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process_linux.go
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process_linux.go
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// Copyright (c) 2017 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
// Package process provides functions for inspecting processes.
package process
import (
"fmt"
"os"
"syscall"
"time"
)
const (
// syscallBatchSize controls the number of syscalls to perform before
// triggering a sleep.
syscallBatchSize = 10
defaultSyscallBatchDurationSleepMultiplier = 10
)
var (
dotBytes = []byte(".")
doubleDotBytes = []byte("..")
)
// numFDsSlow returns the number of file descriptors for a given process.
// This is a reference implementation that can be used to compare against for
// correctness.
func numFDsSlow(pid int) (int, error) {
statPath := fmt.Sprintf("/proc/%d/fd", pid)
d, err := os.Open(statPath)
if err != nil {
return 0, err
}
fnames, err := d.Readdirnames(-1)
d.Close()
return len(fnames), err
}
// NumFDs returns the number of file descriptors for a given process.
// This is an optimized implementation that avoids allocations as much as
// possible. In terms of wall-clock time it is not much faster than
// NumFDsReference due to the fact that the syscall overhead dominates,
// however, it produces significantly less garbage.
func NumFDs(pid int) (int, error) {
// Multiplier of zero means no throttling.
return NumFDsWithBatchSleep(pid, 0)
}
// NumFDsWithBatchSleep is the same as NumFDs but it throttles itself to prevent excessive
// CPU usages for processes with a lot of file descriptors.
//
// batchDurationSleepMultiplier is the multiplier by which the amount of time spent performing
// a single batch of syscalls will be multiplied by to determine the amount of time that the
// function will spend sleeping.
//
// For example, if performing syscallBatchSize syscalls takes 500 nanoseconds and
// batchDurationSleepMultiplier is 10 then the function will sleep for ~500 * 10 nanoseconds
// inbetween batches.
//
// In other words, a batchDurationSleepMultiplier will cause the function to take approximately
// 10x longer but require 10x less CPU utilization at any given moment in time.
func NumFDsWithBatchSleep(pid int, batchDurationSleepMultiplier float64) (int, error) {
statPath := fmt.Sprintf("/proc/%d/fd", pid)
d, err := os.Open(statPath)
if err != nil {
return 0, err
}
defer d.Close()
var (
b = make([]byte, 4096)
count = 0
lastSleep = time.Now()
)
for i := 0; ; i++ {
if i%syscallBatchSize == 0 && i != 0 {
// Throttle loop to prevent execssive CPU usage.
syscallBatchCompletionDuration := time.Now().Sub(lastSleep)
timeToSleep := time.Duration(float64(syscallBatchCompletionDuration) * batchDurationSleepMultiplier)
if timeToSleep > 0 {
time.Sleep(timeToSleep)
}
lastSleep = time.Now()
}
n, err := syscall.ReadDirent(int(d.Fd()), b)
if err != nil {
return 0, err
}
if n <= 0 {
break
}
_, numDirs := countDirent(b[:n])
count += numDirs
}
return count, nil
}
// NumFDsWithDefaultBatchSleep is the same as NumFDsWithBatchSleep except it uses the default value
// for the batchSleepDurationMultiplier.
func NumFDsWithDefaultBatchSleep(pid int) (int, error) {
return NumFDsWithBatchSleep(pid, defaultSyscallBatchDurationSleepMultiplier)
}