Help: call_user_function() core dumps

I am new to PHP extension writing and embedding. Following the book from
Sara Goleman - Extending and Embedding PHP (Developer's Library)
I wrote the following program based on her example in Chap. 20

===================================================================
#include <stdio.h>
#include <stdlib.h>

#include <sapi/embed/php_embed.h>

int main(int argc, char** argv) {
PHP_EMBED_START_BLOCK(argc, argv);

zval* args[2];
zval funcname;
zval input_str;
zval count;
zval retval;
char* ans;
  ZVAL_STRING(&funcname, "str_repeat", 0);
args[0] = &input_str;
args[1] = &count;
ZVAL_STRINGL(args[0], "DHIRU ", 6, 0);
ZVAL_LONG(args[1], 5L);
  call_user_function(EG(function_table), NULL, &funcname, &retval, 2, args TSRMLS_CC);
  ans = Z_STRVAL(retval);
printf("%s\n", ans);
  PHP_EMBED_END_BLOCK();
  return 0;

}

========================================================================

When I run this program it core dumps with the following message:

/export/home/dhiru/work/php/php-5.2.5/Zend/zend_variables.h(35) : Block 0x08049188 status:
/export/home/dhiru/work/php/php-5.2.5/Zend/zend_variables.c(36) : Actual location (location was relayed)
Invalid pointer: ((thread_id=0x4C45535F) != (expected=0xB78D26B0))
Segmentation fault (core dumped)

When I step thru the debugger it appears that the function str_repeat call is successful
via zend_call_function(), but after the call to the str_repeat function it tries to execute
zend_ptr_stack_clear_multiple(TSRMLS_C), which in turn calls zend_mm_check_ptr() and something
seems to go wrong here :

#ifdef ZTS
if (ZEND_MM_BAD_THREAD_ID(p)) {
if (!silent) {
zend_debug_alloc_output("Invalid pointer: ((thread_id=0x%0.8X) != (expected=0x%0.8X))\n", (long)p->thread_id,
(long)tsrm_thread_id());
had_problems = 1;
} else {
return zend_mm_check_ptr(heap, ptr, 0 ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_ORIG_RELAY_CC);
}
}
#endif

Any help will be greatly appreciated

Thanks,
-Dhiru
P.S.: I am using Ubuntu and PHP 5.2.5