￭ Android 4.1/4.2/4.3 (Jelly Bean) Native Thread Scheduling Policy And Priority－Lexra Pixnet

Native Thread Scheduling Policy

...
#ifndef __CUTILS_SCHED_POLICY_H
#define __CUTILS_SCHED_POLICY_H

#ifdef __cplusplus
extern "C" {
#endif

/* Keep in sync with THREAD_GROUP_* in frameworks/base/core/java/android/os/Process.java */
typedef enum {
     SP_DEFAULT    = -1,
     SP_BACKGROUND = 0,
     SP_FOREGROUND = 1,
     SP_SYSTEM     = 2,  // can't be used with set_sched_policy()
     SP_AUDIO_APP  = 3,
     SP_AUDIO_SYS  = 4,
     SP_CNT,
     SP_MAX        = SP_CNT - 1,
     SP_SYSTEM_DEFAULT = SP_FOREGROUND,
 } SchedPolicy;
 
 /* Assign thread tid to the cgroup associated with the specified policy.
  * If the thread is a thread group leader, that is it's gettid() == getpid(),
  * then the other threads in the same thread group are _not_ affected.
  * On platforms which support gettid(), zero tid means current thread.
  * Return value: 0 for success, or -errno for error.
  */
extern int set_sched_policy(int tid, SchedPolicy policy);

/* Return the policy associated with the cgroup of thread tid via policy pointer.
* On platforms which support gettid(), zero tid means current thread.
* Return value: 0 for success, or -1 for error and set errno.
*/
extern int get_sched_policy(int tid, SchedPolicy *policy);

/* Return a displayable string corresponding to policy.
* Return value: non-NULL NUL-terminated name of unspecified length;
* the caller is responsible for displaying the useful part of the string.
*/
extern const char *get_sched_policy_name(SchedPolicy policy);

#ifdef __cplusplus
}
#endif

#endif /* __CUTILS_SCHED_POLICY_H */
...

Android Jelly Bean Scheduling Policy 包括:

SP_DEFAULT = -1,
SP_BACKGROUND = 0,
SP_FOREGROUND = 1,
SP_SYSTEM = 2, // can't be used with set_sched_policy()
SP_AUDIO_APP = 3,
SP_AUDIO_SYS = 4,
SP_CNT,
SP_MAX = SP_CNT - 1,
SP_SYSTEM_DEFAULT = SP_FOREGROUND,

請參考:

https://android.googlesource.com/platform/system/core/+/android-4.1.2_r2.1/include/cutils/sched_policy.h

Example of Set_sched_policy()

...
#include <cutils/sched_policy.h>
#include <cutils/properties.h>
...
set_sched_policy(androidGetTid(), SP_BACKGROUND);
...

Native Thread Scheduling Priority

#ifndef _LIBS_UTILS_THREAD_DEFS_H
#define _LIBS_UTILS_THREAD_DEFS_H
#include <stdint.h>
#include <sys/types.h>
#include <system/graphics.h>
// ---------------------------------------------------------------------------
// C API
#ifdef __cplusplus
extern "C" {
#endif
typedef void* android_thread_id_t;
typedef int (*android_thread_func_t)(void*);
enum {
    /*
     * ***********************************************
     * ** Keep in sync with android.os.Process.java **
     * ***********************************************
     * 
     * This maps directly to the "nice" priorities we use in Android.
     * A thread priority should be chosen inverse-proportionally to
     * the amount of work the thread is expected to do. The more work
     * a thread will do, the less favorable priority it should get so that 
     * it doesn't starve the system. Threads not behaving properly might
     * be "punished" by the kernel.
     * Use the levels below when appropriate. Intermediate values are
     * acceptable, preferably use the {MORE|LESS}_FAVORABLE constants below.
     */
    ANDROID_PRIORITY_LOWEST         =  19,
    /* use for background tasks */
    ANDROID_PRIORITY_BACKGROUND     =  10,
    
    /* most threads run at normal priority */
    ANDROID_PRIORITY_NORMAL         =   0,
    
    /* threads currently running a UI that the user is interacting with */
    ANDROID_PRIORITY_FOREGROUND     =  -2,
    /* the main UI thread has a slightly more favorable priority */
    ANDROID_PRIORITY_DISPLAY        =  -4,
    
    /* ui service treads might want to run at a urgent display (uncommon) */
    ANDROID_PRIORITY_URGENT_DISPLAY =  HAL_PRIORITY_URGENT_DISPLAY,
    
    /* all normal audio threads */
    ANDROID_PRIORITY_AUDIO          = -16,
    
    /* service audio threads (uncommon) */
    ANDROID_PRIORITY_URGENT_AUDIO   = -19,
    /* should never be used in practice. regular process might not 
     * be allowed to use this level */
    ANDROID_PRIORITY_HIGHEST        = -20,
    ANDROID_PRIORITY_DEFAULT        = ANDROID_PRIORITY_NORMAL,
    ANDROID_PRIORITY_MORE_FAVORABLE = -1,
    ANDROID_PRIORITY_LESS_FAVORABLE = +1,
};

請參考:

https://android.googlesource.com/platform/frameworks/native/+/jb-dev/include/utils/ThreadDefs.h

Example of Setpriority()

...
#include <cutils/sched_policy.h>
#include <cutils/properties.h>
...
    setpriority(PRIO_PROCESS, 0, ANDROID_PRIORITY_HIGHEST);
...

...
#ifdef HAVE_ANDROID_OS
int androidSetThreadPriority(pid_t tid, int pri) {
    int rc = 0;
    
#if defined(HAVE_PTHREADS)
    int lasterr = 0;
    pthread_once(&gDoSchedulingGroupOnce, checkDoSchedulingGroup);
    if (gDoSchedulingGroup) {
        // set_sched_policy does not support tid == 0
        int policy_tid;
        if (tid == 0) {
            policy_tid = androidGetTid();
        } else {
            policy_tid = tid;
        }
        if (pri >= ANDROID_PRIORITY_BACKGROUND) {
            rc = set_sched_policy(policy_tid, SP_BACKGROUND);
        } else if (getpriority(PRIO_PROCESS, tid) >= ANDROID_PRIORITY_BACKGROUND) {
            rc = set_sched_policy(policy_tid, SP_FOREGROUND);
        }
    }
    if (rc) {
        lasterr = errno;
    }
    if (setpriority(PRIO_PROCESS, tid, pri) < 0) {
        rc = INVALID_OPERATION;
    } else {
        errno = lasterr;
    }
#endif
    
    return rc;
}
int androidGetThreadPriority(pid_t tid) {
#if defined(HAVE_PTHREADS)
    return getpriority(PRIO_PROCESS, tid);
#else
    return ANDROID_PRIORITY_NORMAL;
#endif
}
#endif
...

請參考:

https://android.googlesource.com/platform/frameworks/native/+/jb-dev/libs/utils/Threads.cpp