As a result of an engine rewrite with focus on more efficient data structures, PHP 7 offers much improved performance and memory usage. This session describes important aspects of the new implementation and how it compares to PHP 5. A particular focus will be on the representation of values, arrays and objects.

1. PHP 7
What changed internally?
Nikita Popov

2. •Return type declarations
•Scalar type declarations
function startsWith(string $s1, string $s2) : bool {…}

3. 211
254 256 273
627
666
0
100
200
300
400
500
600
700
PHP 5.3 PHP 5.4 PHP 5.5 PHP 5.6 PHP 7 HHVM 3.7
Req/Sec
Wordpress 4.1.1 (home, 20 c)
Stolen from Rasmus

4. •Smaller data structures
•Fewer allocations
•Less indirection

5. zval

6. zval
5

7. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
5

8. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
lval (long)
dval (double)
5

9. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
lval (long)
dval (double)
5
64 bits / 8 bytes

10. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
lval (long)
dval (double)
lval (long)
1 bit
5

11. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
val (char *)
len (int)
A B C 0
5

12. value
ty
5

13. value
refcount ty
5

14. value = LONG(42)
refcount = 1$i
$i = 42;
5

15. value = LONG(42)
refcount = 2$i
$j
$i = 42;
$j = $i;
5

16. value = LONG(42)
refcount = 3$i
$j
$k
$i = 42;
$j = $i;
$k = $i;
5

17. value = LONG(42)
refcount = 1
$i = 42;
$j = $i;
$k = $i;
unset($i, $k);
5
$j

18. value = LONG(42)
refcount = 0
$i = 42;
$j = $i;
$k = $i;
unset($i, $k);
unset($j);
5

19. value = LONG(42)
refcount = 0
$i = 42;
$j = $i;
$k = $i;
unset($i, $k);
unset($j);
free( )
5

20. value = ARRAY
refcount = 1$a
$a = [];
5
[0]: (empty)
[1]: (empty)
[2]: (empty)
…

21. value = ARRAY
refcount = 2$a
$a = [];
$a[0] = $a;
5
[0]:
[1]: (empty)
[2]: (empty)
…

22. value = ARRAY
refcount = 1
$a = [];
$a[0] = $a;
unset($a);
5
[0]:
[1]: (empty)
[2]: (empty)
…

23. value = ARRAY
refcount = 1
$a = [];
$a[0] = $a;
unset($a);
5
[0]:
[1]: (empty)
[2]: (empty)
…
[0]: (empty)
[1]: (empty)
[2]: (empty)
…
GC root buffer

24. value = ARRAY
refcount = 1
$a = [];
$a[0] = $a;
unset($a);
5
[0]:
[1]: (empty)
[2]: (empty)
…
[0]:
[1]: (empty)
[2]: (empty)
…
GC root buffer

25. value = ARRAY
refcount = 1
gc_root
$a = [];
$a[0] = $a;
unset($a);
5
[0]:
[1]: (empty)
[2]: (empty)
…
[0]:
[1]: (empty)
[2]: (empty)
…
GC root buffer

26. value
refcount ty
gc_root
5

27. size
prev_size
value
refcount ty
gc_root
5

28. size
prev_size
value
refcount ty
gc_root
5
32 bytes
16 bytes

29. value
type_info (u2)
7

30. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
5

31. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
7
FALSE
TRUE

32. NULL
BOOL
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
REFERENCE 7
FALSE
TRUE

33. NULL
FALSE
TRUE
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
REFERENCE
val (char *)
len (int)
A B C 0
5

34. NULL
FALSE
TRUE
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
REFERENCE 7
zend_string *
refcount type_info
hash
len (size_t)
A B C 0

35. NULL
FALSE
TRUE
LONG
DOUBLE
STRING
ARRAY
OBJECT
RESOURCE
REFERENCE 7
zend_string *
refcount type_info
hash
len (size_t)
A B C 0
refcounted header

36. $i = 42;
7
$i value = 42
LONG

37. $i = 42;
$j = $i;
7
$i value = 42
LONG
$j value = 42
LONG

38. $i = 42;
$j = $i;
$k = $i;
7
$i value = 42
LONG
$j value = 42
LONG
$k value = 42
LONG

39. $s = “foobar”;
7
$s value
STRING
refcount = 1 type_info
hash = 0x80000652FDE460BE
len = 6
f o o b a r 0

40. $s = “foobar”;
$t = $s;
7
$s value
STRING
$t value
STRING refcount = 2 type_info
hash = 0x80000652FDE460BE
len = 6
f o o b a r 0

41. $s = “foobar”;
$t = $s;
$u = $s;
7
$s value
STRING
$t value
STRING
$u value
STRING
refcount = 3 type_info
hash = 0x80000652FDE460BE
len = 6
f o o b a r 0

42. 7
refcount type_info
hash
len (size_t)
A B C 0
refcounted header

43. 7
refcount type_info
hash
len (size_t)
A B C 0
refcounted header
type flags gc_info

44. 7
refcount type_info
hash
len (size_t)
A B C 0
refcounted header
type flags gc_info
INTERNED
etc.

45. value
type_info (u2)
7

46. value
type_info (u2)
7
type type_flags const_flags

47. 7
type type_flags const_flags
refcounted collectable copyable
simple types
string
interned string
array
object
resource
reference

48. 7
type type_flags const_flags
refcounted collectable copyable
simple types
string 
interned string
array 
object 
resource 
reference 

49. 7
type type_flags const_flags
refcounted collectable copyable
simple types
string 
interned string
array  
object  
resource 
reference 

50. 7
type type_flags const_flags
refcounted collectable copyable
simple types
string  
interned string
array   
object  
resource 
reference 

51. 5
array == HashTable

52. 5
key = “foo”
idx = hash(“foo”)

53. 5
key = “foo”
idx = hash(“foo”) % tableSize

54. 5
[0]: (empty)
[1]: (empty)
[2]: (empty)
[3]: (empty)
“foo”

55. 5
[0]: (empty)
[1]:
[2]: (empty)
[3]: (empty)
“foo”
data
key “foo”
zval

56. 5
[0]: (empty)
[1]:
[2]: (empty)
[3]: (empty)
“foo”
data
key “foo”
“bar”

57. 5
[0]: (empty)
[1]:
[2]: (empty)
[3]: (empty)
“foo”
data
key “foo”
next
“bar”
data
key “bar”
next = NULL

58. 5
[0]: (empty)
[1]:
[2]: (empty)
[3]: (empty)
“foo”
data
key “foo”
next
prev = NULL
“bar”
data
key “bar”
next = NULL
prev

59. 5
data
prev
next
key “foo”
zval

60. 5
data
listNext
listPrev
prev
next
key “foo”
zval
$a1 = [“foo” => 1,
“bar” => 2];
$a2 = [“bar” => 2,
“foo” => 1];

61. 5
dataPtr
data
listNext
listPrev
prev
next
key “foo”
zval

62. 5
hash
keyLen
dataPtr
data
listNext
listPrev
prev
next
key “foo”
zval

63. 7
hash
key
value
type_info next
zval

64. 7
hash
key
value
type_info next
refcount type_info
hash
len
f o o 0
zend_string

65. 7
hash
key
value
type_info next
hash
key
value
type_info next
hash
key
value
type_info next

66. 7
hash
key
value
type_info next
hash
key
value
type_info next
hash
key
value
type_info next
[0]
[1]
[2]
[3]

67. 7
hash
key
value
type_info next
hash
key
value
type_info next
hash
key
value
type_info next
[0] = -1
[1] = -1
[2] = -1
[3] = -1
$a = [];
numUsed = 0

68. 7
hash
key
value = 42
LONG next = -1
hash
key
value
type_info next
hash
key
value
type_info next
[0] = -1
[1] = 0
[2] = -1
[3] = -1
“foo”
$a = [];
$a[“foo”] = 42;
“foo”
numUsed = 1

69. 7
hash
key
value = 42
LONG next = -1
hash
key
value = 24
LONG next = -1
hash
key
value
type_info next
[0] = -1
[1] = 0
[2] = -1
[3] = 1
“foo”
$a = [];
$a[“foo”] = 42;
$a[“bar”] = 24; “foo”
“bar”
“bar”
numUsed = 2

70. 7
hash
key
value = 42
LONG next = 2
hash
key
value = 24
LONG next = -1
hash
key
value = 3.141
DOUBLE next = -1
[0] = -1
[1] = 0
[2] = -1
[3] = 1
“foo”
$a = [];
$a[“foo”] = 42;
$a[“bar”] = 24;
$a[“xyz”] = 3.141;
“foo”
“bar”
“bar”
“xyz”
“xyz”

71. 7
hash
key
value
UNDEF next = -1
hash
key
value = 24
LONG next = -1
hash
key
value = 3.141
DOUBLE next = -1
[0] = -1
[1] = 2
[2] = -1
[3] = 1
$a = [];
$a[“foo”] = 42;
$a[“bar”] = 24;
$a[“xyz”] = 3.141;
unset($a[“foo”]);
“bar”
“bar”
“xyz”
“xyz”

72. 7
hash
key
value
type_info next
hash
key
value
type_info next
[0]
[1]
[2]
[3]
[4]
[5]
[6]
[7]

73. 7
hash
key
value
type_info next
hash
key
value
type_info next
[0] [1]
[2] [3]
[4] [5]
[6] [7]

74. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]

75. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data

76. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
data / hash pointer
numUsed

77. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
tableMask
data / hash pointer
numUsed
tableSize
tableMask = -tableSize

78. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
tableMask
data / hash pointer
numUsed
tableSize
1010111010110110
tableMask = -tableSize

79. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
tableMask
data / hash pointer
numUsed
tableSize
1010111010110110
| 1111111111100000
tableMask = -tableSize

80. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
tableMask
data / hash pointer
numUsed
tableSize
1010111010110110
| 1111111111100000
= 1111111111110110 = -10
tableMask = -tableSize

81. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
tableMask
data / hash pointer
numUsed numElems
tableSize
nextFreeElement

82. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
tableMask
data / hash pointer
numUsed numElems
tableSize internalPtr
nextFreeElement
destructor

83. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
flags tableMask
data / hash pointer
numUsed numElems
tableSize internalPtr
nextFreeElement
destructor
flags applyCnt iterCnt

84. 7
hash
key
value
type_info next
hash
key
value
type_info next
[-8] [-7]
[-6] [-5]
[-4] [-3]
[-2] [-1]
hash
data
refcount type_info
flags tableMask
data / hash pointer
numUsed numElems
tableSize internalPtr
nextFreeElement
destructor
flags applyCnt iterCnt
PACKED
etc.

85. 7
hash
key
value
type_info next
hash
key
value
type_info next
data
refcount type_info
flags tableMask
data pointer
numUsed numElems
tableSize internalPtr
nextFreeElement
destructor
flags applyCnt iterCnt
PACKED
etc.

86. 5
objects

87. 5
handle (ID)
handlers
zval value

88. 5
handle (ID)
handlers
zval value
handler table
object store bucket

89. 5
handle (ID)
handlers
zval value
…
read_prop()
write_prop()
…
object store bucket

90. 5
handle (ID)
handlers
zval value
…
read_prop()
write_prop()
…
object
object store bucket
actual object

91. 5
handle (ID)
handlers
zval value
…
read_prop()
write_prop()
…
object
refcount
object store bucket
actual object

92. 5
handle (ID)
handlers
zval value
…
read_prop()
write_prop()
…
object
dtor()
free_storage()
clone()
refcount
object store bucket
actual object

93. 5
handle (ID)
handlers
zval value
…
read_prop()
write_prop()
…
object
dtor()
free_storage()
clone()
handlers
refcount
gc_root
object store bucket
actual object

94. 5
handle (ID)
handlers
zval value
…
read_prop()
write_prop()
…
D V ac
object
dtor()
free_storage()
clone()
handlers
refcount
gc_root
object store bucket
actual object

95. 5
object store bucket
standard object

96. 5
object store bucket
ce
standard object
zend_class_entry

97. 5
object store bucket
ce
properties
standard object
zend_class_entry
HashTable for
dynamic properties

98. 5
object store bucket
ce
properties
properties_table
standard object
zend_class_entry
HashTable for
dynamic properties
[0] (stores $prop1)
[1] (stores $prop2)
[2] (stores $prop3)
zval
zval
zval

99. 5
object store bucket
ce
properties
properties_table
guards
standard object
zend_class_entry
HashTable for
dynamic properties
[0] (stores $prop1)
[1] (stores $prop2)
[2] (stores $prop3)
zval
zval
zval
HashTable for
__get etc. guards

100. 5
object store bucket
ce
properties
properties_table
guards
custom extension
for internal object
standard object
zend_class_entry
HashTable for
dynamic properties
[0] (stores $prop1)
[1] (stores $prop2)
[2] (stores $prop3)
zval
zval
zval
HashTable for
__get etc. guards

101. 7
zend_object *
refcount type_info
ce
properties
zend_class_entry
HashTable for
dynamic properties

102. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
zend_class_entry
HashTable for
dynamic properties
handler table

103. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
zend_class_entry
HashTable for
dynamic properties
handler table
object store

104. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
value
type_info
value
type_info
value
type_info
zend_class_entry
HashTable for
dynamic properties$prop1 zval
$prop2 zval
$prop3 zval
handler table
object store

105. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
value
type_info
value
type_info
value
type_info
zend_class_entry
HashTable for
dynamic properties
HashTable for
__get etc. guards
guards zval
$prop1 zval
$prop2 zval
handler table
object store

106. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
value
type_info
value
type_info
value
type_info
zend_class_entry
HashTable for
dynamic properties
HashTable for
__get etc. guards
guards zval
$prop1 zval
$prop2 zval
handler table
object store
ext. for internal objects

107. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
value
type_info
value
type_info
value
type_info
zend_class_entry
HashTable for
dynamic properties
HashTable for
__get etc. guards
guards zval
$prop1 zval
$prop2 zval
handler table
object store
ext. for internal objects offset

108. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
value
type_info
value
type_info
value
type_info
guards zval
$prop1 zval
$prop2 zval
object store
ext. for internal objects
offset
…
handlers table
offset

109. 7
zend_object *
refcount type_info
handle
ce
handlers
properties
value
type_info
value
type_info
value
type_info
guards zval
$prop1 zval
$prop2 zval
object store
ext. for internal objects
offset
free()
dtor()
clone()
…
handlers table
offset

110. 5
references

111. value = LONG(42)
refcount = 3$i
$j
$k
$i = 42;
$j = $i;
$k = $i;
5

112. value = LONG(42)
refcount = 2$i
$k
$i = 42;
$j = $i;
$k = $i;
$k++;
5
value = LONG(43)
refcount = 1
$j

113. value = LONG(42)
refcount = 2$i
$k
$i = 42;
$j = $i;
$k = $i;
$k++;
5
value = LONG(43)
refcount = 1
$j
copy-on-write (COW)

114. value = LONG(42)
refcount = 3 is_ref = 1$i
$j
$k
$i = 42;
$j =& $i;
$k =& $i;
5

115. value = LONG(43)
refcount = 3 is_ref = 1$i
$j
$k
$i = 42;
$j =& $i;
$k =& $i;
$k++;
5

116. $i = 42;
$j =& $i;
$k =& $i;
7
$i value
REFERENCE
$j value
REFERENCE
$k value
REFERENCE
refcount = 3 type_info
value = 42
LONG
zend_reference

117. $a = range(
0,1000000);
$r =& $a;
7
$a value
REFERENCE
$r value
REFERENCE refcount = 2 type_info
value
ARRAY
zend_reference
refcount = 1 type_info
…
zend_array

118. $a = range(
0,1000000);
$r =& $a;
$v = $a;
7
$a value
REFERENCE
$r value
REFERENCE
$v value
ARRAY
refcount = 2 type_info
value
ARRAY
zend_reference
refcount = 2 type_info
…
zend_array

119. PHP 5 PHP 7
zval 32 bytes 16 bytes
HashTable element 80 bytes 36 bytes (incl. zval)
HashTable 72 bytes 56 bytes
object 96 bytes 40 bytes

120. PHP 5 PHP 7
zval 32 bytes 16 bytes
HashTable element 80 bytes 36 bytes (incl. zval)
HashTable 72 bytes 56 bytes
object 96 bytes 40 bytes
fewer allocations
less indirection

121. PHP 7 Alpha 1
June 11th

122. @nikita_ppv
nikic@php.net