Zend Memory Manager
===================

General:
--------

The goal of the new memory manager (available since PHP 5.2) is to reduce memory
allocation overhead and speedup memory management.

The new manager's "configure" has no "--disable-zend-memory-manager" option,
but it has "--enable-malloc-mm" instead.  It is enabled by default in DEBUG
build and disabled by default in RELEASE build. When enabled it allows selecting
between malloc and emalloc at runtime so you can use internal and external memory
debuggers without recompilation.

Debugging:
----------

Normal:

    $ sapi/cli/php -r 'leak();'

Zend MM disabled:

    $ USE_ZEND_ALLOC=0 valgrind --leak-check=full sapi/cli/php -r 'leak();'

Shared extensions:
------------------

Since PHP 5.3.11 it is possible to prevent shared extensions from unloading so
that valgrind can correctly track the memory leaks in shared extensions. For
this there is the ZEND_DONT_UNLOAD_MODULES environment variable. If set, then
DL_UNLOAD() is skipped during the shutdown of shared extensions.


Tweaking:
---------

The Zend MM can be tweaked using ZEND_MM_MEM_TYPE and ZEND_MM_SEG_SIZE environment
variables.  Default values are "malloc" and "256K". Dependent on target system you
can also use "mmap_anon", "mmap_zero" and "win32" storage managers.

	$ ZEND_MM_MEM_TYPE=mmap_anon ZEND_MM_SEG_SIZE=1M sapi/cli/php ..etc.

ZEND_VM
=======

ZEND_VM architecture allows specializing opcode handlers according to op_type
fields and using different execution methods (call threading, switch threading
and direct threading). As a result ZE2 got more than 20% speedup on raw PHP
code execution (with specialized executor and direct threading execution
method). As in most PHP applications raw execution speed isn't the limiting
factor but system calls and database calls are, your mileage with this patch
will vary.

Most parts of the old zend_execute.c go into zend_vm_def.h. Here you can
find opcode handlers and helpers. The typical opcode handler template looks
like this:

ZEND_VM_HANDLER(<OPCODE-NUMBER>, <OPCODE>, <OP1_TYPES>, <OP2_TYPES>)
{
	<HANDLER'S CODE>
}

<OPCODE-NUMBER> is a opcode number (0, 1, ...)
<OPCODE> is an opcode name (ZEN_NOP, ZEND_ADD, :)
<OP1_TYPES> & <OP2_TYPES> are masks for allowed operand op_types. Specializer
will generate code only for defined combination of types. You can use any
combination of the following op_types UNUSED, CONST, VAR, TMP and  CV also
you can use ANY mask to disable specialization according operand's op_type.
<HANDLER'S CODE> is a handler's code itself. For most handlers it stills the
same as in old zend_execute.c, but now it uses macros to access opcode operands
and some internal executor data.

You can see the conformity of new macros to old code in the following list:

EXECUTE_DATA
	execute_data
ZEND_VM_DISPATCH_TO_HANDLER(<OP>)
	return <OP>_helper(ZEND_OPCODE_HANDLER_ARGS_PASSTHRU)
ZEND_VM_DISPATCH_TO_HELPER(<NAME>)
	return <NAME>(ZEND_OPCODE_HANDLER_ARGS_PASSTHRU)
ZEND_VM_DISPATCH_TO_HELPER_EX(<NAME>,<PARAM>,<VAL>)
	return <NAME>(<VAL>, ZEND_OPCODE_HANDLER_ARGS_PASSTHRU)
ZEND_VM_CONTINUE()
	return 0
ZEND_VM_NEXT_OPCODE()
	NEXT_OPCODE()
ZEND_VM_SET_OPCODE(<TARGET>
	SET_OPCODE(<TARGET>
ZEND_VM_INC_OPCODE()
	INC_OPCOD()
ZEND_VM_RETURN_FROM_EXECUTE_LOOP()
	RETURN_FROM_EXECUTE_LOOP()
ZEND_VM_C_LABEL(<LABEL>):
	<LABEL>:
ZEND_VM_C_GOTO(<LABEL>)
	goto <LABEL>
OP<X>_TYPE
	opline->op<X>.op_type
GET_OP<X>_ZVAL_PTR(<TYPE>)
	get_zval_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
GET_OP<X>_ZVAL_PTR_PTR(<TYPE>)
	get_zval_ptr_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
GET_OP<X>_OBJ_ZVAL_PTR(<TYPE>)
	get_obj_zval_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
GET_OP<X>_OBJ_ZVAL_PTR_PTR(<TYPE>)
	get_obj_zval_ptr_ptr(&opline->op<X>, EX(Ts), &free_op<X>, <TYPE>)
IS_OP<X>_TMP_FREE()
	IS_TMP_FREE(free_op<X>)
FREE_OP<X>()
	FREE_OP(free_op<X>)
FREE_OP<X>_IF_VAR()
	FREE_VAR(free_op<X>)
FREE_OP<X>_VAR_PTR()
	FREE_VAR_PTR(free_op<X>)


Executor's helpers can be defined without parameters or with one parameter.
This is done with the following constructs:

ZEND_VM_HELPER(<HELPER-NAME>, <OP1_TYPES>, <OP2_TYPES>)
{
	<HELPER'S CODE>
}

ZEND_VM_HELPER_EX(<HELPER-NAME>, <OP1_TYPES>, <OP2_TYPES>, <PARAM_SPEC>)
{
	<HELPER'S CODE>
}

Executor's code is generated by PHP script zend_vm_gen.php it uses zend_vm_def.h
and zend_vm_execute.skl as input and produces zend_vm_opcodes.h and
zend_vm_execute.h. The first file is a list of opcode definitions. It is
included from zend_compile.h. The second one is an executor code itself. It is
included from zend_execute.c.

zend_vm_gen.php can produce different kind of executors. You can select
different opcode threading model using --with-vm-kind=CALL|SWITCH|GOTO. You can
disable opcode specialization using --without-specializer. You can include or
exclude old executor together with specialized one using --without-old-executor.
At last you can debug executor using original zend_vm_def.h or generated file
zend_vm_execute.h. Debugging with original file requires --with-lines
option. By default ZE2 uses the following command to generate executor:

$ php zend_vm_gen.php --with-vm-kind=CALL

Zend Engine II currently includes two executors during the build process, one
is the specialized version and the other is the old one non-specialized with
function handlers. By default Zend Engine II uses the specialized one but you
can switch to the old executor at runtime by calling zend_vm_use_old_executor().

Last Index update Tue Apr 23 16:02:41 UTC 2024

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