Develop Reference

Is logging Android systrace events directly from native code possible, without JNI?

The Android systrace logging system is fantastic, but it only works in the Java portion of the code, through Trace.beginSection() and Trace.endSection(). In a C/C++ NDK (native) portion of the code it can only be used through JNI, which is slow or unavailable in threads without a Java environment...
Is there any way of either adding events to the main systrace trace buffer, or even generating a separate log, from native C code?
This older question mentions atrace/ftrace as being the internal system Android's systrace uses. Can this be tapped into (easily)?
BONUS TWIST: Since tracing calls would often be in performance-critical sections, it should ideally be possible to run the calls after the actual event time. i.e. I for one would prefer to be able to specify the times to log, instead of the calls polling for it themselves. But that would just be icing on the cake.

Posting a follow-up answer with some code, based on fadden's pointers. Please read his/her answer first for the overview.
All it takes is writing properly formatted strings to /sys/kernel/debug/tracing/trace_marker, which can be opened without problems. Below is some very minimal code based on the cutils header and C file. I preferred to re-implement it instead of pulling in any dependencies, so if you care a lot about correctness check the rigorous implementation there, and/or add your own extra checks and error-handling.
This was tested to work on Android 4.4.2.
The trace file must first be opened, saving the file descriptor in an atrace_marker_fd global:
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define ATRACE_MESSAGE_LEN 256
int atrace_marker_fd = -1;
void trace_init()
{
atrace_marker_fd = open("/sys/kernel/debug/tracing/trace_marker", O_WRONLY);
if (atrace_marker_fd == -1) { /* do error handling */ }
}
Normal 'nested' traces like the Java Trace.beginSection and Trace.endSection are obtained with:
inline void trace_begin(const char *name)
{
char buf[ATRACE_MESSAGE_LEN];
int len = snprintf(buf, ATRACE_MESSAGE_LEN, "B|%d|%s", getpid(), name);
write(atrace_marker_fd, buf, len);
}
inline void trace_end()
{
char c = 'E';
write(atrace_marker_fd, &c, 1);
}
Two more trace types are available, which are not accessible to Java as far as I know: trace counters and asynchronous traces.
Counters track the value of an integer and draw a little graph in the systrace HTML output. Very useful stuff:
inline void trace_counter(const char *name, const int value)
{
char buf[ATRACE_MESSAGE_LEN];
int len = snprintf(buf, ATRACE_MESSAGE_LEN, "C|%d|%s|%i", getpid(), name, value);
write(atrace_marker_fd, buf, len);
}
Asynchronous traces produce non-nested (i.e. simply overlapping) intervals. They show up as grey segments above the thin thread-state bar in the systrace HTML output. They take an extra 32-bit integer argument that "distinguishes simultaneous events". The same name and integer must be used when ending traces:
inline void trace_async_begin(const char *name, const int32_t cookie)
{
char buf[ATRACE_MESSAGE_LEN];
int len = snprintf(buf, ATRACE_MESSAGE_LEN, "S|%d|%s|%i", getpid(), name, cookie);
write(atrace_marker_fd, buf, len);
}
inline void trace_async_end(const char *name, const int32_t cookie)
{
char buf[ATRACE_MESSAGE_LEN];
int len = snprintf(buf, ATRACE_MESSAGE_LEN, "F|%d|%s|%i", getpid(), name, cookie);
write(atrace_marker_fd, buf, len);
}
Finally, there indeed seems to be no way of specifying times to log, short of recompiling Android, so this doesn't do anything for the "bonus twist".

I don't think it's exposed from the NDK.
If you look at the sources, you can see that the android.os.Trace class calls into native code to do the actual work. That code calls atrace_begin() and atrace_end(), which are declared in a header in the cutils library.
You may be able to use the atrace functions directly if you extract the headers from the full source tree and link against the internal libraries. However, you can see from the header that atrace_begin() is simply:
static inline void atrace_begin(uint64_t tag, const char* name)
{
if (CC_UNLIKELY(atrace_is_tag_enabled(tag))) {
char buf[ATRACE_MESSAGE_LENGTH];
size_t len;
len = snprintf(buf, ATRACE_MESSAGE_LENGTH, "B|%d|%s", getpid(), name);
write(atrace_marker_fd, buf, len);
}
}
Events are written directly to the trace file descriptor. (Note that the timestamp is not part of the event; that's added automatically.) You could do something similar in your code; see atrace_init_once() in the .c file to see how the file is opened.
Bear in mind that, unless atrace is published as part of the NDK, any code using it would be non-portable and likely to fail in past or future versions of Android. However, as systrace is a debugging tool and not something you'd actually want to ship enabled in an app, compatibility is probably not a concern.

For anybody googling this question in the future.
Native trace events are supported since API Level 23, check out the docs here https://developer.android.com/topic/performance/tracing/custom-events-native.

Automatically boot-up MTK devices (non-samsung) when docked

I'm developing a standalone kiosk using an android tablet(iBall running on 4.2.2).Its has the chinese MTK in it.
Suppose when there is no power,then eventually the tab's battery will drain out and have no juice left in it.When the power comes back I want the tab to automatically bootup without any manual intervention.I read online that if we modify the code present in the battery animation file we can achieve this.For the same,I replaced the original code of the battery charging animation file called 'ipod' located at '/system/bin' with :
#!/system/bin/sh
/system/bin/reboot
However,when my tab was shutdown and docked it didnt boot-up,instead it was just stuck at the charging logo.When I replaced the above code with:
/system/bin/reboot
my tab did boot-up when it was shutdown and docked.This means my code was getting stuck at '#!/system/bin/sh' . What could be the reason?
Also,while booting up the tab using the above process I want to boot it up after a delay,for which I used
sleep 20
/system/bin/reboot
but there was no delay in the bootup process(irrespective of the value of sleep that I give)
How do I create this delay ?
PS: I gave 777 permission to the file; owner-root; group-shell.
Kindly assist.Many thanks !

Found the reason my commands were not executing.
The reason was because,I was editing on my notepad++ on windows,until I came across this answer on SO -
" Make sure your text editor is not putting a /r /n and only a /n for every new line. This is typical if you are writing the script on windows.Use notepad++ (windows) and go to edit|EOL convention|UNIX then save it. "
So I changed my convention as per the above answer and ran my code and got the desired result.

I also had the need to make a device (alcatel9002x) autoboot on charger plugged, and come up with a solution replacing the ipod file. It runs the original ipod binary and at the same time, simulate pressing on the power button.
I see the charging animation, but after, it does a "normal" power up.
You probably can do this with a script but I did with with a .c binary.
Solution:
move /sbin/ipod to /sbin/ipod.backup
And use this code as the new binary /sbin/ipod
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dlfcn.h>
#include <unistd.h>
void run_cmd(char *s)
{
FILE *handle;
char buf[64];
size_t readn;
handle = popen(s, "r");
if (handle == NULL) {
return;
}
while ((readn = fread(buf, 1, sizeof(buf), handle)) > 0) {
fwrite(buf, 1, readn, stdout);
}
pclose(handle);
}
int main(void)
{
FILE *handle;
char buf[64];
size_t readn;
pid_t pid = fork();
if (pid == 0)
{
for(int i=0;i<10;i++)
{
run_cmd("/system/bin/sendevent /dev/input/event0 0001 116 1");
run_cmd("/system/bin/sendevent /dev/input/event0 0000 0000 00000000");
run_cmd("/system/bin/sleep 2");
run_cmd("/system/bin/sendevent /dev/input/event0 0001 116 00000000");
run_cmd("/system/bin/sendevent /dev/input/event0 0000 0000 00000000");
sleep(1);
}
}
else
{
run_cmd("/system/bin/sleep 2");
run_cmd("/system/bin/ipod.backup");
}
return 0;
}
I've compiled it with arm-linux-androideabi-gcc.
As I said, you probably can do this in a bash script, but this is how it worked for me.
Don't forget to chmod 667 and chown root:shell the binaries.

In Sony Xperia GO, the file name is "chargemon" and only by renaming it, the task is done (smartphone will be restart after plug in). (maybe other Sony brand smartphones be the same or similar)

Using time(NULL) on Android

Is there any known problem with using time(NULL) on Android?
I tried running the following piece of code:
int32_t now1 = time(NULL);
int64_t now1_6 = (int64_t)time(NULL);
int32_t nt = (time_t)-1;
int64_t nt6 = (int64_t)-1;
And then log the result using the following format:
"Now1 is %d. Now1_6 is %lld. NT is %d. NT6 is %lld.\n", now1, now1_6, nt, nt6
This is the output I got:
01-05 19:10:15.354: I/SMOS(11738): Now1 is 1533390320. Now1_6 is 6585861276402981128. NT is 0. NT6 is 283493768396.
There were other problems as well, such as getting the same time values on different loop iterations.
I encountered these issues on both a virtual and a physical device running Android 4.0.3 (API 15), both of which were configured with the correct time. The output above is from the physical device.
I am led to believe there is a problem with this particular POSIX function in Bionic, but I could not find any reference to such, either online or in the Bionic docs.

You are trying to cast an int64_t into a long long, and they might not be equivalent on Android. If you want to print out int64_t values using printf and %lld, either convert the number first to long long, or use the correct format modifier:
printf("%lld", (long long)now1_6);
or
printf("%" PRId64, now1_6);
For the time(NULL) giving false times, try using gettimeofday instead:
struct timeval tm;
gettimeofday( &tm, NULL);

Application is hanged after call nested function with Android NDK

I build Android project where I use Android NDK with LibXTract to extract audio features. LibXTract use fftw3 library. Project is consisted of button which runs simple example form libxtract:
JNIEXPORT void JNICALL Java_com_androidnative1_NativeClass_showText(JNIEnv *env, jclass clazz)
{
float mean = 0, vector[] = {.1, .2, .3, .4, -.5, -.4, -.3, -.2, -.1}, spectrum[10];
int n, N = 9;
float argf[4];
argf[0] = 8000.f;
argf[1] = XTRACT_MAGNITUDE_SPECTRUM;
argf[2] = 0.f;
argf[3] = 0.f;
xtract[XTRACT_MEAN]((void *)&vector, N, 0, (void *)&mean);
__android_log_print(ANDROID_LOG_DEBUG, "AndNat", "com_androidnative1_NativeClass.c before");
xtract_init_fft(N, XTRACT_SPECTRUM);
__android_log_print(ANDROID_LOG_DEBUG, "AndNat", "com_androidnative1_NativeClass.c after");
// Comment for test purpose
//xtract_init_bark(1, argf[1], 1);
//xtract[XTRACT_SPECTRUM]((void *)&vector, N, &argf[0], (void *)&spectrum[0]);
}
Libxtract function xtract_init_fft locate in jni/libxtract/jni/src/init.c execute fftw3 function fftwf_plan_r2r_1d located at jni/fftw3/jni/api/plan-r2r-1d.c
__android_log_print(ANDROID_LOG_DEBUG, "AndNat", "libxtract/src/init.c before");
fft_plans.spectrum_plan = fftwf_plan_r2r_1d(N, input, output, FFTW_R2HC, optimisation);
__android_log_print(ANDROID_LOG_DEBUG, "AndNat", "libxtract/src/init.c after");
Application hang inside fftwf_paln_r2r_1d without crash or any outher error I must force it to stop working.
fftwf_paln_r2r_1d looks like:
X(plan) X(plan_r2r_1d)(int n, R *in, R *out, X(r2r_kind) kind, unsigned flags)
{
__android_log_print(ANDROID_LOG_DEBUG, "AndNat", "fftw3/api/plan-r2r-1d.c");
return X(plan_r2r)(1, &n, in, out, &kind, flags);
}
From CatLog I can see:
07-16 18:50:09.615: D/AndNat(7313): com_androidnative1_NativeClass.c before
07-16 18:50:09.615: D/AndNat(7313): libxtract/src/init.c before
07-16 18:50:09.615: D/AndNat(7313): fftw3/api/plan-r2r-1d.c
I genereate config.h for fftw3 and libxtract with gen.sh scripts locate in source folder with success. Both librearies are build as static and linked with shared libary libcom_androidnative1_NativeClass.so
Command
nm -Ca libcom_androidnative1_NativeClass.so
shows that used function is included.
Application is built and deploys to device without any problems.
I build fftw3 with flags --disable-alloca, --enable-float and LibXTract with flags --enable-fft and --disable-dependency-tracking
Only ingerention in library source code was added dbgprint and remove define XTRACT_FFT form LibXtract beacouse it can't detect fftw library.
If somebody have any idea about this strange for me behavior please help.
Here I put entire project in github so maybe someone can help me handle this.
https://github.com/bl0ndynek/AndroidNative1

Thanks for FFTW3 maintainer problem is solved.
Solution was to change optimization level from FFTW_MEASURE to FFTW_ESTIMATE (from 1 to 0) in FFTW3,
FFTW's planner (in xtract_init_fft) actually executes and times different possible FFT algorithms in order to pick the fastest plan for a given n. In order to do this in as short a time as possible, however, the timer must have a very high resolution, and to accomplish this FFTW3 employ the hardware cycle counters that are available on most CPUs but not on Android default ARM configuration.
So this algorithm use gettimeofday() witch have low resolution and on ARM took forever on xtract_init_fft.

It looks to me like you are missing some terminating condition in your recursive function X() which would put you in an infinite loop.

printf, logcat and \n

I have C code that uses prints with something clever like
printf("hello ");
// do something
printf(" world!\n");
which outputs
hello world!
I want to reuse that code with Android and iOS, but Log.d() and NSLog() effectively add a newline at the end of every string I pass them, so that the output of this code:
NSLog(#"hello ");
// do something
NSLog(#"world!\n");
comes out (more or less) as:
hello
world!
I'm willing to replace printf with some macro to make Log.d and NSLog emulate printf's handling of '\n'; any suggestions?

One solution that might work is to define a global log function that doesn't flush its buffer until it finds a newline.
Here's a (very) simple version in java for android:
import java.lang.StringBuilder;
class CustomLogger {
private static final StringBuilder buffer = new StringBuilder();
public static void log(String message) {
buffer.append(message);
if(message.indexOf('\n') != -1) {
Log.d('SomeTag', buffer);
buffer.setLength(0);
}
}
}
...
CustomLogger.log("Hello, ");
// Stuff
CustomLogger.log("world!\n"); // Now the message gets logged
It's completely untested but you get the idea.
This particular script has some performance issues. It might be better to check if just the last character is a newline for example.
I just realized that you wanted this in C. It shouldn't be too hard to port though a standard lib wouldn't hurt (to get stuff like a string buffer).

For progeny, this is what I did: store logged strings in a buffer, and print the part before the newline whenever there is a newline in the buffer.

Yes, the NDK logcat is dumb about it. There are ways to redirect stderr/stdout to logcat, but there are drawbacks (either need to "adb shell setprop" which is only for rooted devices, or a dup() like technique but creating a thread just for that purpose is not a good idea on embedded devices IMHO though you can look further below for this technique).
So I did my own function/macros for that purpose. Here are snippets. In a debug.c, do this:
#include "debug.h"
#include <stdio.h>
#include <stdarg.h>
static const char LOG_TAG[] = "jni";
void android_log(android_LogPriority type, const char *fmt, ...)
{
static char buf[1024];
static char *bp = buf;
va_list vl;
va_start(vl, fmt);
int available = sizeof(buf) - (bp - buf);
int nout = vsnprintf(bp, available, fmt, vl);
if (nout >= available) {
__android_log_write(type, LOG_TAG, buf);
__android_log_write(ANDROID_LOG_WARN, LOG_TAG, "previous log line has been truncated!");
bp = buf;
} else {
char *lastCR = strrchr(bp, '\n');
bp += nout;
if (lastCR) {
*lastCR = '\0';
__android_log_write(type, LOG_TAG, buf);
char *rest = lastCR+1;
int len = bp - rest; // strlen(rest)
memmove(buf, rest, len+1); // no strcpy (may overlap)
bp = buf + len;
}
}
va_end(vl);
}
Then in debug.h do this:
#include <android/log.h>
void android_log(android_LogPriority type, const char *fmt, ...);
#define LOGI(...) android_log(ANDROID_LOG_INFO, __VA_ARGS__)
#define LOGW(...) android_log(ANDROID_LOG_WARN, __VA_ARGS__)
...
Now you just need to include debug.hpp and call LOGI() with a printf-like semantic buffered until a '\n' is encountered (or buffer is full).
This is not perfect though, as if the string generated from a call is longer than the buffer, it will be truncated and output. But frankly, 1024 chars should be enough in most cases (even less than this). Anyway, if this happens it will output a warning so you know about it.
Also note the vsnprintf() is not standard C (but it works in Android NDK). We could use vsprintf() instead (which is standard), but it is unsafe on its own.
======================================================================
Now for the dup() technique, you can look here (James Moore answer).
Then you can get rid of the function above and define your macro as:
#define LOG(...) fprintf(stderr, ...)
and you're done.
Advantages:
C/C++ libraries often use stderr for their logs. Using dup is the only way to have their output in logcat without modifying their code (some big ones use hundreds of direct calls to fprintf(stderr, ...))
stderr is standard C used since decades. All standard C library functions related to streams can be used with it. Same for C++, you can even use cerr with << operator. It works since under the hood, it still stderr.
Very long lines not truncated (instead, their are split). A good reason to use a shorter buffer (256 in the example).
Disadvantages:
A thread on its own (though it's an IO only thread, impact is close to nothing)
No log priority value (INFO, WARN, ERROR, etc...) can be choosen during the call. It uses a default one (INFO), so DMMS will always show stderr lines in the same color.

You could always just build the string one segment at a time:
String message = "Hello";
// Do Something
message += " World!";
Log.v("Example", message);