Android Thread优先级和调度算法

Thread优先级设置方式：

java：

1. Process.setThreadPriority： android.os.Process.setThreadPriority(Process.THREAD_PRIORITY_LOWEST、Process.THREAD_PRIORITY_URGENT_AUDIO、-20)

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c++:

1. #include <sched.h>
2. setpriority(
3. https://blog.csdn.net/yangming2466/article/details/83280643

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Linux历程优先级系统——设置实时历程优先级_schedule里面priority 0-CSDN博客
Thread优先级原理（Android）

priority和nice关系：PR（NI+20）：将nice级别显示为映射到更大优先级队列，-20映射到0，+19映射到39

• main，renderthread 在app启动过程修改优先级源码：
  

if (curSchedGroup == ProcessList.SCHED_GROUP_TOP_APP) { // do nothing if we already switched to RT if (oldSchedGroup != ProcessList.SCHED_GROUP_TOP_APP) { app.getWindowProcessController().onTopProcChanged(); if (mService.mUseFifoUiScheduling) { // Switch UI pipeline for app to      SCHED_FIFO state.setSavedPriority(Process.getThreadPriority(app.getPid()));      mService.scheduleAsFifoPriority(app.getPid(), true); if (renderThreadTid != 0) {     mService.scheduleAsFifoPriority(renderThreadTid, /* suppressLogs */true);      if (DEBUG_OOM_ADJ) { Slog.d("UI_FIFO", "Set RenderThread (TID " + renderThreadTid + ") to FIFO"); } } else {     if (DEBUG_OOM_ADJ) { Slog.d("UI_FIFO", "Not setting RenderThread TID"); } } } else { // Boost priority for top app UI and render threads setThreadPriority(app.getPid(), THREAD_PRIORITY_TOP_APP_BOOST); if (renderThreadTid != 0) { try { setThreadPriority(renderThreadTid, THREAD_PRIORITY_TOP_APP_BOOST); } catch (IllegalArgumentException e) { // thread died, ignore } } } } } 恢复： else if (oldSchedGroup == ProcessList.SCHED_GROUP_TOP_APP && curSchedGroup != ProcessList.SCHED_GROUP_TOP_APP) { app.getWindowProcessController().onTopProcChanged(); if (mService.mUseFifoUiScheduling) { try {// Reset UI pipeline to SCHED_OTHER    setThreadScheduler(app.getPid(), SCHED_OTHER, 0);       setThreadPriority(app.getPid(), state.getSavedPriority()); if (renderThreadTid != 0) {   setThreadScheduler(renderThreadTid, SCHED_OTHER, 0); } } catch (IllegalArgumentException e) {   Slog.w(TAG, "Failed to set scheduling policy, thread does not exist:\n" + e); } catch (SecurityException e) {   Slog.w(TAG, "Failed to set scheduling policy, not allowed:\n" + e); } } else { // Reset priority for top app UI and render threads                setThreadPriority(app.getPid(), 0); } if (renderThreadTid != 0) {   setThreadPriority(renderThreadTid, THREAD_PRIORITY_DISPLAY); }

• 可控制不继承设置线程优先级：android.os.Process.setCanSelfBackground(false 作用是不让反面再有线程将优先级设置为background-level的举动,如有设置则直接抛出非常)
  

Scheduler 调度

调度算法分3大类：
SCHED_OTHER 默认调度计谋线程优先级100~120
SCHED_FIFO 线程优先级11~99
SCHED_RR
此中 RR+FIFO 是实时线程优先级，它们之间的区别是RR在相同优先级的线程之间会公平轮询，FIFO会独占CPU直到阻塞为止
修改方法：
Process.setThreadScheduler(tid, Process.SCHED_FIFO,1)
Process.setThreadScheduler(tid, Process.SCHED_RR | Process.SCHED_RESET_ON_FORK
说明：
不加Process.SCHED_RESET_ON_FORK，Process所有线程会被设置成RR
加上Process.SCHED_RESET_ON_FORK，指定线程会被设置成RR
Android的schedule包含4个cgroups：foreground，background，top-app，rt
线程绑定焦点实现方案：
Process.setThreadGroupAndCpuset(renderThreadTid, 8)
Android中cpuset包含5个cgroups：foreground，background，system-background，restricted，top-app

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