/*BSD爱好者乐园,~6q5r c.q4]k#l
* 设置记录锁子函数lock_set.c
,KBw KG#[-l9W/H
v(F *BSD爱好者乐园,n[e,b[1y;d%D
* 记录锁分为读取锁和写入锁，其中读取锁又称为共享锁，可以使多个
*C.kbI _8f * 进程都能够在文件的同一部分建立读取锁。而写入锁又称为互斥锁，
0U9e&i$F;C'v:fM * 在任何时刻只能有一个进程在文件的某个部分建立写入锁。当然，在
L'},P1?/c/F&K * 文件的同一部分不能同时建立读取锁和写入锁。BSD爱好者乐园S(I2f3bD2v
*BSD爱好者乐园h.N+jd4K-H+^
* fcntl的lock结构如下所示：
RV.q"P9q * struct flock {
8F e e5w*U#G"k_ * short l_type;
SW!v3ox:P Q2IW * off_t l_start;
o R E0b;C/Aq * short l_whence;BSD爱好者乐园 p1J*V6V!f2Ve
* off_t l_len;BSD爱好者乐园,_W7Qa"Y(R
* pid_t l_pid;BSD爱好者乐园)myj.O
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e
* }BSD爱好者乐园e I8n:V$yw
*
9]vh[vu ^"} * 技巧：为加锁整个文件，通常的方法是将l_start说明为0，l_whenceBSD爱好者乐园1m$cv%H[gH
* 说明为SEEK_SET，l_len说明为0。
*G8d
]4Go;F` */
*{h-v
} ~$|;FQ8@)kj$oBSD爱好者乐园t#v-T
|yH.A9IE
#include<stdio.h>
4a)\L4N z Jjt#include<unistd.h>BSD爱好者乐园#@J"Er2Z:e#O F
#include<fcntl.h>
i:pKP z-X{Y2h|^g
$H'P)d g"B1js*^8@)`voidprint_lock(structflock lock)
v*}T6Zs"~k'h{
9o
c9_E9h,x,E;W printf(" -----------------------------\n");
(r@&oW H!^]h
5o0j/z.D1B if(lock.l_type==F_RDLCK){BSD爱好者乐园5I%Vc ^JV K
printf("\tl_type: F_RDLCK\n");
HThG)| }BSD爱好者乐园7WK+r3n(A/X
m'[_rg3g H
elseif(lock.l_type==F_WRLCK){
d:m ~C4K3|;Z$C.lj Z printf("\tl_type: F_WRLCK\n");
c dn%z ]1n A U,Y }BSD爱好者乐园:Y(sP5Mw&_#vN#f
elseif(lock.l_type==F_UNLCK){
1s_ e8~
\ h)f printf("\tl_type: F_UNLCK\n");
iDi[C }
Zi lY*] J&Y-w0kBSD爱好者乐园8js K,s6Q&x`
printf("\tl_start: %d\n",(int)lock.l_start);
&C ?C.D3KT N|
"A'p"BPr1N'z if(lock.l_whence==SEEK_SET){
N]f^!AY9@ uH printf("\tl_whence: SEEK_SET\n");
UURJ
E%` }
!Gl `q0Yn8R elseif(lock.l_whence==SEEK_CUR){BSD爱好者乐园:Ual+f8]
printf("\tl_whence: SEEK_CUR\n");
4N)rJ:}%VwiCn!w }
s*Ue2X,c7X elseif(lock.l_whence==SEEK_END){
;|0d4U:{X@,o printf("\tl_whence: SEEK_END\n");BSD爱好者乐园)`(Z.Y1LN q
}BSD爱好者乐园"J/B9~ J5U(uy&S
BSD爱好者乐园 Kp*P k ]!|A
printf("\tl_len: %d\n",(int)lock.l_len);
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[-bBSD爱好者乐园B8k/D"S;k x:h(C
printf(" -----------------------------\n");BSD爱好者乐园W3d%T5L3u
HH0P&IR:Y
A
}
-B fq z
LXSb
4?V&id7b`voidlock_set(intfd,inttype)BSD爱好者乐园5x
]i0cz D
{BSD爱好者乐园U"^ m)VY Q
structflock lock;BSD爱好者乐园0~ei&Ao#H
BSD爱好者乐园[,r&V t b$]Kic+S+W;z g5R
/*赋值lock结构体，加锁整个文件*/BSD爱好者乐园Ah4u'G K$bS z
lock.l_whence=SEEK_SET;
9_p~\4~2xU'b lock.l_start=0;BSD爱好者乐园!Z-j/o Yp,f
lock.l_len=0;BSD爱好者乐园8U^(k:Uk3{Me a'yC
BSD爱好者乐园}*w(q2hvx4sa
while(1){
a
zxT-TiF I#G Z lock.l_type=type;
i-I\4^ ~*E.f
YrD_%B.O /*
Ub#sa lM * 根据不同的type来给文件加锁或解锁，
/|t3R J U9I.NZ8t[F * 如果成功，则返回0，失败则返回1。BSD爱好者乐园%wp}-_
C2@8X
h4z m-b
* 举例：如果一个文件原来已经建立了互斥锁，那么再调用fcntlBSD爱好者乐园-[2D'gE?uq
* 建立锁就会失败，返回-1。BSD爱好者乐园6K P dsKAu%Km
*/
^B3uq%rL3o0bN if((fcntl(fd,F_SETLK,&lock))==0){
I I7UD"F3~I8o] /*如果是共享锁*/BSD爱好者乐园b-j9px u*v(eG
if(lock.l_type==F_RDLCK){
.q1[NX3Nv printf("read only set by %d\n",getpid());
?pR O-Iz }
2N+z ulmI(e{)O%~-Q /*如果是互斥锁*/BSD爱好者乐园1]!^$[H_:P/@
elseif(lock.l_type==F_WRLCK){BSD爱好者乐园U"b!Q2iT6A$jk
printf("write lock set by %d\n",getpid());BSD爱好者乐园e-eS,Jp sdD
}
V{aVMl A&K elseif(lock.l_type==F_UNLCK){
v u g5C2M'j:]6~wQ printf("release lock by %d\n",getpid());BSD爱好者乐园8BZ xG4e%@3d8W
}
+g1C d5Z:~ j$NZ print_lock(lock);
U,hB#C7O ^/O g return;
amB4J5lUp }BSD爱好者乐园p2D3\1~ bbB
else{
^:j6W
Hw4f jf /*
&I4E5k8u I9M vWB * 获得lock的描述，也就是将文件fd的加锁信息存入到lock结构中BSD爱好者乐园9N Wm
v _ Wkd
* 如果成功则返回0
w;?&\
isW;Y+_(Z * 如果失败则返回-1BSD爱好者乐园 Xy,H$y%P_5w"]
*/BSD爱好者乐园h&vIP'xA f
if((fcntl(fd,F_GETLK,&lock))==0){BSD爱好者乐园a {#Z2R`4RK&b
if(lock.l_type!=F_UNLCK){
(F CPR A&_'P-C2{D if(lock.l_type==F_RDLCK){BSD爱好者乐园 T7E)K2vNO!p
printf("read lock already set by %d\n",lock.l_pid);
oiT5a,oxN"fs }
@2enLr7|$rla elseif(lock.l_type==F_WRLCK){BSD爱好者乐园z/G*Y{ ]'l
printf("write lock already set by %d\n",lock.l_pid);
]B,zR0n{/|To }
.I5k
}"? Cc getchar();BSD爱好者乐园4d
l\
g6iW!h7VVu
}
fu9q@9s7YH }
po D/ws;|(} else{
z(I7qe1h6N e n)} y printf("cannot get the description of struck flock.\n");BSD爱好者乐园T(TYCG+w:A5P
}
`;pk0Z } d2aZwg }
V,c&wu6j }BSD爱好者乐园RR2t? j m4j n3J0T
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