Why am I getting a memory access violation here?

This file is part of the GoAhead WebServer, that implements a very fast block allocation scheme.

At line 284 the web server process crashes, at random times.

 } else if ((bp = bQhead[q]) != NULL) {
/*
 *  Take first block off the relevant q if non-empty
 */
  bQhead[q] = bp->u.next; //MEMORY ACCESS VIOLATION HERE

What are the possible reasons for this?

EDIT

bp is a pointer to this structure and union in this header file

typedef struct {
    union {
        void    *next;    开发者_JS百科                      /* Pointer to next in q */
        int     size;                           /* Actual requested size */
    } u;
    int         flags;                          /* Per block allocation flags */
} bType;

Thanks.

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Here's the possible reasons.

• You've screwd something up and corrupted some of your data structures or your stack.

• bQhead is a NULL or invalid pointer

• q is outside the bounds of bQhead

• bp is a NULL or invalid pointer

Step through the code with a debugger, or use printf debugging, and see if the values if bQhead,q,bp are what they should be.

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Give us more hints ...

Probably memory corruption by another thread, if it is random ...

my2c

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Without running under a debugger, I would guess that q is out of range of 0 to B_MAXCLASS-1. The function that sets q, ballocGetSize() does not do any bounds checking to make sure the block class stays within bounds.

A simple assertion to check that q is within bounds before deferencing would rule that possibilty out.