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我有這樣的代碼：爲什麼這個JNI程序不能複製float值回Java端？
#if defined(NOT_STANDALONE)
JNIEXPORT void JNICALL sumTraces
(JNIEnv* env, jclass caller, jobjectArray jprestackTraces, jint nTracesIn, jobjectArray jsampleShifts,
jobjectArray jstartIndices, jobjectArray jnSamples, jobjectArray jstackTracesOut,
jobjectArray jpowerTracesOut, jint nTracesOut, jint samplesPerTrace) {
jboolean isCopy;
float* prestackTraces1D = (float*)malloc(nTracesIn * samplesPerTrace * sizeof(float));
if (prestackTraces1D == NULL) Fatal("Could not malloc prestackTraces1D");
int* sampleShifts1D = (int*)malloc(nTracesIn * nTracesOut * sizeof(int));
if (sampleShifts1D == NULL) Fatal("Could not malloc sampleShifts1D");
int* startIndices1D = (int*)malloc(nTracesIn * nTracesOut * sizeof(int));
if (startIndices1D == NULL) Fatal("Could not malloc startIndices1D");
int* nSamples1D = (int*)malloc(nTracesIn * nTracesOut * sizeof(int));
if (nSamples1D == NULL) Fatal("Could not malloc nSamples1D");
for (int in = 0; in < nTracesIn; in++) {
jfloatArray j_prestack = (jfloatArray)env->GetObjectArrayElement(jprestackTraces, in);
float* prestackTracesJava = (float*)env->GetPrimitiveArrayCritical(j_prestack, &isCopy);
for (int s = 0; s < samplesPerTrace; s++) {
int readIndex = s + (in * samplesPerTrace);
prestackTraces1D[readIndex] = prestackTracesJava[s];
}
env->ReleasePrimitiveArrayCritical(j_prestack, prestackTracesJava, JNI_ABORT);
}
for (int out = 0; out < nTracesOut; out++) {
jintArray j_shift = (jintArray)env->GetObjectArrayElement(jsampleShifts, out);
int* sampleShiftsJava = (int*)env->GetPrimitiveArrayCritical(j_shift, &isCopy);
jintArray j_start = (jintArray)env->GetObjectArrayElement(jstartIndices, out);
int* startIndicesJava = (int*)env->GetPrimitiveArrayCritical(j_start, &isCopy);
jintArray j_nSamps = (jintArray)env->GetObjectArrayElement(jnSamples, out);
int* nSamplesJava = (int*)env->GetPrimitiveArrayCritical(j_nSamps, &isCopy);
for (int in = 0; in < nTracesIn; in++) {
int readIndex = in + (out * nTracesIn);
sampleShifts1D[readIndex] = sampleShiftsJava[in];
startIndices1D[readIndex] = startIndicesJava[in];
nSamples1D[readIndex] = nSamplesJava[in];
}
env->ReleasePrimitiveArrayCritical(j_nSamps, nSamplesJava, JNI_ABORT);
env->ReleasePrimitiveArrayCritical(j_start, startIndicesJava, JNI_ABORT);
env->ReleasePrimitiveArrayCritical(j_shift, sampleShiftsJava, JNI_ABORT);
}
float* stackTracesOut1D = (float*)malloc(nTracesOut * samplesPerTrace * sizeof(float));
if (stackTracesOut1D == NULL) Fatal("Could not malloc stackTracesOut1D");
float* powerTracesOut1D = (float*)malloc(nTracesOut * samplesPerTrace * sizeof(float));
if (powerTracesOut1D == NULL) Fatal("Could not malloc powerTracesOut1D");
// Run the OpenCL program
ComputeTraces(prestackTraces1D, stackTracesOut1D, powerTracesOut1D,
startIndices1D, nSamples1D, sampleShifts1D,
samplesPerTrace, nTracesIn, nTracesOut,
0, 0, 1000);
// Free the arrays that we can
free(nSamples1D);
free(startIndices1D);
free(sampleShifts1D);
free(prestackTraces1D);
// Copy back the output for Java
for (int out = 0; out < nTracesOut; out++) {
jfloatArray j_stackOut = (jfloatArray)env->GetObjectArrayElement(jstackTracesOut, out);
jfloatArray j_powerOut = (jfloatArray)env->GetObjectArrayElement(jpowerTracesOut, out);
float* stackOutCopyBack = (float*)malloc(samplesPerTrace * sizeof(float));
float* powerOutCopyBack = (float*)malloc(samplesPerTrace * sizeof(float));
for (int s = 0; s < samplesPerTrace; s++) {
int readIndex = s + (out * samplesPerTrace);
stackOutCopyBack[s] = stackTracesOut1D[readIndex];
powerOutCopyBack[s] = powerTracesOut1D[readIndex];
}
for (int s = 0; s < samplesPerTrace; s++) {
printf("%d %f/%f\n", s, stackOutCopyBack[s], powerOutCopyBack[s]);
}
env->ReleasePrimitiveArrayCritical(j_stackOut, stackOutCopyBack, 0);
env->ReleasePrimitiveArrayCritical(j_powerOut, powerOutCopyBack, 0);
free(stackOutCopyBack);
free(powerOutCopyBack);
}
// Free the output arrays
free(powerTracesOut1D);
free(stackTracesOut1D);
}
的ComputeTraces（...）方法填充stackTracesOut1D和powerTracesOut1D陣列與值。我知道這些值是正確的，因爲在接近尾聲的for循環中有printf語句，我將它與我想要的值和它們匹配的值進行比較。但是，當我檢查Java端時，所有的值都被清零。爲什麼這個JNI代碼不能複製數據？
請記住，正如您在代碼中所看到的那樣，我必須將通過參數給出的2D數組濃縮到一維數組中，才能傳入函數。因此，在複製數據之前，我將更大的1D數組的一部分複製到較小的數組中，這是ReleasePrimitiveArrayCritical中的參數之一，但是這些值不會被複制回來。
編輯：只是要說清楚，我正在談論從最後10行起的線; env->ReleasePrimitiveArrayCritical(j_stackOut, stackOutCopyBack, 0);其中我使用的是0.
我沒有看到你在哪裏複製stackTracesOut1D或powerTracesOut1D到一個Java對象。你認爲它應該在哪裏複製？ –
在最後一個嵌入for循環內部（除了print語句），我在其中複製了一部分數據的行'stackOutCopyBack [s] = stackTracesOut1D [readIndex];''和'powerOutCopyBack [s] = powerTracesOut1D [readIndex]將這些數組添加到新創建的更小的數組中，該數組僅用於複製。 – danglingPointer
但是stackOutCopyBack和powerTracesOut1D沒有通過GetPrimitiveArrayCritical獲得。當指針沒有被獲得時，JNI文檔不清楚這裏發生了什麼。事實上，mode = 0似乎是錯誤的，因爲ReleasePrimitiveArrayCritical可能釋放指針。有沒有理由不重寫它使用GetPrimitiveArrayCritical？ –