顧名思義，不安全的類。
通過這個類可以手動操控記憶體、執行緒，如果使用不當，會造成記憶體洩露，甚至jvm崩潰。
獲取unsafe
unsafe的構造器是私有的，無法通過new來獲得unsafe物件。
可以通過反射來獲取。
field unsafefield = unsafe.
class
.getdeclaredfield
("theunsafe"
);
unsafefield.
setaccessible
(true
);
unsafe unsafe =
(unsafe) unsafefield.
get(null)
;
// allocate memory
long address = unsafe.
allocatememory
(8l)
;// put value
unsafe.
putint
(address,10)
;int num = unsafe.
getint
(address)
;
system.out.
println
(num)
;// free
unsafe.
freememory
(address)
;system.out.
println
(unsafe.
getaddress
(address)
);
thread thread =
newthread((
)->
);
thread.
start()
;
timeunit.milliseconds.
sleep
(1l)
;// 恢復
unsafe.
unpark
(thread)
;
data data =
newdata()
;data.
setid(1
);
data.
setage(2
);
field id = data.
getclass()
.getdeclaredfield
("id");
// get field offset
long fieldoffset = unsafe.
objectfieldoffset
(id)
;
id.setaccessible
(true
);
unsafe.
compareandswaplong
(data,fieldoffset,
1l,5l)
;
system.out.
println
(data.
getid()
);
data[
] datas =
newdata[3
];datas[0]
=new
data
(6l)
;datas[1]
=new
data
(7l)
;datas[2]
=new
data
(8l)
;int baseoffset = unsafe.
arraybaseoffset
(data.
class);
int indexscale = unsafe.
arrayindexscale
(data.
class);
// 獲取第三個元素
object object = unsafe.
getobject
(datas, baseoffset+
(indexscale *2)
);system.out.
println((
(data)object)
.getid()
);// 修改 第二個元素
unsafe.
putobject
(datas,baseoffset+
(indexscale *1)
,new
data
(999l)
);
data o =
(data)unsafe.
allocateinstance
(data.
class);
o.setid
(98798l)
;system.out.
println
(o.getid()
);field field = o.
getclass()
.getdeclaredfield
("id");
field.
setaccessible
(true);
long offset = unsafe.
objectfieldoffset
(field)
;long oldvalue = unsafe.
getandsetlong
(o, offset,
999l)
;unsafe.
putlong
(o,offset,
99999l)
;unsafe.
getandaddlong
(o,offset,1)
;system.out.
println
(o.getid()
);
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