Environment: NT Server 4.0 SP5, IIS with PHP4 ISAPI, php4isapi.dll, compiled in release_TS or debug_TS.

When I access a php page without extension module, every thing is fine.

When I access a php page singly with or without extension module, every thing is fine, too.

But if I access a php page parallelly with extension module, Access violation always occured. When I debug the php4isapi.dll in debug version, I found that when 2 connection access the php page, they runs in 2 threads. It seems that when thread 1 finish, it release memory thread 2 needed. And when thread 2 access those memory, access violation exception is occured.

The most often that access violation occured is in zend_opcode.c. happened at:

	if (opline->op1.op_type==IS_CONST) {

some memory address of op_array seems has been released,
and opline = op_array->opcodes is not a valid pointer anymore, that's why exception occured.

Below are the 2 call stacks of some situation:

1.
HttpExtensionProc
php_request_shutdown
zend_deactivate
shutdown_compiler
zend_hash_apply
zend_hash_apply_deleter
destroy_zend_function
destroy_op_array

2.
HttpExtensionProc
php_execute_script
execute
compile_filename
compile_files
v_compile_files
zendparse
do_begin_function_declaration
zend_hash_add_or_update
destroy_zend_function
destroy_op_array

They all happened after thread 1 is terminated.
If I modify some code:
in compiler_globals_ctor in zend.c
modify
    zend_hash_copy(compiler_globals->function_table, global_function_table, NULL, &tmp_func, sizeof(zend_function));
to
    zend_hash_copy(compiler_globals->function_table, global_function_table, (copy_ctor_func_t) function_add_ref, &tmp_func, sizeof(zend_function));

and 

in php_request_shutdown in main.c:

// shutdown_memory_manager(CG(unclean_shutdown), 0);

no access violation exception happened anymore.
I think it's too difficult to trace all code to find out why, and I don't think the modification is correct, because it may cause may memory allocated not be freed.