Ric*_*ral 9 c fork pipe exec dup2
这是我的代码:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <wait.h>
#include <readline/readline.h>
#define NUMPIPES 2
int main(int argc, char *argv[]) {
char *bBuffer, *sPtr, *aPtr = NULL, *pipeComms[NUMPIPES], *cmdArgs[10];
int fdPipe[2], pCount, aCount, i, status, lPids[NUMPIPES];
pid_t pid;
pipe(fdPipe);
while(1) {
bBuffer = readline("Shell> ");
if(!strcasecmp(bBuffer, "exit")) {
return 0;
}
sPtr = bBuffer;
pCount = -1;
do {
aPtr = strsep(&sPtr, "|");
pipeComms[++pCount] = aPtr;
} while(aPtr);
for(i = 0; i < pCount; i++) {
aCount = -1;
do {
aPtr = strsep(&pipeComms[i], " ");
cmdArgs[++aCount] = aPtr;
} while(aPtr);
cmdArgs[aCount] = 0;
if(strlen(cmdArgs[0]) > 0) {
pid = fork();
if(pid == 0) {
if(i == 0) {
close(fdPipe[0]);
dup2(fdPipe[1], STDOUT_FILENO);
close(fdPipe[1]);
} else if(i == 1) {
close(fdPipe[1]);
dup2(fdPipe[0], STDIN_FILENO);
close(fdPipe[0]);
}
execvp(cmdArgs[0], cmdArgs);
exit(1);
} else {
lPids[i] = pid;
/*waitpid(pid, &status, 0);
if(WIFEXITED(status)) {
printf("[%d] TERMINATED (Status: %d)\n",
pid, WEXITSTATUS(status));
}*/
}
}
}
for(i = 0; i < pCount; i++) {
waitpid(lPids[i], &status, 0);
if(WIFEXITED(status)) {
printf("[%d] TERMINATED (Status: %d)\n",
lPids[i], WEXITSTATUS(status));
}
}
}
return 0;
}
(代码已更新,以反映下面两个答案提出的更改,它仍然无法正常工作......)
这是失败的测试用例:
nazgulled ~/Projects/SO/G08 $ ls -l
total 8
-rwxr-xr-x 1 nazgulled nazgulled 7181 2009-05-27 17:44 a.out
-rwxr-xr-x 1 nazgulled nazgulled 754 2009-05-27 01:42 data.h
-rwxr-xr-x 1 nazgulled nazgulled 1305 2009-05-27 17:50 main.c
-rwxr-xr-x 1 nazgulled nazgulled 320 2009-05-27 01:42 makefile
-rwxr-xr-x 1 nazgulled nazgulled 14408 2009-05-27 17:21 prog
-rwxr-xr-x 1 nazgulled nazgulled 9276 2009-05-27 17:21 prog.c
-rwxr-xr-x 1 nazgulled nazgulled 10496 2009-05-27 17:21 prog.o
-rwxr-xr-x 1 nazgulled nazgulled 16 2009-05-27 17:19 test
nazgulled ~/Projects/SO/G08 $ ./a.out
Shell> ls -l|grep prog
[4804] TERMINATED (Status: 0)
-rwxr-xr-x 1 nazgulled nazgulled 14408 2009-05-27 17:21 prog
-rwxr-xr-x 1 nazgulled nazgulled 9276 2009-05-27 17:21 prog.c
-rwxr-xr-x 1 nazgulled nazgulled 10496 2009-05-27 17:21 prog.o
问题是我应该在那之后返回我的shell,我应该看到"Shell>"等待更多输入.您还可以注意到,您没有看到类似于"[4804] TERMINATED(状态:0)"的消息(但具有不同的pid),这意味着第二个进程未终止.
我认为这与grep有关,因为这有效:
nazgulled ~/Projects/SO/G08 $ ./a.out
Shell> echo q|sudo fdisk /dev/sda
[4838] TERMINATED (Status: 0)
The number of cylinders for this disk is set to 1305.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Command (m for help):
[4839] TERMINATED (Status: 0)
您可以轻松看到两个"终止"消息......
那么,我的代码出了什么问题？
eph*_*ent 28
即使管道的第一个命令退出(并且关闭stdout=~fdPipe[1]),父级仍然fdPipe[1]打开.
因此,管道的第二个命令stdin=~fdPipe[0]永远不会获得EOF,因为管道的另一个端点仍然是打开的.
您需要pipe(fdPipe)为每个创建一个新的|,并确保关闭父级中的两个端点; 即
for cmd in cmds
if there is a next cmd
pipe(new_fds)
fork
if child
if there is a previous cmd
dup2(old_fds[0], 0)
close(old_fds[0])
close(old_fds[1])
if there is a next cmd
close(new_fds[0])
dup2(new_fds[1], 1)
close(new_fds[1])
exec cmd || die
else
if there is a previous cmd
close(old_fds[0])
close(old_fds[1])
if there is a next cmd
old_fds = new_fds
if there are multiple cmds
close(old_fds[0])
close(old_fds[1])
此外,为了更安全,您应该在执行任何和操作之前处理fdPipe和{STDIN_FILENO,STDOUT_FILENO}重叠的情况.如果有人设法在stdin或stdout关闭的情况下启动shell,可能会发生这种情况,并且会导致与此处的代码混淆.closedup2
fdPipe1 fdPipe3
v v
cmd1 | cmd2 | cmd3 | cmd4 | cmd5
^ ^
fdPipe2 fdPipe4
此外,以确保您关闭该管道的终点在父,我试图让该点fdPipe1,fdPipe2等不能是相同的pipe().
/* suppose stdin and stdout have been closed...
* for example, if your program was started with "./a.out <&- >&-" */
close(0), close(1);
/* then the result you get back from pipe() is {0, 1} or {1, 0}, since
* fd numbers are always allocated from the lowest available */
pipe(fdPipe);
close(0);
dup2(fdPipe[0], 0);
我知道您不会close(0)在现有代码中使用,但最后一段警告您要注意此案例.
您对代码的以下最小更改使其适用于您提到的特定失败案例:
@@ -12,6 +12,4 @@
pid_t pid;
- pipe(fdPipe);
-
while(1) {
bBuffer = readline("Shell> ");
@@ -29,4 +27,6 @@
} while(aPtr);
+ pipe(fdPipe);
+
for(i = 0; i < pCount; i++) {
aCount = -1;
@@ -72,4 +72,7 @@
}
+ close(fdPipe[0]);
+ close(fdPipe[1]);
+
for(i = 0; i < pCount; i++) {
waitpid(lPids[i], &status, 0);
这不适用于管道中的多个命令; 为此,你需要这样的东西:(未经测试,因为你必须修复其他东西)
@@ -9,9 +9,7 @@
int main(int argc, char *argv[]) {
char *bBuffer, *sPtr, *aPtr = NULL, *pipeComms[NUMPIPES], *cmdArgs[10];
- int fdPipe[2], pCount, aCount, i, status, lPids[NUMPIPES];
+ int fdPipe[2], fdPipe2[2], pCount, aCount, i, status, lPids[NUMPIPES];
pid_t pid;
- pipe(fdPipe);
-
while(1) {
bBuffer = readline("Shell> ");
@@ -32,4 +30,7 @@
aCount = -1;
+ if (i + 1 < pCount)
+ pipe(fdPipe2);
+
do {
aPtr = strsep(&pipeComms[i], " ");
@@ -43,11 +44,12 @@
if(pid == 0) {
- if(i == 0) {
- close(fdPipe[0]);
+ if(i + 1 < pCount) {
+ close(fdPipe2[0]);
- dup2(fdPipe[1], STDOUT_FILENO);
+ dup2(fdPipe2[1], STDOUT_FILENO);
- close(fdPipe[1]);
- } else if(i == 1) {
+ close(fdPipe2[1]);
+ }
+ if(i != 0) {
close(fdPipe[1]);
@@ -70,4 +72,17 @@
}
}
+
+ if (i != 0) {
+ close(fdPipe[0]);
+ close(fdPipe[1]);
+ }
+
+ fdPipe[0] = fdPipe2[0];
+ fdPipe[1] = fdPipe2[1];
+ }
+
+ if (pCount) {
+ close(fdPipe[0]);
+ close(fdPipe[1]);
}