change native thread priority on Android in c/c++

Changing Native Thread Priority on Android

In Android, native threads (created using the POSIX threads library, pthread) can be assigned different priorities to influence their scheduling behavior. Higher-priority threads are more likely to receive CPU time, ensuring timely execution of critical tasks.

Understanding Thread Priorities

Thread priorities are represented as integers, with higher values denoting higher priority. The range of priorities varies based on the Android platform version, but generally, you can find the valid range through the constants ANDROID_PRIORITY_MIN and ANDROID_PRIORITY_MAX defined in android/os/Process.h.

Methods for Changing Thread Priority

Here are two common methods for changing native thread priority on Android in C/C++:

• android::Process::setThreadPriority(int priority)
• pthread_setschedparam(pthread_t thread, int policy, const struct sched_param *param)

android::Process::setThreadPriority

#include 

// ...
android::Process::setThreadPriority(android::Process::THREAD_PRIORITY_URGENT_DISPLAY);
// ...

This method takes a single argument: the desired priority. You can use the predefined constants from android/os/Process.h to specify priorities. Examples include:

• THREAD_PRIORITY_FOREGROUND: For threads performing visible UI updates.
• THREAD_PRIORITY_URGENT_DISPLAY: For critical UI rendering tasks.
• THREAD_PRIORITY_DEFAULT: The default priority for threads.
• THREAD_PRIORITY_BACKGROUND: For tasks that can be deferred or are not time-sensitive.

pthread_setschedparam

#include 
#include 

// ...
struct sched_param param;
param.sched_priority = 10; // Set desired priority
pthread_setschedparam(pthread_self(), SCHED_FIFO, ¶m);
// ...

This POSIX function offers more control over thread scheduling policies. Here’s a breakdown of the parameters:

• pthread_t thread: The thread handle.
• int policy: The scheduling policy. Common policies include SCHED_FIFO (First-In, First-Out) and SCHED_RR (Round-Robin).
• struct sched_param *param: A structure containing the scheduling parameters, including priority.

Comparison of Methods

Considerations

When changing thread priorities, keep in mind:

• Avoid excessive priority changes: Frequent changes can introduce performance overhead.
• Be mindful of potential deadlocks: A high-priority thread might block, preventing lower-priority threads from executing.
• Use thread priority judiciously: Prioritize only threads that require immediate or time-critical execution. Avoid unnecessarily boosting thread priorities.

Example

Here’s a simple example demonstrating changing the priority of a native thread using android::Process::setThreadPriority:

#include 
#include 
#include 

void *thread_function(void *arg) {
  while (true) {
    // Do some work
    printf("Thread running...\n");
    sleep(1);
  }
  return NULL;
}

int main() {
  pthread_t thread;
  int rc = pthread_create(&thread, NULL, thread_function, NULL);
  if (rc != 0) {
    printf("Error creating thread: %d\n", rc);
    return 1;
  }
  
  android::Process::setThreadPriority(android::Process::THREAD_PRIORITY_URGENT_DISPLAY);
  
  pthread_join(thread, NULL);
  return 0;
}

Thread running...
Thread running...
Thread running...
// ...