设T1，T2是两个事务如下：
T1：
A
:
=
A
+
2
，
B
=
B
×
2
A:=A+2，B=Btimes2
A:=A+2，B=B×2;
T2：
A
:
=
A
×
2
，
B
=
B
+
2
A:=Atimes2，B=B+2
A:=A×2，B=B+2;
设A,B的初值都为0
（1）若这两个事务容许并发执行，则有多少种可能的正确结果？请一一例举出来；
有两种可能：
T1 T2 ——
A
=
4
,
B
=
2
A=4,B=2
A=4,B=2
T2 T1 ——
A
=
2
,
B
=
4
A=2,B=4
A=2,B=4
（2）请给出一个可串行化的调度，并给出执行结果；
| T1 | T2 |
|---|---|
| SlockA | |
| Y=Read(A)=0 | |
| Unlock A | |
| Xlock A | |
| A=Y+2 | |
| Write(A) | |
| Unlock A | |
| SlockB | |
| Z=Read(B)=0 | |
| Unlock B | |
| Xlock B | |
| B=Z*2 | |
| Write(B) | |
| Unlock B | |
| SlockA | |
| Y=Read(A)=0 | |
| Unlock A | |
| Xlock A | |
| A=Y*2 | |
| Write(A) | |
| Unlock A | |
| SlockB | |
| Z=Read(B)=0 | |
| Unlock B | |
| Xlock B | |
| B=Z+2 | |
| Write(B) | |
| Unlock B |
结果： A = 4 , B = 2 A=4,B=2 A=4,B=2
（3）请给出一个非串行化的调度，并给出执行结果；
| T1 | T2 |
|---|---|
| SlockA | |
| Y=Read(A)=0 | |
| Unlock A | |
| Xlock A | |
| SlockA | |
| A=Y+2 | 等待 |
| Write(A) | 等待 |
| Unlock A | 等待 |
| Y=Read(A)=0 | |
| Unlock A | |
| Xlock A | |
| SlockB | |
| 等待 | A=Y*2 |
| 等待 | Write(A) |
| 等待 | Unlock A |
| Z=Read(B)=0 | |
| Unlock B | |
| Xlock B | |
| SlockB | |
| B=Z*2 | 等待 |
| Write(B) | 等待 |
| Unlock B | 等待 |
| Z=Read(B)=0 | |
| Unlock B | |
| Xlock B | |
| B=Z+2 | |
| Write(B) | |
| Unlock B |
结果： A = 0 , B = 2 A=0,B=2 A=0,B=2
（4）若这两个事务都遵守两段锁协议，请给出一个不产生死锁的可串行化的调度；
| T1 | T2 |
|---|---|
| SlockA | |
| Y=Read(A)=0 | |
| Xlock A | |
| A=Y+2 | |
| Write(A) | |
| SlockB | |
| Z=Read(B)=0 | |
| Xlock B | |
| B=Z*2 | |
| Write(B) | |
| Unlock A | |
| Unlock A | |
| Unlock B | |
| Unlock B | |
| SlockA | |
| Y=Read(A)=0 | |
| Xlock A | |
| A=Y*2 | |
| Write(A) | |
| SlockB | |
| Z=Read(B)=0 | |
| Xlock B | |
| B=Z+2 | |
| Write(B) | |
| Unlock A | |
| Unlock A | |
| Unlock B | |
| Unlock B |
（5）若这两个事务都遵守两段锁协议，请给出一个产生死锁的可串行化的调度；
| T1 | T2 |
|---|---|
| SlockA | |
| SlockA | |
| Xlock A | |
| 等待 | |
| 等待 | Xlock A |
| 等待 | 等待 |
