mirror of
https://github.com/featurebasedb/featurebase.git
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68 lines
2.1 KiB
Go
68 lines
2.1 KiB
Go
// Copyright 2017 Pilosa Corp.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package syswrap wraps syscalls (just mmap right now) in order to impose a
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// global in-process limit on the maximum number of active mmaps.
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package syswrap
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import (
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"sync"
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"sync/atomic"
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"syscall"
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"github.com/pkg/errors"
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)
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var mapCount uint64
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var ErrMaxMapCountReached = errors.New("maximum map count reached")
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// maxMapCount default to slightly less than the typical
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// default on Linux (65K). We want to leave some
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// overhead for (e.g.) the Go runtime.
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var maxMapCount uint64 = 60000
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var mu sync.RWMutex
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func SetMaxMapCount(max uint64) {
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mu.Lock()
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maxMapCount = max
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mu.Unlock()
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}
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// Mmap increments the global map count, and then calls syscall.Mmap. It
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// decrements the map count and returns an error if the count was over the
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// limit. If syscall.Mmap returns an error it also decrements the count.
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func Mmap(fd int, offset int64, length int, prot int, flags int) (data []byte, err error) {
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mu.RLock()
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defer mu.RUnlock()
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if newCount := atomic.AddUint64(&mapCount, 1); newCount > maxMapCount {
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atomic.AddUint64(&mapCount, ^uint64(0)) // decrement
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return nil, ErrMaxMapCountReached
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}
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data, err = syscall.Mmap(fd, offset, length, prot, flags)
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if err != nil {
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atomic.AddUint64(&mapCount, ^uint64(0)) // decrement
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}
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return data, err
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}
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// Munmap calls sycall.Munmap, and then decrements the global map count if there
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// was no error.
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func Munmap(b []byte) (err error) {
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err = syscall.Munmap(b)
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if err == nil {
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atomic.AddUint64(&mapCount, ^uint64(0)) // decrement
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}
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return err
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}
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