AMS-进程管理

进程调度：

进程优先级：没有发现一个和进程优先级直接挂钩的成员。但是应该跟一下内容有关：

* Android将应用进程分为五大类，分别是Foreground类，Visible类，Service类，

   Background类，Empty类。重要性是由高到低，应该算是进程优先级由高到低。

   这个可以作为进程调度优先级的依据，也可以作为OOM控制的依据。

* Process类中一些方法，如：

   /**
     * Sets the scheduling group for a process and all child threads
     * @hide
     * @param pid The identifier of the process to change.
     * @param group The target group for this process from THREAD_GROUP_*.
     *
     * @throws IllegalArgumentException Throws IllegalArgumentException if
     * <var>tid</var> does not exist.
     * @throws SecurityException Throws SecurityException if your process does
     * not have permission to modify the given thread, or to use the given
     * priority.
     *
     * group == THREAD_GROUP_DEFAULT means to move all non-background priority
     * threads to the foreground scheduling group, but to leave background
     * priority threads alone.  group == THREAD_GROUP_BG_NONINTERACTIVE moves all
     * threads, regardless of priority, to the background scheduling group.
     * group == THREAD_GROUP_FOREGROUND is not allowed.
     */

   setProcessGroup（int pid， int group）   对应ProcessRecord类中的setSchedGroup

   由注释可以知道该函数是用于设置进程属于那个组的，而只有两个组可以设置，就是

   THREAD_GROUP_DEFAULT和THREAD_GROUP_BG_NONINTERACTIVE，分别意

   味着将所有非后台优先级的线程都就移到到前台调度组，优先级为后台级别的线程

   则留下，和将所有线程不分优先级是否后台都移到后台调度组。而下面的setThreadGroup

  方法也是一样，指不过上面方法是对指定进程的所有线程进行操作，而下面的则是将指定的

   线程移到哪个组。移到不同的组的意义应该和调度有关。

   setThreadGroup（int tid， int group）    

   setThreadPriority（int priority）

* ActivityManagerService#mLruProcesses ： ArrayList<ProcessRecord>

   这是跟进程调度有关的一个数据结构，使用lru算法作为主要排序依据来对

   进程进行管理，应该是调度得越少的进程，会排越前面，更有机会被分配

   cpu资源。由ActivityManagerService#updateLurProcessInternalLocked（...）

   管理这个数据结构。

OOM控制：

在内存不足的情况下，杀掉oom优先级较低的进程，这个控制和进程调度是相对独立的。

* ProcessList类

   定义了不同状态下的进程的oom_adj值，值越小，越不容易被杀掉。

  下面是不同进程的oom_adj

   // Adjustment used in certain places where we don't know it yet.
    // (Generally this is something that is going to be cached, but we
    // don't know the exact value in the cached range to assign yet.)
    static final int UNKNOWN_ADJ = 16;

    // This is a process only hosting activities that are not visible,
    // so it can be killed without any disruption.
    static final int CACHED_APP_MAX_ADJ = 15;
    static final int CACHED_APP_MIN_ADJ = 9;

    // The B list of SERVICE_ADJ -- these are the old and decrepit
    // services that aren't as shiny and interesting as the ones in the A list.
    static final int SERVICE_B_ADJ = 8;

    // This is the process of the previous application that the user was in.
    // This process is kept above other things, because it is very common to
    // switch back to the previous app.  This is important both for recent
    // task switch (toggling between the two top recent apps) as well as normal
    // UI flow such as clicking on a URI in the e-mail app to view in the browser,
    // and then pressing back to return to e-mail.
    static final int PREVIOUS_APP_ADJ = 7;

    // This is a process holding the home application -- we want to try
    // avoiding killing it, even if it would normally be in the background,
    // because the user interacts with it so much.
    static final int HOME_APP_ADJ = 6;

    // This is a process holding an application service -- killing it will not
    // have much of an impact as far as the user is concerned.
    static final int SERVICE_ADJ = 5;//service类进程

    // This is a process with a heavy-weight application.  It is in the
    // background, but we want to try to avoid killing it.  Value set in
    // system/rootdir/init.rc on startup.
    static final int HEAVY_WEIGHT_APP_ADJ = 4;

    // This is a process currently hosting a backup operation.  Killing it
    // is not entirely fatal but is generally a bad idea.
    static final int BACKUP_APP_ADJ = 3;//正在执行backup操作的进程

    // This is a process only hosting components that are perceptible to the
    // user, and we really want to avoid killing them, but they are not
    // immediately visible. An example is background music playback.
    static final int PERCEPTIBLE_APP_ADJ = 2;

    // This is a process only hosting activities that are visible to the
    // user, so we'd prefer they don't disappear.
    static final int VISIBLE_APP_ADJ = 1;//visible类进程

    // This is the process running the current foreground app.  We'd really
    // rather not kill it!
    static final int FOREGROUND_APP_ADJ = 0;//foreground类进程

    // This is a process that the system or a persistent process has bound to,
    // and indicated it is important.
    static final int PERSISTENT_SERVICE_ADJ = -11;//这种类型的进程退出后

                                                                                           //系统需要重启，是重要进程
    // This is a system persistent process, such as telephony.  Definitely
    // don't want to kill it, but doing so is not completely fatal.
    static final int PERSISTENT_PROC_ADJ = -12;

    // The system process runs at the default adjustment.
    static final int SYSTEM_ADJ = -16;

    // Special code for native processes that are not being managed by the system (so
    // don't have an oom adj assigned by the system).
    static final int NATIVE_ADJ = -17;

* LKM

   是判断内存不足的标准，就是说他控制了杀掉进程的内存大小阀值。