Question

I’ve got a problem of execution with a C++ program. First of all, I’m working on a MacBook Pro, using native g++ to compile.

My program builds an array of Record*. Each record has a multidimensional key. Then it iterates over each record to find its unidimensional float key.

In the end, given an interval of two multidimensional keys, it determines if a given float corresponds to a multidimensional key in this interval. The algorithm is taken from a research paper, and it is quite simple in implementation.

Until 100,000 values computed, no problem, the program does its job. But when I goes to 1,000,000 values, execution crashes.Here is the error given by g++ :

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x00007fff5f08dcd0
0x00000001000021ab in TestPyramid () at include/indextree_test.cc:444

Here is the full backtrace given by gdb :

(gdb) backtrace full
#0  0x00000001000021ab in TestPyramid () at include/indextree_test.cc:444
test_records = #1  0x00000001000027be in main (argc=<value temporarily unavailable, due to optimizations>, argv=0x7fff5fbff8f8) at include/indextree_test.cc:83
rc = <value temporarily unavailable, due to optimizations>
progName = 0x7fff5fbff9f8 "/Users/Max/Documents/indextree_test"
testNum = 4

Given lines are calls to the function.

Here is a sample of code :

Record* test_records[1000000];
float values[1000000];
int base = 0;

for (int i(0); i < 1000000; i++)
{
    test_records[i] = CreateRecordBasic(i%30+10,i+i%100,"ab","Generic Payload");
    if (i%30+10 > base)
        base = i%30+10;
    if (i+10*i > base)
        base = i+10*i;
    if (i > base)
        base = i;
}

for (int i(0); i < 1000000; i++)
    values[i] = floatValueFromKey(test_records[i]->key, base,num_char);

And in the end, I put the relevant float keys in a list.

Is the problem a limitation of my computer ? Did I allocate the memory in a bad manner ?

Thanks for your help,

Max.

Edit :

Here is the code of CreateRecordBasic :

Record *CreateRecordBasic(int32_t attribute_1, int64_t attribute_2, const char* attribute_3, const char* payload){
    Attribute** a = new Attribute*[3];

    a[0] = ShortAttribute(attribute_1);
    a[1] = IntAttribute(attribute_2);
    a[2] = VarcharAttribute(attribute_3);

    Record *record = new Record;
    record->key.value = a;
    record->key.attribute_count = 3;
    SetValue(record->payload,payload);

    return record;
}

Answer 1

Record* test_records[1000000];
float values[1000000];

IMHO, these variables are too big to be stored in the stack whose size is defined by your environment. values takes up 4 megabytes and test_records may take 4-8 megabytes, this is pretty big amount of stack-space. Compiler does not exactly know the size of the system-allocated stack (this may change from system to system) , so you get the error at run-time. Try to allocate them on the heap…