q********y
发帖数: 162 | 1 public class Foo
{
private const int SyncLock = 1 << 10;
public void Execute()
{
lock((object)SyncLock)
{
//complex logic
}
}
} | k**********g
发帖数: 989 | 2
SyncLock is a primitive value. Strictly speaking, it is not even a value,
because it is a compile time constant. If you load this value into a CPU
register, the generated code will just write the constant 1024. No memory
loads.
When you do a ((object)SyncLock), this is called boxing. Boxing creates a
new object on the heap, with enough space for storing a copy of the value.
so, it is roughly similar to this in C++ :
struct BoxedInteger { int value; }
BoxedInteger* pObject = new BoxedInteger;
pObject->value = 1024;
Every time the code is entered, it will create a new boxed object. Thus,
each call locks a different object. There is no synchronization, and
therefore multiple threads will enter the complex logic at the same time.
【在 q********y 的大作中提到】
: public class Foo
: {
: private const int SyncLock = 1 << 10;
: public void Execute()
: {
: lock((object)SyncLock)
: {
: //complex logic
: }
: }
| f*******t
发帖数: 7549 | 3 这种错误在java里比较常见
★ 发自iPhone App: ChineseWeb 7.8
【在 k**********g 的大作中提到】
:
: SyncLock is a primitive value. Strictly speaking, it is not even a value,
: because it is a compile time constant. If you load this value into a CPU
: register, the generated code will just write the constant 1024. No memory
: loads.
: When you do a ((object)SyncLock), this is called boxing. Boxing creates a
: new object on the heap, with enough space for storing a copy of the value.
: so, it is roughly similar to this in C++ :
: struct BoxedInteger { int value; }
: BoxedInteger* pObject = new BoxedInteger;
| q********y
发帖数: 162 | 4 Thanks!
【在 k**********g 的大作中提到】
:
: SyncLock is a primitive value. Strictly speaking, it is not even a value,
: because it is a compile time constant. If you load this value into a CPU
: register, the generated code will just write the constant 1024. No memory
: loads.
: When you do a ((object)SyncLock), this is called boxing. Boxing creates a
: new object on the heap, with enough space for storing a copy of the value.
: so, it is roughly similar to this in C++ :
: struct BoxedInteger { int value; }
: BoxedInteger* pObject = new BoxedInteger;
| m*******l
发帖数: 12782 | 5 C# 和 Java 的boxing, unboxing确实和C++相比比较烦
【在 f*******t 的大作中提到】
: 这种错误在java里比较常见
:
: ★ 发自iPhone App: ChineseWeb 7.8
| g*****g
发帖数: 34805 | 6 Java has an object pool between -128 and 127 and it's actually OK to lock in
this range. But it's been well know not to lock on any primitive.
【在 f*******t 的大作中提到】
: 这种错误在java里比较常见
:
: ★ 发自iPhone App: ChineseWeb 7.8
|
|
