log.go

// +build android
package main

/*
#cgo LDFLAGS: -landroid
#include <jni.h>
#include <stdlib.h>

JavaVM* current_vm;
jobject current_ctx;

// 参考：https://github.com/golang/mobile/blob/master/internal/mobileinit/ctx_android.go
char* _lockJNI(uintptr_t* envp, int* attachedp) {
	JNIEnv* env;
	if (current_vm == NULL) {
		return "no current JVM";
	}
	*attachedp = 0;
	switch ((*current_vm)->GetEnv(current_vm, (void**)&env, JNI_VERSION_1_6)) {
	case JNI_OK:
		break;
	case JNI_EDETACHED:
		if ((*current_vm)->AttachCurrentThread(current_vm, &env, 0) != 0) {
			return "cannot attach to JVM";
		}
		*attachedp = 1;
		break;
	case JNI_EVERSION:
		return "bad JNI version";
	default:
		return "unknown JNI error from GetEnv";
	}
	*envp = (uintptr_t)env;
	return NULL;
}

char* _checkException(uintptr_t jnienv) {
	jthrowable exc;
	JNIEnv* env = (JNIEnv*)jnienv;
	if (!(*env)->ExceptionCheck(env)) {
		return NULL;
	}
	exc = (*env)->ExceptionOccurred(env);
	(*env)->ExceptionClear(env);
	jclass clazz = (*env)->FindClass(env, "java/lang/Throwable");
	jmethodID toString = (*env)->GetMethodID(env, clazz, "toString", "()Ljava/lang/String;");
	jobject msgStr = (*env)->CallObjectMethod(env, exc, toString);
	return (char*)(*env)->GetStringUTFChars(env, msgStr, 0);
}

void _unlockJNI() {
	(*current_vm)->DetachCurrentThread(current_vm);
}

void logd(JNIEnv* env, char *s) {
	jclass clsLog = (*env)->FindClass(env, "android/util/Log");
	jmethodID mthdD = (*env)->GetStaticMethodID(env, clsLog, "d", "(Ljava/lang/String;Ljava/lang/String;)I");
	jstring tag = (*env)->NewStringUTF(env, "MyLog");
	jstring message = (*env)->NewStringUTF(env, s);
	(*env)->CallStaticIntMethod(env, clsLog, mthdD, tag, message);
}
*/
import "C"

import (
	"errors"
	"runtime"
	"unsafe"
)

func runOnJVM(fn func(vm, env, ctx uintptr) error) error {
	errch := make(chan error)
	go func() {
		runtime.LockOSThread()
		defer runtime.UnlockOSThread()

		env := C.uintptr_t(0)
		attached := C.int(0)
		if errStr := C._lockJNI(&env, &attached); errStr != nil {
			errch <- errors.New(C.GoString(errStr))
			return
		}
		if attached != 0 {
			defer C._unlockJNI()
		}

		vm := uintptr(unsafe.Pointer(C.current_vm))
		if err := fn(vm, uintptr(env), uintptr(C.current_ctx)); err != nil {
			errch <- err
			return
		}

		if exc := C._checkException(env); exc != nil {
			errch <- errors.New(C.GoString(exc))
			C.free(unsafe.Pointer(exc))
			return
		}
		errch <- nil
	}()
	return <-errch
}

func logd(s string) {
	runOnJVM(func(vm, jniEnv, ctx uintptr) error {
		env := (*C.JNIEnv)(unsafe.Pointer(jniEnv))
		cs := C.CString(s)
		C.logd(env, cs)
		C.free(unsafe.Pointer(cs))
		return nil
	})
}