I am storing off JNIEnv in a global so I can call static java methods later. But is it nessasary to store off a global pointer to the JNIEnv, they way one would with any other java object, or is it a special case that does not require this.
JNIEnv* globalEnvPointer;
[JNICALL etc] void init(JNIENv* env, [etc])
{
//required?
globalEnvPointer = (JNIENv*) (env*)->GetGlobalRef(env, env);
//or is this OK?
globalEnvPointer = env;
}
Edit
I'm bing a bit dumb here, all the methods that will use globalEnvPointer, are invoked within my init because my init is actually my c program's main method, which won't return until the end of the program. I am also using no other threads in the c program. I think this simplifies the answer.
JNIEnv* globalEnvPointer;
[JNICALL etc] void main(JNIENv* env, [etc])
{
//required?
globalEnvPointer = (JNIENv*) (env*)->GetGlobalRef(env, env);
//or is this OK?
globalEnvPointer = env;
someMethod();
}
void someMethod()
{
//use globalEnvPointer here
}
You cannot cache the JNIEnv pointer. Read about it here:
The JNI interface pointer (JNIEnv) is valid only in the current thread. Should another thread need to access the Java VM, it must first call AttachCurrentThread() to attach itself to the VM and obtain a JNI interface pointer. Once attached to the VM, a native thread works just like an ordinary Java thread running inside a native method. The native thread remains attached to the VM until it calls DetachCurrentThread() to detach itself.
What you can do is to cache the JavaVM pointer instead.
static JavaVM *jvm;
[JNICALL etc] void init(JNIENv* env, [etc])
{
jint rs = (*env)->GetJavaVM(env, &jvm);
assert (rs == JNI_OK);
}
And then whenever you need then JNIEnv pointer from a context where it is not given you do this:
void someCallback() {
JNIEnv *env;
jint rs = (*jvm)->AttachCurrentThread(jvm, &env, NULL);
assert (rs == JNI_OK);
// Use the env pointer...
}
But whenever you call a native method from Java the env pointer to use is given:
JNIEXPORT jint JNICALL Java_package_Class_method(JNIEnv *env, jobject obj) {
// just use the env pointer as is.
}
Related
When porting from NAOqi to qi framework I achieved a partial success. I do however still have the following problem.
I do not know how to implement sound processing with ALSoundExtractor in qi framework.
In old Naoqi, there is an example:
http://doc.aldebaran.com/2-8/dev/cpp/examples/audio/soundprocessing/soundprocessing.html
where a class is created:
class ALSoundProcessing : public ALSoundExtractor
then a function overriding a virtual function is declared, one that is used for sound processing:
void process(...)
What I don't now is:
How to create a class in qi framework that inherits from the old style class ALSoundExtractor?
How to declare a function that is overriding the virtual function - technically the base class function process() expects variables in old AL:: convention.
Alternatively, is there any other way to read the audio channels?
I never worked with ALExtractor nor ALSoundExtractor, but here is what I know.
How to create a class in qi framework that inherits from the old style class ALSoundExtractor?
in the old Naoqi, an "ALExtractor"
could run either from within the main process (using autoload.ini) or from another one (known as remote mode). With the qi framework, only the remote mode is supported.
could inherit from ALExtractor or ALAudioExtractor to get some code factored out. Those classes have not been ported to the qi framework. So if you don't want to keep using libnaoqi, you should find a way to do without them.
Good news: inheriting from them never was really needed. You'll find yourself in a similar position as in the following question where an extractor is implemented in python (and thus cannot inherit from a C++ class, nor be loaded in the main process from autoload.ini).
NAO robot remote audio problems
How to declare a function that is overriding the virtual function - technically the base class function process() expects variables in old AL:: convention.
Whenever you use the "old Naoqi" you're actually using a compatibility layer on top of the qi framework.
So whenever you use the "old Naoqi", you're already using the qi framework.
libqi's qi::AnyValue is extensible at runtime, libnaoqi extends it to let it know how to handle an ALValue: how to convert it into primitive types (floating point number, list of ints, string, buffer, etc.).
So whenever an old ALSoundExtractor receives an AL::ALvalue, it is actually a qi::AnyValue which has been converted into an ALValue just before calling the process() method.
If you don't link with libnaoqi, you won't be able to use the value as an ALValue, but you can use it as a qi::AnyValue or even use it as a primitive type.
The original prototype is (cfr doxygen http://doc.aldebaran.com/2-8/ref/libalaudio/classAL_1_1ALSoundExtractor.html) is
void ALSoundExtractor::process (const int &nbOfChannels, const int &nbrOfSamplesByChannel, const AL_SOUND_FORMAT *buffer, const ALValue ×tamp);
Since timestamp is probably a list of two ints, I would try something like this
void TmpSoundExtractor::process (const int &nbOfChannels, const int &nbrOfSamplesByChannel, qi::AnyValue buffer, const std::vector<int> ×tamp);
I'm not sure how to handle the buffer variable, but let first get the rest working.
To use this API, you must write a Qi Service that advertises this method:
void processRemote(
int nbOfChannels,
int nbrOfSamplesByChannel,
const qi::AnyValue& timestamp,
const qi::AnyValue& buffer)
{
std::pair<char*, size_t> charBuffer = value.unwrap().asRaw();
const signed short* data = (const signed short*)charBuffer.first;
// process the data like in the example.
}
Note that with the Qi framework:
AL::ALValue is replaced by qi::AnyValue.
Getting the binary data (aka "raw") is slightly different.
AL_SOUND_FORMAT is replaced by signed short*.
ALSoundExtractor is not available, so we needed to do the conversion to const AL_SOUND_FORMAT* by ourselves.
Say your service is registered as "MySoundExtractor", you will have to tell ALAudioDevice to start the sound extraction and send the data to your service as follows:
auto audio = session->service("ALAudioDevice").value();
int nNbrChannelFlag = 0; // ALL_Channels: 0, AL::LEFTCHANNEL: 1, AL::RIGHTCHANNEL: 2; AL::FRONTCHANNEL: 3 or AL::REARCHANNEL: 4.
int nDeinterleave = 0;
int nSampleRate = 48000;
audio->setClientPreferences("MySoundExtractor", nSampleRate, nNbrChannelFlag, nDeinterleave);
audio->subscribe("MySoundExtractor");
Note that I did not test this code, so let me know what may be wrong.
The following is what has eventually worked for me and concludes the topic.
// **************** service.h ****************
typedef signed short AL_SOUND_FORMAT; // copy from alaudio/alsoundextractor.h
class SoundProcessing
{
public:
SoundProcessing(qi::SessionPtr session);
void init(void); // a replacement for a function automatically called in NAOqi 2.1.4
virtual ~SoundProcessing(void);
void processRemote(const int& nbOfChannels, const int& nbrOfSamplesByChannel, const qi::AnyValue& timestamp, const qi::AnyValue& buffer);
private:
qi::SessionPtr _session;
qi::AnyObject audio;
};
// **************** service.cpp ****************
SoundProcessing::SoundProcessing(qi::SessionPtr session) : _session(session)
{
_session->waitForService("ALAudioDevice");
audio = _session->service("ALAudioDevice");
} // constructor
QI_REGISTER_MT_OBJECT(SoundProcessing, init, processRemote);
SoundProcessing::~SoundProcessing(void)
{
audio.call<qi::AnyValue>("unsubscribe", "SoundProcessing");
} // destructor
void SoundProcessing::init(void)
{
audio.call<qi::AnyValue>("setClientPreferences",
"SoundProcessing",
_FREQ48K, // 48000 Hz requested
0,
1
);
audio.call<qi::AnyValue>("subscribe", "SoundProcessing");
} // SoundProcessing::init
void SoundProcessing::processRemote(const int& nbOfChannels,const int& nbrOfSamplesByChannel, const qi::AnyValue& timestamp, const qi::AnyValue& qibuffer)
{
std::pair<char*, size_t> charBuffer = qibuffer.unwrap().asRaw();
AL_SOUND_FORMAT *buffer = (AL_SOUND_FORMAT *)charBuffer.first;
(...)
} // SoundProcessing::process
// **************** main.cpp ****************
int main(int argc, char* argv[])
{
qi::ApplicationSession app(argc, argv);
app.start();
qi::SessionPtr session = app.session();
session->registerService("SoundProcessing", qi::AnyObject(boost::make_shared<SoundProcessing>(session)));
qi::AnyObject sp = session->service("SoundProcessing");
sp.call<qi::AnyValue>("init");
app.run();
return 0;
}
The following is what I did. The code compiles, but I won't have a chance to test it on a live robot for about one week or so.
typedef signed short AL_SOUND_FORMAT; // copy from alaudio/alsoundextractor.h
void process(const int& nbOfChannels, const int& nbrOfSamplesByChannel, const AL_SOUND_FORMAT *buffer, const qi::AnyValue& timeStamp); // I do not use the timeStamp variable in my code, so AnyValue would work?
qi::AnyObject audioDevice = _session->service("ALAudioDevice"); // same variable name as in the original ALSoundExtractor module, just as a convenience
audioDevice.call<qi::AnyValue>("setClientPreferences", audioDevice.call<qi::AnyValue>("getName"), 48000, 0, 1);
audioDevice.call<qi::AnyValue>("subscribe", audioDevice.call<qi::AnyValue>("getName")); // this is the key call
audioDevice.call<qi::AnyValue>("startDetection"); // is it still necessary?
My question is - do I do it right now? If I cannot override the virtual function process(), does subscribing of my module guarantee a callback to my process(...)?
I am trying to wrap a library for porting purpose. The library exposes a function say -
fooLib(int , char , function pointer A);
signature of the function pointer A is
void handler(DataFormat);
where DataFormat is a struct
I don't want my wrapper to expose this library's callback function. I want to create a different function that should be used by the consumers of my wrapper, say
int handlerNew(NewDataFormat);
where NewDataFormat is my struct
The question now is how can I link these two functions? Whenever the library calls handler I want it to call my callback handlerNew after filling up the NewDataFormat struct from the DataFormat.
As long as you don't need thread safety, this is not hard. You just have to provide a private (static) handler with the library's interface that transforms the library data struct into your wrapped version, then calls your callback with that as an argument. Your interface will look like:
// wrapped_foo_lib.h
typedef struct { ... } NewDataFormat;
typedef void (*WRAPPED_CALLBACK)(NewDataFormat);
void wrappedFooLibCall(int x, char c, WRAPPED_CALLBACK cb);
Your implementation, which the client never gets to see is:
// wrapped_foo_lib.c
// This static var makes this module _not_ thread safe.
static WRAPPED_CALLBACK wrapped_callback;
static void private_handler(DataFormat data) {
NewDataFormat new_data = ...; // extract new_data from data
wrapped_callback(new_data);
}
void wrappedFooLibCall(int x, char c, WRAPPED_CALLBACK cb) {
wrapped_callback = cb;
foo_lib(x, c, private_handler);
}
The non-thread safety is why every API callback should include a void * that you get to define, which is passed on to the callback. I.e. your furnished library should be defined as
fooLib(int, char, void (*)(DataFormat, void *env));
void handler(DataFormat, void *env);
Now when you call fooLib, you furnish any struct at all as env, and it's passed back to you. This way you can dispense with the static variable in the wrapper:
// wrapped_foo_lib.c
typedef struct { WRAPPED_CALLBACK wrapped_callback; } ENV;
static void private_handler(DataFormat data, void *void_env) {
ENV *env = (ENV*)void_env;
NewDataFormat new_data = ...; // extract new_data from data
env->wrapped_callback(new_data);
}
void wrappedFooLibCall(int x, char c, WRAPPED_CALLBACK cb) {
ENV env[1] = {{ cb }};
foo_lib(x, c, env);
}
This is thread safe because ENV is stack allocated. A nice example of this done well is the libpng.
Feel free to update the C90 to more modern syntax.
How do I pass a delegate to an external C function taking a function pointer, in D?
Let me cross post what I said on the newsgroup:
How do I pass a delegate to an external C function taking a
function pointer?
You can't do it directly in general, unless you can modify the C
function, then you can hack around it, but a delegate and a
regular function pointer are pretty different animals.
But perhaps you can magic hack it. Observe:
// a C function that needs a plain function
extern(C) void test(void function() f) {
// pretend this is implemented in C
f();
}
// just create a random delegate
void delegate() foo(int a) {
return { import std.stdio; writeln(a); };
}
// what we want to work
void main() {
auto dg = foo(10);
dg(); // works
//test(dg); // won't work
test(bindDelegate(dg)); // we want this
}
// transform delegate into pointer..
import std.traits;
auto bindDelegate(T, string file = __FILE__, size_t line = __LINE__)(T t) if(isDelegate!T) {
static T dg;
dg = t;
extern(C)
static ReturnType!T func(ParameterTypeTuple!T args) {
return dg(args);
}
return &func;
}
What bindDelegate does is create a special static variable and
function for that specific call. It is as if we wrote a separate
function and global to hold it.
The __FILE__, __LINE__ things are a filthy hack to make it
instantiate a separate variable+function pair for different
lines so the global variable holding the delegate won't be so
easily overwritten.
I have followed the advice at
registering java function as a callback in C function and can callback with "simple" types such as integer and string, e.g.:
jstring js = (*env)->NewStringUTF(env, "hello");
(*env)->CallStaticVoidMethod(env, cls, methodid, js);
However, if I am trying to do the same with C datatypes which have been wrapped with SWIG, I am only getting null pointers in Java. In the C part they are definitely not 0. Do they need to be treated differently?
[EDIT:]
Some more information:
As stated above, char*/string is working for me as well. I am looking for a solution for C struct's, which have been wrapped by SWIG and have been allocated in Java.
E.g.:
typedef struct {
unsigned short length;
unsigned short value;
} lv_t;
is getting wrapped by SWIG, so I can use it in Java:
lv_t lv;
lv = modulename.modulename_new_lv();
lv.setLength(1);
lv.setValue(2);
Then I will give this struct from Java to C:
modulename.send(lv);
C will send it over the network, receive some reply and change the values in lv. Now, this should give the modified lv back to Java.
void jni_call_received_hook(lv_t* lv){
JNIEnv* m_env;
(*m_vm)->AttachCurrentThread(m_vm, (void**) &m_env, NULL );
jclass cls = (*m_env)->FindClass( m_env, "gui/StateMachine" );
jmethodID mid = (*m_env)->GetStaticMethodID(m_env, cls, "callReceivedEvent", "(Lcom/something/modulename/jni/lv_t;)V");
if (mid == 0){
log(E, "Unable to find method for callback");
return;
}
// what to do here to create a jobject?
jobject lv_j = ...;
(*m_env)->CallStaticVoidMethod(m_env, cls, mid, lv_j);
}
Which calls:
public static void messageHandler(lv_t lv) {
System.out.println("messageHandler().");
System.out.println("lv " + lv);
}
Sorry but I'm not able to comment in your question yet, so this is more a comment rather than an answer. Anyway, I've recently done something like that.
My callback works and is implemented as:
void jni_call_received_hook(char* username){
JNIEnv* m_env;
(*m_vm)->AttachCurrentThread(m_vm, (void**) &m_env, NULL );
jclass cls = (*m_env)->FindClass( m_env, "gui/StateMachine" );
jmethodID mid = (*m_env)->GetStaticMethodID(m_env, cls, "callReceivedEvent", "(Ljava/lang/String;)V");
if (mid == 0){
log(E, "Unable to find method for callback");
return;
}
(*m_env)->CallStaticVoidMethod(m_env, cls, mid, (*m_env)->NewStringUTF(m_env, username));
}
The variable m_vm is an instance of the JVM I've kept upon calling a method that registered this callback, like this:
JNIEXPORT void JNICALL Java_gui_StateMachine_setCallReceivedCallback(JNIEnv *e, jobject o){
(*e)->GetJavaVM(e, &m_vm );
set_call_received_hook(jni_call_received_hook);
}
Maybe your missing something. Let me know if this isn't clear enough. Hope it helps.
What's the best way to create a singleton in C? A concurrent solution would be nice.
I am aware that C isn't the first language you would use for a singleton.
First, C is not suitable for OO programming. You'd be fighting all the way if you do. Secondly, singletons are just static variables with some encapsulation. So you can use a static global variable. However, global variables typically have far too many ills associated with them. You could otherwise use a function local static variable, like this:
int *SingletonInt() {
static int instance = 42;
return &instance;
}
or a smarter macro:
#define SINGLETON(t, inst, init) t* Singleton_##t() { \
static t inst = init; \
return &inst; \
}
#include <stdio.h>
/* actual definition */
SINGLETON(float, finst, 4.2);
int main() {
printf("%f\n", *(Singleton_float()));
return 0;
}
And finally, remember, that singletons are mostly abused. It is difficult to get them right, especially under multi-threaded environments...
You don't need to. C already has global variables, so you don't need a work-around to simulate them.
It's the same as the C++ version pretty much. Just have a function that returns an instance pointer. It can be a static variable inside the function. Wrap the function body with a critical section or pthread mutex, depending on platform.
#include <stdlib.h>
struct A
{
int a;
int b;
};
struct A* getObject()
{
static struct A *instance = NULL;
// do lock here
if(instance == NULL)
{
instance = malloc(sizeof(*instance));
instance->a = 1;
instance->b = 2;
}
// do unlock
return instance;
};
Note that you'd need a function to free up the singleton too. Especially if it grabs any system resources that aren't automatically released on process exit.
EDIT: My answer presumes the singleton you are creating is somewhat complex and has a multi-step creation process. If it's just static data, go with a global like others have suggested.
A singleton in C will be very weird . . . I've never seen an example of "object oriented C" that looked particularly elegant. If possible, consider using C++. C++ allows you to pick and choose which features you want to use, and many people just use it as a "better C".
Below is a pretty typical pattern for lock-free one-time initialization. The InterlockCompareExchangePtr atomically swaps in the new value if the previous is null. This protects if multiple threads try to create the singleton at the same time, only one will win. The others will delete their newly created object.
MyObj* g_singleton; // MyObj is some struct.
MyObj* GetMyObj()
{
MyObj* singleton;
if (g_singleton == NULL)
{
singleton = CreateNewObj();
// Only swap if the existing value is null. If not on Windows,
// use whatever compare and swap your platform provides.
if (InterlockCompareExchangePtr(&g_singleton, singleton, NULL) != NULL)
{
DeleteObj(singleton);
}
}
return g_singleton;
}
DoSomethingWithSingleton(GetMyObj());
Here's another perspective: every file in a C program is effectively a singleton class that is auto instantiated at runtime and cannot be subclassed.
Global static variables are your private class members.
Global non static are public (just declare them using extern in some header file).
Static functions are private methods
Non-static functions are the public ones.
Give everything a proper prefix and now you can use my_singleton_method() in lieu of my_singleton.method().
If your singleton is complex you can write a generate_singleton() method to initialize it before use, but then you need to make sure all the other public methods check if it was called and error out if not.
I think this solution might be the simplest and best for most use cases...
In this example, I am creating a single instance global dispatch queue, which you'd definitely do, say, if you were tracking dispatch source events from multiple objects; in that case, every object listening to the queue for events could be notified when a new task is added to the queue. Once the global queue is set (via queue_ref()), it can be referenced with the queue variable in any file in which the header file is included (examples are provided below).
In one of my implementations, I called queue_ref() in AppDelegate.m (main.c would work, too). That way, queue will be initialized before any other calling object attempts to access it. In the remaining objects, I simply called queue. Returning a value from a variable is much faster than calling a function, and then checking the value of the variable before returning it.
In GlobalQueue.h:
#ifndef GlobalQueue_h
#define GlobalQueue_h
#include <stdio.h>
#include <dispatch/dispatch.h>
extern dispatch_queue_t queue;
extern dispatch_queue_t queue_ref(void);
#endif /* GlobalQueue_h */
In GlobalQueue.c:
#include "GlobalQueue.h"
dispatch_queue_t queue;
dispatch_queue_t queue_ref(void) {
if (!queue) {
queue = dispatch_queue_create_with_target("GlobalDispatchQueue", DISPATCH_QUEUE_SERIAL, dispatch_get_main_queue());
}
return queue;
}
To use:
#include "GlobalQueue.h" in any Objective-C or C implementation source file.
Call queue_ref() to use the dispatch queue. Once queue_ref() has been called, the queue can be used via the queue variable in all source files
Examples:
Calling queue_ref():
dispatch_queue_t serial_queue_with_queue_target = dispatch_queue_create_with_target("serial_queue_with_queue_target", DISPATCH_QUEUE_SERIAL, **queue_ref()**);
Calling queue:
dispatch_queue_t serial_queue_with_queue_target = dispatch_queue_create_with_target("serial_queue_with_queue_target", DISPATCH_QUEUE_SERIAL, **queue**));]
Just do
void * getSingleTon() {
static Class object = (Class *)malloc( sizeof( Class ) );
return &object;
}
which works in a concurrent environment too.