前言
日常開發中,我們時常會聽到什麼IO密集型、CPU密集型任務...
那麼這裡提一個問題:大家知道什麼樣的任務或者代碼會被認定為IO/CPU密集?又是用什麼樣的標準來認定IO/CPU密集?
如果你沒有明確的答案,那麼就隨著這篇文章一起來聊一聊吧。
正文
最近團隊裡有基礎技術的同學對項目中的線程池進行了重新設計,調整了IO線程池等線程池的優化。因此藉助這個機會也就瞭解了一波開篇的那些問題。
一、宏觀概念區分
這一部分經驗豐富的同學都很熟悉。比如:
1.1、IO密集型任務
一般來說:文件讀寫、DB讀寫、網絡請求等
1.2、CPU密集型任務
一般來說:計算型代碼、Bitmap轉換、Gson轉換等
二、用代碼區分
上一part都是咱們憑藉經驗劃分的,這一part咱們就來用正經的指標來劃分任務。
先看有哪些數據指標可以用來進行評估(以下方法以系統日誌為準,加之開發經驗為輔):
1. wallTime
任務的整體運行時長(包括了running + runnable + sleep等所有時長)。獲取方案:
<code>run() { long start = System.currentTimeMillis(); // 業務代碼 long wallTime = System.currentTimeMillis() - start; }/<code>
2. cpuTime
cputime是任務真正在cpu上跑的時長,即為running時長
獲取方案1:
<code>run() { long start = SystemClock.currentThreadTimeMillis(); // 業務代碼 long cpuTime = SystemClock.currentThreadTimeMillis() - start; }/<code>
獲取方案2:
<code>/proc/pid/task/tid/schedse.sum_exec_runtime CPU上的運行時長/<code>
3. iowait time/count
指線程的iowait耗時。獲取方案:
<code>/proc/pid/task/tid/sched se.statistics.iowait_sum IO等待累計時間 se.statistics.iowait_count IO等待累計次數/<code>
具體日誌位置同上
4. runnable time
線程runnabel被調度的時長。獲取方案:
<code>/proc/pid/task/tid/sched se.statistics.wait_sum 就緒隊列等待累計時間/<code>
具體日誌位置同上
5. sleep time
線程阻塞時長(包括Interruptible-sleep和Uninterruptible-sleep和iowait的時長)。獲取方案:
<code>/proc/pid/task/tid/sched se.statistics.sum_sleep_runtime 阻塞累計時間/<code>
具體日誌位置同上
6. utime/stime
utime是線程在用戶態運行時長,stime是線程在內核態運行時長。獲取方案:
<code>/proc/pid/task/tid/stat 第14個字段是utime,第15個字段是stime/<code>
7. rchar/wchar
wchar是write和pwrite函數寫入的byte數。獲取方案:
<code>/proc/pid/task/tid/io rchar: ...wchar: .../<code>
(沒找到合適的日誌,暫不討論此情況)基於讀寫char數,我們可以將IO細分成讀IO密集型和寫IO密集型。
8. page_fault
缺頁中斷次數,分為major/minor fault。獲取方案:
<code>/proc/pid/task/tid/stat 第10個字段是minor_fault,第12個字段是major_fault/<code>
9. ctx_switches
線程在用戶/內核態的切換次數,分為voluntary和involuntary兩種切換。獲取方案:
<code>/proc/pid/task/tid/sched nr_switches 總共切換次數 nr_voluntary_switches 自願切換次數 nr_involuntary_switches 非自願切換次數/<code>
日誌位置同上
10. percpuload
平均每個cpu的執行時長。獲取方案:
<code>/proc/pid/task/tid/sched avg_per_cpu/<code>
日誌位置同上
有了上述這些指標,我們就可以開始我們的任務確定了。
以下內容,大家可以自行測試加深印象。
2.1、IO密集型任務
比如這段代碼:
<code>val br = BufferedReader(FileReader("xxxx"), 1024) try { while (br.readLine() != null) { } } finally { if (br != null) { br.close() } }/<code>
基於上述部分3. iowait time/count,我們可以在對應的日誌文件中看出這段代碼有明顯的iowait 。
2.2、CPU密集型任務
比如這段代碼:
<code>var n = 0.0 for (i in 0..9999999) { n = Math.cos(i.toDouble() )}/<code>
基於上述部分6. utime/stime的內容,看一看出這段代碼utime會佔比非常高,且幾乎沒有stime,此外沒有io相關的耗時。
三、這玩意有啥用?
說白了,我們一切的優化手段都是為了服務於業務。對於業務開發來說:
為了不佔用主線程 -> 所以啟一個新線程 -> 頻繁的new線程又會帶來大量的開銷 -> 所以使用線程池進行復用 -> 而不合理的線程池設計又會帶來線程使用低效,甚至新加入的任務只能等待 -> 優化線程池
舉個最簡單的例子:線程池中放了最大允許倆個線程並行,那麼假設運行中的倆個都是長IO的任務。那麼新來的任務就只能等,哪怕它並不是特別耗時...
因此這玩意有啥用,還不是為更好的線程池設計做指導思想,更好的提升線程運行效率,降低業務上不必要的等待。
這裡提供一些可供參考的工具方法和線程池設計:
3.1、判斷任務類型
這裡貼一些核心的思路,畢竟全部方案數據公司的代碼,我也不方便全部貼出來:
<code>class TaskInfo { var cpuTimeStamp = 0.0 var timeStamp = 0.0 var iowaitTime = 0.0 var sleepTime = 0.0 var runnableTime = 0.0 var totalSwitches = 0.0 var voluntarySwitches = 0.0}/<code>
<code>object TaskInfoUtils { private const val SUM_SLEEP_RUNTIME = "se.statistics.sum_sleep_runtime" private const val WAIT_SUM = "se.statistics.wait_sum" private const val IOWAIT_SUM = "se.statistics.iowait_sum" private const val NR_SWITCHES = "nr_switches " private const val NR_VOLUNTARY_SWITCHES = "nr_voluntary_switches" private var schedPath = ThreadLocal() fun buildCurTaskInfo(): TaskInfo { val threadInfo = TaskInfo() threadInfo.timeStamp = System.currentTimeMillis().toDouble() threadInfo.cpuTimeStamp = SystemClock.currentThreadTimeMillis().toDouble() if (schedPath.get() == null) { schedPath.set("/proc/${android.os.Process.myPid()}/task/${getTid()}/sched") } BufferedReader(FileReader(schedPath.get()), READ_BUFFER_SIZE).use { br -> br.readLines().forEach { line -> when { line.startsWith(SUM_SLEEP_RUNTIME) -> threadInfo.sleepTime = line.split(":")[1].toDouble() line.startsWith(WAIT_SUM) -> threadInfo.runnableTime = line.split(":")[1].toDouble() line.startsWith(IOWAIT_SUM) -> threadInfo.iowaitTime = line.split(":")[1].toDouble() line.startsWith(NR_SWITCHES) -> threadInfo.totalSwitches = line.split(":")[1].toDouble() line.startsWith(NR_VOLUNTARY_SWITCHES) -> threadInfo.voluntarySwitches = line.split(":")[1].toDouble() } } } return threadInfo }}/<code>
<code>object TaskBoundJudge { private const val CPU_CPUTIME_INTERVAL = 0.8 private const val CPU_SWITCHES_INTERVAL = 0.1 private const val CPU_IOWAIT_INTERVAL = 0.01 private const val CPU_SLEEP_INTERVAL = 0.02 private const val CPU_CPUTIME_WEIGHTS = 0.1 private const val CPU_SWITCHES_WEIGHTS = 0.35 private const val CPU_IOWAIT_WEIGHTS = 0.15 private const val CPU_SLEEP_WEIGHTS = 0.40 private const val IO_CPUTIME_INTERVAL = 0.5 private const val IO_SWITCHES_INTERVAL = 0.4 private const val IO_IOWAIT_INTERVAL = 0.1 private const val IO_SLEEP_INTERVAL = 0.15 private const val IO_CPUTIME_WEIGHTS = 0.1 private const val IO_SWITCHES_WEIGHTS = 0.35 private const val IO_IOWAIT_WEIGHTS = 0.35 private const val IO_SLEEP_WEIGHTS = 0.2 fun isCpuTask(start: TaskInfo?, end: TaskInfo?): Boolean { if (start == null || end == null) { return false } val wallTime = end.timeStamp - start.timeStamp val cpuTime = end.cpuTimeStamp - start.cpuTimeStamp val runnableTime = end.runnableTime - start.runnableTime val totalSwitches = end.totalSwitches - start.totalSwitches val voluntarySwitches = end.voluntarySwitches - start.voluntarySwitches val iowaitTime = end.iowaitTime - start.iowaitTime val sleepTime = end.sleepTime - start.sleepTime var result = 0.0 if (cpuTime / (wallTime - runnableTime) > CPU_CPUTIME_INTERVAL) { result += CPU_CPUTIME_WEIGHTS } if (voluntarySwitches / totalSwitches < CPU_SWITCHES_INTERVAL) { result += CPU_SWITCHES_WEIGHTS } if (iowaitTime / sleepTime < CPU_IOWAIT_INTERVAL) { result += CPU_IOWAIT_WEIGHTS } if (sleepTime / (wallTime - runnableTime) < CPU_SLEEP_INTERVAL) { result += CPU_SLEEP_WEIGHTS } return result > 0.5 } fun isIOTask(start: TaskInfo?, end: TaskInfo?): Boolean { if (start == null || end == null) { return false } val wallTime = end.timeStamp - start.timeStamp val cpuTime = end.cpuTimeStamp - start.cpuTimeStamp val runnableTime = end.runnableTime - start.runnableTime val totalSwitches = end.totalSwitches - start.totalSwitches val voluntarySwitches = end.voluntarySwitches - start.voluntarySwitches val iowaitTime = end.iowaitTime - start.iowaitTime val sleepTime = end.sleepTime - start.sleepTime var result = 0.0 if (cpuTime / (wallTime - runnableTime) < IO_CPUTIME_INTERVAL) { result += IO_CPUTIME_WEIGHTS } if (voluntarySwitches / totalSwitches > IO_SWITCHES_INTERVAL) { result += IO_SWITCHES_WEIGHTS } if (iowaitTime / sleepTime > IO_IOWAIT_INTERVAL) { result += IO_IOWAIT_WEIGHTS } if (sleepTime / (wallTime - runnableTime) > IO_SLEEP_INTERVAL) { result += IO_SLEEP_WEIGHTS } return result > 0.5 } }/<code>
當我們想對某個方法進行計算是CPU還是IO。可以在這個方法的開始、結束調用 TaskInfoUtils.buildCurTaskInfo();然後調用 TaskBoundJudge.isCpuTask(start,end), TaskBoundJudge.isIOTask(start,end)即可。
3.2、線程池
IO密集型參考線程池:
<code>public static final ExecutorService IO_EXECUTOR = new ThreadPoolExecutor( 2, 128, 15, TimeUnit.SECONDS, new SynchronousQueue<>(), new CustomThreadFactory("MDove-IO", CustomThreadPriority.NORMAL), AbortPolicy() // 根據業務情況,自行定義拒絕實現。比如上報監控平臺 );/<code>
CPU密集型參考線程池:
<code>public static final int CPU_COUNT = Runtime.getRuntime().availableProcessors(); public static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1; private static final int CPU_CORE_POOL_SIZE = Math.max(Math.min(MAXIMUM_POOL_SIZE, 4), Math.min(CPU_COUNT + 1, 9)); public static final ExecutorService CPU_EXECUTOR = new ThreadPoolExecutor( CPU_CORE_POOL_SIZE, CPU_COUNT * 2 + 1, 30, TimeUnit.SECONDS, new LinkedBlockingQueue<>(256), new SSThreadFactory("MDove-CPU", CustomThreadPriority.NORMAL), AbortPolicy() // 根據業務情況,自行定義拒絕實現。比如上報監控平臺 );/<code>
上述線程池中設計的額外代碼:
<code>class CustomThreadFactory : ThreadFactory { var name: String private set private var priority = CustomThreadPriority.NORMAL constructor(name: String, priority: CustomThreadPriority) { this.name = name this.priority = priority } override fun newThread(r: Runnable): Thread { val name = name + "-" + sCount.incrementAndGet() return object : Thread(r, name) { override fun run() { if (priority == CustomThreadPriority.LOW) { Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND) } else if (priority == CustomThreadPriority.HIGH) { Process.setThreadPriority(Process.THREAD_PRIORITY_DISPLAY) } super.run() } } } companion object { private val sCount = AtomicInteger(0) } } enum class CustomThreadPriority { LOW, NORMAL, HIGH, IMMEDIATE }/<code>
尾聲
OK,這篇文章到這裡就結束了。希望這篇文章能給大家在線程的使用和線程池的設計上帶來幫助。
最後,讓我們一起加油吧,“打工人”!