Define custom events for Systrace

Systrace shows you information about processes onlyat the system level, so it's sometimes difficult to know which of your app orgame's methods were executing at a given time relative to system events.

The Android platform provides a tracing API which you can use to label aparticular section of code. If you capture a new system trace of the "debug"version of your app and include the -a option, as shown in the followingsnippet, these custom events appear in a Systrace report:

python systrace.py -a com.example.myapp -b 16384 \
  -o my_systrace_report.html sched freq idle am wm gfx view binder_driver hal \
  dalvik camera input res

Note: This approach is different from using theDebug class, which helps you inspect detailedapp CPU usage by generating .trace files.

This guide describes how to define custom events in both managed code and nativecode.

Managed code

In Android 4.3 (API level 18) and higher, you can use theTrace class in your code to define customevents that then appear in Systrace reports, as shown in the following codesnippet.

Note: When you call beginSection() multiple times, calling endSection() ends only the most recently called beginSection() method. So, for nested calls, such as those in the following snippet, make sure that you properly match each call to beginSection() with a call to endSection().

Additionally, you cannot call beginSection() on one thread and end it from another thread; you must call both methods on the same thread.

Kotlin

class MyAdapter : RecyclerView.Adapter<MyViewHolder>() {
    override fun onCreateViewHolder(parent: ViewGroup,
            viewType: Int): MyViewHolder {
        return try {
            Trace.beginSection("MyAdapter.onCreateViewHolder")
            MyViewHolder.newInstance(parent)
        } finally {
            // In try and catch statements, always call "endSection()" in a
            // "finally" block. That way, the method is invoked even when an
            // exception occurs.
            Trace.endSection()
        }
    }
 
    override fun onBindViewHolder(holder: MyViewHolder, position: Int) {
        Trace.beginSection("MyAdapter.onBindViewHolder")
        try {
            try {
                Trace.beginSection("MyAdapter.queryDatabase")
                val rowItem = queryDatabase(position)
                dataset.add(rowItem)
            } finally {
                Trace.endSection()
            }
            holder.bind(dataset[position])
        } finally {
            Trace.endSection()
        }
    }
}

Java

public class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {
    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Trace.beginSection("MyAdapter.onCreateViewHolder");
        MyViewHolder myViewHolder;
        try {
            myViewHolder = MyViewHolder.newInstance(parent);
        } finally {
            // In try and catch statements, always call "endSection()" in a
            // "finally" block. That way, the method is invoked even when an
            // exception occurs.
            Trace.endSection();
        }
        return myViewHolder;
    }
 
   @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        Trace.beginSection("MyAdapter.onBindViewHolder");
        try {
            try {
                Trace.beginSection("MyAdapter.queryDatabase");
                RowItem rowItem = queryDatabase(position);
                dataset.add(rowItem);
            } finally {
                Trace.endSection();
            }
            holder.bind(dataset.get(position));
        } finally {
            Trace.endSection();
        }
    }
}

Native code

Android 6.0 (API level 23) and higher support a native tracing API, trace.h,to write trace events to the system buffer that you can then analyze usingSystrace. Common use cases for this API include observing the time that aparticular block of code takes to execute and associating a block of code withundesirable system behavior.

To define custom events that occur in the native code within your app or game,complete the following steps:

• Define function pointers for the ATrace functions that you use to capture custom events within your game, as shown in the following code snippet:

#include <android/trace.h>
#include <dlfcn.h>
 
void *(*ATrace_beginSection) (const char* sectionName);
void *(*ATrace_endSection) (void);
 
typedef void *(*fp_ATrace_beginSection) (const char* sectionName);
typedef void *(*fp_ATrace_endSection) (void);

• Load the ATrace symbols at runtime, as shown in the following code snippet. Usually, you perform this process in an object constructor.

// Retrieve a handle to libandroid.
void *lib = dlopen("libandroid.so", RTLD_NOW || RTLD_LOCAL);
 
// Access the native tracing functions.
if (lib != NULL) {
    // Use dlsym() to prevent crashes on devices running Android 5.1
    // (API level 22) or lower.
    ATrace_beginSection = reinterpret_cast<fp_ATrace_beginSection>(
        dlsym(lib, "ATrace_beginSection"));
    ATrace_endSEction = reinterpret_cast<fp_ATrace_endSection>(
        dlsym(lib, "ATrace_endSection"));
}

Caution: For security reasons, include calls to dlopen() only in the debug version of your app or game.

Note: To provide tracing support further back to Android 4.3 (API level 18), you can use JNI to call the methods in managed code around the code shown in the preceding snippet.

• Call ATrace_beginSection() and ATrace_endSection() at the beginning and end, respectively, of your custom event:

#include <android/trace.h>
 
char *customEventName = new char[32];
sprintf(customEventName, "User tapped %s button", buttonName);
 
ATrace_beginSection(customEventName);
// Your app or game's response to the button being pressed.
ATrace_endSection();

Note: When you call ATrace_beginSection() multiple times, calling ATrace_endSection() ends only the most recently called ATrace_beginSection() method. So, for nested calls, make sure that you properly match each call to ATrace_beginSection() with a call to ATrace_endSection().

Additionally, you cannot call ATrace_beginSection() on one thread and end it from another. You must call both functions from the same thread.

Convenience tips

The following tips are optional but might make it easier to analyze your nativecode.

Trace an entire function

When instrumenting your call stack or function timing, you might find it usefulto trace entire functions. You can use the ATRACE_CALL() macro to make thistype of tracing easier to set up. Furthermore, such a macro allows you to skipcreating try and catch blocks for cases where the traced function mightthrow an exception or call return early.

To create a macro for tracing an entire function, complete the following steps:

• Define the macro:

#define ATRACE_NAME(name) ScopedTrace ___tracer(name)
 
// ATRACE_CALL is an ATRACE_NAME that uses the current function name.
#define ATRACE_CALL() ATRACE_NAME(__FUNCTION__)
 
class ScopedTrace {
  public:
    inline ScopedTrace(const char *name) {
      ATrace_beginSection(name);
    }
 
    inline ~ScopedTrace() {
      ATrace_endSection();
    }
};

• Call the macro within the function that you want to trace:

void myExpensiveFunction() {
  ATRACE_CALL();
  // Code that you want to trace.
}

Name your threads

You can give a name to each thread in which your events occur, as demonstratedin the following code snippet. This step makes it easier to identify the threadsthat belong to specific actions within your game.

#include <pthread.h>
 
static void *render_scene(void *parm) {
    // Code for preparing your app or game's visual components.
}
 
static void *load_main_menu(void *parm) {
    // Code that executes your app or game's main logic.
}
 
void init_threads() {
    pthread_t render_thread, main_thread;
 
    pthread_create(&render_thread, NULL, render_scene, NULL);
    pthread_create(&main_thread, NULL, load_main_menu, NULL);
 
    pthread_setname_np(render_thread, "MyRenderer");
    pthread_setname_np(main_thread, "MyMainMenu");
}