Android NDK jshortArray 没有宣传的那么长

Question

我遇到以下代码的段错误:

#include <stddef.h>
#include <android/log.h>
#include "com_backyardbrains_drawing_BybGLDrawable.h"

#define ALOG(msg) __android_log_print(ANDROID_LOG_DEBUG, "NDK:BYB", msg)
#define AERR(msg) __android_log_print(ANDROID_LOG_ERROR, "NDK:BYB", msg)

JNIEXPORT jfloatArray JNICALL
Java_com_backyardbrains_drawing_BybGLDrawable_interleaveXvalues
(JNIEnv *env, jclass clazz, jshortArray shortArrayToDraw) {
ALOG("called interleave");

    jfloatArray result;
    jsize len = (*env)->GetArrayLength(env, shortArrayToDraw);
    __android_log_print(ANDROID_LOG_DEBUG, "NDK:BYB",
                       "Got input length of %d", len);
    jshort *valuesjs = (*env)->GetShortArrayElements(env, shortArrayToDraw, NULL);
    if (valuesjs == NULL || !(len > 0)) {
        return NULL;
    }
    jfloat tmp[len*2];
    __android_log_print(ANDROID_LOG_DEBUG, "NDK:BYB",
                  "made a new tmp array of size %d",
                  sizeof(tmp)/sizeof(jfloat));
    // Create the returnable 2D array
    result = (*env)->NewFloatArray(env, len*2);
    if (result == NULL) {
        AERR("could not allocate result");
        return NULL;
    }

    int i;
    for (i = 0; i < len; i++) {
        tmp[i*2] = i;
        tmp[i*2+1] = valuesjs[i];
        __android_log_print(ANDROID_LOG_DEBUG, "NDK:BYB", "Set element %d", i);
    }
    ALOG("Finished building new array");

    (*env)->ReleaseShortArrayElements(env, shortArrayToDraw, valuesjs, 0);
    ALOG("released old short array");

    (*env)->SetFloatArrayRegion(env, result, 0, len*2, tmp);
    ALOG("set new float array");
    return result;

}

日志输出是这样的:

06-19 21:34:24.829 29156 29172 D NDK:BYB : called interleave
06-19 21:34:24.829 29156 29172 D NDK:BYB : Got input length of 131072
06-19 21:34:24.829 29156 29172 D NDK:BYB : made a new tmp array of size 262144            
06-19 21:34:25.157 29156 29172 D NDK:BYB : Set element 0
... 
06-19 21:34:25.157 29156 29172 D NDK:BYB : Set element 158
06-19 21:34:25.367 29204 29204 I DEBUG   : pid: 29156, tid: 29172  >>> com.backyardbrains <<<
06-19 21:34:25.367 29204 29204 I DEBUG   : signal 11 (SIGSEGV), code 2 (SEGV_ACCERR), fault addr 450ac000

对于 for 循环，问题始终出现在 159 for i 处。但是，传入此函数的数组的预期长度是固定的 131072 个元素(如日志中所示)。为什么数组下方的值无法访问？

Answer 1

也许您的环境无法很好地处理在堆栈上分配的如此多的内存。因为 sizeof(tmp) == 1 MB。尝试在堆上分配 tmp。