MATLAB appcrash when I use mxFree in S-Function
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hi, I'm studying a C mex s-function. I wrote following C++ code.
#define S_FUNCTION_NAME sfun_exam
#define S_FUNCTION_LEVEL 2
#include "simstruc.h"
#include "matrix.h" // for mxMalloc
#include <stdlib.h>
#define FALSE 0
#define TRUE 1
#define NUM_INPUTS 0
#define NUM_OUTPUTS 0
#define NUM_PARAMS 0
#define NUM_CONT_STATE 0
#define NUM_DISC_STATE 0
static void mdlInitializeSizes(SimStruct *S)
{
ssPrintf("mdlInitializeSizes entry\n");
ssSetNumSFcnParams(S, NUM_PARAMS);
//ssSetSFcnParamTunable(S, 0, 0);
ssSetNumContStates(S, NUM_CONT_STATE);
ssSetNumDiscStates(S, NUM_DISC_STATE);
if (!ssSetNumInputPorts(S, NUM_INPUTS)) return;
if (!ssSetNumOutputPorts(S, NUM_OUTPUTS)) return;
ssSetNumSampleTimes(S, 1);
ssSetNumRWork(S, 0);
ssSetNumIWork(S, 0);
ssSetNumPWork(S, 1);
ssSetNumModes(S, 0);
ssSetNumNonsampledZCs(S, 0);
ssSetSimStateCompliance(S, USE_DEFAULT_SIM_STATE);
ssSetOptions(S, 0);
ssPrintf("mdlInitializeSizes exit\n");
}
static void mdlInitializeSampleTimes(SimStruct *S)
{
ssPrintf("mdlInitializeSampleTimes entry\n");
ssPrintf("mdlInitializeSampleTimes exit\n");
}
#define MDL_START
static void mdlStart(SimStruct *S)
{
ssPrintf("mdlStart entry\n");
double *temp = (double *)mxMalloc(sizeof(double));
ssPrintf("assigned address = %d\n", temp);
ssGetPWork(S)[0] = (void *)temp;
ssPrintf("mdlStart exit\n");
}
static void mdlOutputs(SimStruct *S, int_T tid)
{
ssPrintf("mdlOutputs entry\n");
UNUSED_ARG(tid);
ssPrintf("mdlOutputs exit\n");
}
static void mdlTerminate(SimStruct *S)
{
ssPrintf("mdlTerminate entry\n");
void *temp;
temp = ssGetPWork(S)[0];
ssPrintf("assigned address = %d\n", temp);
mxFree(temp);
ssPrintf("mdlTerminate exit\n");
}
/*=============================*
* Required S-function trailer *
*=============================*/
#ifdef MATLAB_MEX_FILE /* Is this file being compiled as a MEX-file? */
#include "simulink.c" /* MEX-file interface mechanism */
#else
#include "cg_sfun.h" /* Code generation registration function */
#endif
It is built without error. but during simulation, MATLAB appcrash occured.
Problem signature
Problem Event Name: APPCRASH
Application Name: MATLAB.exe
Application Version: 7.13.0.0
Application Timestamp: 4e4754eb
Fault Module Name: StackHash_b9f6
Fault Module Version: 6.1.7601.17725
Fault Module Timestamp: 4ec49b60
Exception Code: c0000374
Exception Offset: 000c380b
OS Version: 6.1.7601.2.1.0.256.48
Locale ID: 1042
Additional Information 1: b9f6
Additional Information 2: b9f67d14f6a48d7204fa389a0a5bf0d1
Additional Information 3: c4cc
Additional Information 4: c4ccbe39e350b9853267802fd89da65d
When I used malloc and free Instead of mxMalloc and mxFree, this appcrash didn't occur.
what did I do wrong??
thanks for reading..
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추가 답변 (2개)
Kaustubha Govind
2012년 3월 2일
ssGetPWork(S) returns memory owned and managed by Simulink - you should not be freeing this memory in your own code. Is there a reason you want to do this? Also, I don't know why mxFree crashes, but free doesn't. My guess is that mxFree does some extra checking or book-keeping that detects the segmentation violation, whereas free is failing to detect it.
댓글 수: 5
Kaustubha Govind
2012년 3월 6일
Oops, sorry, just realized you are using PWorks, and not DWorks. You do need to allocate and free memory for PWorks yourself. I think Friedrich's answer is correct.
James Tursa
2012년 3월 2일
I know nothing about S-functions, but to hazard a guess maybe you need to NULL out the array value after you manually free the memory so that something in the background doesn't see this value and try to free it again even though the pointer is no longer valid. E.g., maybe add the last line shown:
temp = ssGetPWork(S)[0];
ssPrintf("assigned address = %d\n", temp);
mxFree(temp);
ssGetPWork(S)[0] = NULL; /* add this line */
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