记录一次多线程同步导致的问题

出错日志：

01-08 15:32:44.677 10317 10317 F DEBUG   : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
01-08 15:32:44.677 10317 10317 F DEBUG   : Build fingerprint: 'PAX/unknown/unknown:10/QP1A.191105.004/eng.linmj.20210105.152410:userdebug/release-keys'
01-08 15:32:44.677 10317 10317 F DEBUG   : Revision: '0'
01-08 15:32:44.677 10317 10317 F DEBUG   : ABI: 'arm'
01-08 15:32:44.679 10317 10317 F DEBUG   : Timestamp: 2021-01-08 15:32:44+0800
01-08 15:32:44.679 10317 10317 F DEBUG   : pid: 3373, tid: 10308, name: Thread-111  >>> com.paxsz.irface.raysees <<<
01-08 15:32:44.679 10317 10317 F DEBUG   : uid: 1000
01-08 15:32:44.679 10317 10317 F DEBUG   : signal 6 (SIGABRT), code -1 (SI_QUEUE), fault addr --------
01-08 15:32:44.679 10317 10317 F DEBUG   : Abort message: 'JNI DETECTED ERROR IN APPLICATION: obj == null
01-08 15:32:44.679 10317 10317 F DEBUG   :     in call to CallVoidMethodV'
01-08 15:32:44.679 10317 10317 F DEBUG   :     r0  00000000  r1  00002844  r2  00000006  r3  b916ef50
01-08 15:32:44.680 10317 10317 F DEBUG   :     r4  b916ef64  r5  b916ef48  r6  00000d2d  r7  0000016b
01-08 15:32:44.680 10317 10317 F DEBUG   :     r8  b916ef60  r9  b916ef50  r10 b916ef80  r11 b916ef70
01-08 15:32:44.680 10317 10317 F DEBUG   :     ip  00002844  sp  b916ef20  lr  eddbdcb7  pc  eddbdcca
01-08 15:32:44.688 10317 10317 F DEBUG   :
01-08 15:32:44.688 10317 10317 F DEBUG   : backtrace:
01-08 15:32:44.688 10317 10317 F DEBUG   :       #00 pc 0005ecca  /apex/com.android.runtime/lib/bionic/libc.so (abort+166) (BuildId: 382e04da0c4d6d7d06edbd53601a5dd4)
01-08 15:32:44.689 10317 10317 F DEBUG   :       #01 pc 00382d71  /apex/com.android.runtime/lib/libart.so (art::Runtime::Abort(char const*)+1600) (BuildId: e321af3eb104ac43f13e5744596284b2)
01-08 15:32:44.692 10317 10317 F DEBUG   :       #02 pc 0000857d  /system/lib/libbase.so (android::base::LogMessage::~LogMessage()+412) (BuildId: 7a6528cfcb4efe233fdbfb73b5095897)
01-08 15:32:44.692 10317 10317 F DEBUG   :       #03 pc 0028e2d9  /apex/com.android.runtime/lib/libart.so (art::JavaVMExt::JniAbort(char const*, char const*)+1228) (BuildId: e321af3eb104ac43f13e5744596284b2)
01-08 15:32:44.692 10317 10317 F DEBUG   :       #04 pc 00011498  /data/app/com.paxsz.irface.raysees-vS3h2wW51ABPBuA9QmcUjQ==/lib/arm/libUVCCamera.so (_JNIEnv::CallVoidMethod(_jobject*, _jmethodID*, ...)+52) (BuildId: 8592169407668b052fad9bf72e38d511e33494c4)
01-08 15:32:44.692 10317 10317 F DEBUG   :       #05 pc 000113b4  /data/app/com.paxsz.irface.raysees-vS3h2wW51ABPBuA9QmcUjQ==/lib/arm/libUVCCamera.so (UVCPreview::do_capture_callback(_JNIEnv*, uvc_frame*)+244) (BuildId: 8592169407668b052fad9bf72e38d511e33494c4)
01-08 15:32:44.693 10317 10317 F DEBUG   :       #06 pc 00011064  /data/app/com.paxsz.irface.raysees-vS3h2wW51ABPBuA9QmcUjQ==/lib/arm/libUVCCamera.so (UVCPreview::do_capture(_JNIEnv*)+144) (BuildId: 8592169407668b052fad9bf72e38d511e33494c4)
01-08 15:32:44.693 10317 10317 F DEBUG   :       #07 pc 00010aac  /data/app/com.paxsz.irface.raysees-vS3h2wW51ABPBuA9QmcUjQ==/lib/arm/libUVCCamera.so (UVCPreview::capture_thread_func(void*)+64) (BuildId: 8592169407668b052fad9bf72e38d511e33494c4)
01-08 15:32:44.693 10317 10317 F DEBUG   :       #08 pc 000a6177  /apex/com.android.runtime/lib/bionic/libc.so (__pthread_start(void*)+20) (BuildId: 382e04da0c4d6d7d06edbd53601a5dd4)
01-08 15:32:44.693 10317 10317 F DEBUG   :       #09 pc 000601b1  /apex/com.android.runtime/lib/bionic/libc.so (__start_thread+30) (BuildId: 382e04da0c4d6d7d06edbd53601a5dd4)
01-08 15:32:44.768  1867  4667 I chatty  : uid=1041(audioserver) writer identical 7 lines
01-08 15:32:44.788  1867  4667 V audio_platform: mode(0),devices(0x2):platform device:OUT_DULSPK(0x4)
01-08 15:32:44.800  3373  4830 D DepthCalc: GetDepthByteData time: 426 [  784.827042] selinux: avc:  denied  { set } for property=persist.system.usbperm.disable pid=2237 uid=1000 gid=1000 scontext=u:r:system_server:s0 tcontext=u:object_r:default_prop:s0 tclass=property_service permissive=0
[  784.827042]

结合代码：

void UVCPreview::do_capture_callback(JNIEnv *env, uvc_frame_t *frame) {
    ENTER();

    if (LIKELY(frame)) {
        uvc_frame_t *callback_frame = frame;
        if (mFrameCallbackObj) {
            if (mFrameCallbackFunc) {
                callback_frame = get_frame(callbackPixelBytes);
                if (LIKELY(callback_frame)) {
                    int b = mFrameCallbackFunc(frame, callback_frame);
                    recycle_frame(frame);
                    if (UNLIKELY(b)) {
                        LOGW("failed to convert for callback frame");
                        goto SKIP;
                    }
                } else {
                    LOGW("failed to allocate for callback frame");
                    callback_frame = frame;
                    goto SKIP;
                }
            }
            jobject buf = env->NewDirectByteBuffer(callback_frame->data, callbackPixelBytes);
           //if(mFrameCallbackObj){
                env->CallVoidMethod(mFrameCallbackObj, iframecallback_fields.onFrame, buf);
           //}
            env->ExceptionClear();
            env->DeleteLocalRef(buf);
        }
 SKIP:
        recycle_frame(callback_frame);
    }
    EXIT();
}



原因：
多线程的问题，在调用env->CallVoidMethod(mFrameCallbackObj, iframecallback_fields.onFrame, buf);
mFrameCallbackObj已经被销毁了。正确的是应该加同步锁。我这里没有加，而是再一次判断非空。测试基本上不会在报错了。严格意义上还是要加同步锁，理论上我这样修改还是会低概率导致null报错。