LockedRand struct {
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mu sync.Mutex
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r *rand.Rand
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}
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// NewLockedRand returns a new LockedRand that uses random values from src to generate other random
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// values. It is safe to use from multiple goroutines.
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func NewLockedRand(src rand.Source) *LockedRand {
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return &LockedRand{
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// Ignore gosec warning "Use of weak random number generator (math/rand instead of
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// crypto/rand)". We intentionally use a pseudo-random number generator.
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/* #nosec G404 */
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r: rand.New(src),
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}
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}
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// Read generates len(p) random bytes and writes them into p. It always returns len(p) and a nil
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// error.
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func (lr *LockedRand) Read(p []byte) (int, error) {
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lr.mu.Lock()
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n, err := lr.r.Read(p)
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lr.mu.Unlock()
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return n, err
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}
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// Intn returns, as an int, a non-negative pseudo-random number in the half-open interval [0,n). It
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// panics if n <= 0.
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func (lr *LockedRand) Intn(n int) int {
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lr.mu.Lock()
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x := lr.r.Intn(n)
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lr.mu.Unlock()
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return x
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}
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// Shuffle pseudo-randomizes the order of elements. n is the number of elements. Shuffle panics if
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// n < 0. swap swaps the elements with indexes i and j.
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//
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// Note that Shuffle locks the LockedRand, so shuffling large collections may adversely affect other
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// concurrent calls. If many concurrent Shuffle and random value calls are required, consider using
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// the global "math/rand".Shuffle instead because it uses much more granular locking.
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func (lr *LockedRand) Shuffle(n int, swap func(i, j int)) {
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lr.mu.Lock()
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lr.r.Shuffle(n, swap)
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lr.mu.Unlock()
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}
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// CryptoSeed returns a random int64 read from the "crypto/rand" random number generator. It is
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// intended to be used to seed pseudorandom number generators at package initialization. It panics
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// if it encounters any errors.
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func CryptoSeed() int64 {
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var b [8]byte
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_, err := io.ReadFull(crand.Reader, b[:])
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if err != nil {
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panic(fmt.Errorf("failed to read 8 bytes from a \"crypto/rand\".Reader: %v", err))
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}
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return (int64(b[0]) << 0) | (int64(b[1]) << 8) | (int64(b[2]) << 16) | (int64(b[3]) << 24) |
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(int64(b[4]) << 32) | (int64(b[5]) << 40) | (int64(b[6]) << 48) | (int64(b[7]) << 56)
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}
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