C、fork()中的一些语句没有执行
C, Some statements in fork() not executing
我想我了解 fork() 的工作原理，但我在正文中只执行了一些语句。例如，在每个转换块中，所有 printf() 都将执行，但 png_count、gif_count 和 bmp_count 永远不会递增并保持为 0（如 printf() 输出中所示对于 child(x);
/* Create Processes */
printf("\n+++++++++++CREATING PROCESSES+++++++++++\n");
int i, pid;
png_count = 0;
gif_count = 0;
bmp_count = 0;
for(i = 0; i < convert_count; i++) {
pid = fork();
if(pid < 0) {
printf("Error: fork failed");
exit(1);
}
else if (pid == 0) {
/* Child execution */
/* PNG conversion */
if ((getpid() % 2) == 0) {
image_in_path = getInPath(input_dir, png_images[png_count]);
image_out_path = getOutPath(output_dir, png_images[png_count]);
printf("image_in_path: %s\n", image_in_path);
printf("Child (%d): %d\n", png_count+1, getpid());
png_count++;
printf("Converting: %s\n", image_in_path);
execlp("convert", "convert", image_in_path, "-resize", "200x200", image_out_path, NULL);
exit(1);
}
/* GIF conversion */
else if ((getpid() % 3) == 0) {
image_in_path = getInPath(input_dir, gif_images[gif_count]);
image_out_path = getOutPath(output_dir, gif_images[gif_count]);
printf("image_in_path: %s\n", image_in_path);
printf("Child (%d): %d\n", gif_count+1, getpid());
gif_count++;
printf("Converting: %s\n", image_in_path);
execlp("convert", "convert", image_in_path, "-resize", "200x200", image_out_path, NULL);
exit(1);
}
/* BMP conversion */
else {
image_in_path = getInPath(input_dir, bmp_images[bmp_count]);
image_out_path = getOutPath(output_dir, bmp_images[bmp_count]);
printf("image_in_path: %s\n", image_in_path);
printf("Child (%d): %d\n", bmp_count+1, getpid());
bmp_count++;
printf("Converting: %s\n", image_in_path);
execlp("convert", "convert", image_in_path, "-resize", "200x200", image_out_path, NULL);
exit(1);
}
}
else {
/* Parent Execution */
wait(NULL);
}
}
输出：
+++++++++++CREATING PROCESSES+++++++++++
image_in_path: idir/panda.bmp
Child (1): 5389
Converting: idir/panda.bmp
image_in_path: idir/panda.bmp
Child (1): 5393
Converting: idir/panda.bmp
image_in_path: idir/penguin.gif
Child (1): 5397
Converting: idir/penguin.gif
image_in_path: idir/bmp.png
Child (1): 5402
Converting: idir/bmp.png
image_in_path: idir/bmp.png
Child (1): 5408
Converting: idir/bmp.png
image_in_path: idir/panda.bmp
Child (1): 5413
Converting: idir/panda.bmp
image_in_path: idir/panda.bmp
Child (1): 5417
Converting: idir/panda.bmp
image_in_path: idir/penguin.gif
Child (1): 5421
Converting: idir/penguin.gif
image_in_path: idir/panda.bmp
Child (1): 5425
Converting: idir/panda.bmp
image_in_path: idir/panda.bmp
Child (1): 5429
Converting: idir/panda.bmp
在此先感谢您的帮助！我花了太多时间试图解决这个问题，但运气不佳。
分叉的子进程获得父进程内存的副本（并与其父进程和兄弟进程共享大多数打开的文件描述符）。
他们不是所有共享相同的内存，因此子项中的变量更改不会对父项或子项产生影响兄弟。
为了获得我认为您想要的效果，您需要在每次 fork() 之前对父项进行更改，然后让子项根据看到的变量执行操作。
a programmer should always be very familiar with the system functions they call in their code.
the main thing to notice is a child gets a COPY of the parents data, not access to the actual data.
here is a copy of the 'man fork' output.
FORK(2) Linux 程序员手册 FORK(2)
姓名
fork - 创建一个 child 进程
概要
#include
pid_t fork(void);
说明
fork() 通过复制调用进程来创建一个新进程。这
新进程，称为 child，是
调用过程，简称parent，除以下情况外
积分：
* The child has its own unique process ID, and this PID does not match
the ID of any existing process group (setpgid(2)).
* The child's parent process ID is the same as the parent's process
ID.
* The child does not inherit its parent's memory locks (mlock(2),
mlockall(2)).
* Process resource utilizations (getrusage(2)) and CPU time counters
(times(2)) are reset to zero in the child.
* The child's set of pending signals is initially empty (sigpend‐
ing(2)).
* The child does not inherit semaphore adjustments from its parent
(semop(2)).
* The child does not inherit record locks from its parent (fcntl(2)).
* The child does not inherit timers from its parent (setitimer(2),
alarm(2), timer_create(2)).
* The child does not inherit outstanding asynchronous I/O operations
from its parent (aio_read(3), aio_write(3)), nor does it inherit any
asynchronous I/O contexts from its parent (seeio_setup(2)).
The process attributes in the preceding list are all specified in
POSIX.1-2001. The parent and child also differ with respect to the
following Linux-specific process attributes:
* The child does not inherit directory change notifications (dnotify)
from its parent (see the description of F_NOTIFY in fcntl(2)).
* The prctl(2) PR_SET_PDEATHSIG setting is reset so that the child
does not receive a signal when its parent terminates.
* Memory mappings that have been marked with the madvise(2) MADV_DONT‐
FORK flag are not inherited across a fork().
* The termination signal of the child is always SIGCHLD (see
clone(2)).
Note the following further points:
* The child process is created with a single thread — the one that
called fork(). The entire virtual address space of the parent is
replicated in the child, including the states of mutexes, condition
variables, and other pthreads objects; the use of pthread_atfork(3)
may be helpful for dealing with problems that this can cause.
* The child inherits copies of the parent's set of open file descrip‐
tors. Each file descriptor in the child refers to the same open
file description (see open(2)) as the corresponding file descriptor
in the parent. This means that the two descriptors share open file
status flags, current file offset, and signal-driven I/O attributes
(see the description of F_SETOWN and F_SETSIG in fcntl(2)).
* The child inherits copies of the parent's set of open message queue
descriptors (see mq_overview(7)). Each descriptor in the child
refers to the same open message queue description as the correspond‐
ing descriptor in the parent. This means that the two descriptors
share the same flags (mq_flags).
* The child inherits copies of the parent's set of open directory
streams (see opendir(3)). POSIX.1-2001 says that the corresponding
directory streams in the parent and child may share the directory
stream positioning; on Linux/glibc they do not.
RETURN 值
成功时，child 进程的 PID 在 parent 中返回，并且
child 中返回 0。失败时，在 parent 中返回 -1，
没有 child 进程被创建，errno 被适当地设置。
错误
EAGAIN fork() 无法分配足够的内存来复制 parent 的
页表并为 child.
分配一个任务结构
EAGAIN It was not possible to create a new process because the caller's
RLIMIT_NPROC resource limit was encountered. To exceed this
limit, the process must have either the CAP_SYS_ADMIN or the
CAP_SYS_RESOURCE capability.
ENOMEM fork() failed to allocate the necessary kernel structures
because memory is tight.
符合
SVr4, 4.3BSD, POSIX.1-2001.
注意事项
在 Linux 下，fork() 是使用 copy-on-write 页实现的，因此
它招致的唯一惩罚是复制所需的时间和内存。
整理 parent 的页表，并创建一个独特的任务结构
对于 child.
Since version 2.3.3, rather than invoking the kernel's fork() system
call, the glibc fork() wrapper that is provided as part of the NPTL
threading implementation invokes clone(2) with flags that provide the
same effect as the traditional system call. The glibc wrapper invokes
any fork handlers that have been established using pthread_atfork(3).
示例
参见 pipe(2) 和 wait(2)。
另见
clone(2), execve(2), setrlimit(2), unshare(2), vfork(2), wait(2), dae-
mon(3), capabilities(7), credentials(7)
版画
此页面是 Linux man-pages 项目 3.23 版的一部分。一种
项目的描述，以及关于报告错误的信息，可以
在 http://www.kernel.org/doc/man-pages/.
找到
Linux 2009-04-27 分叉(2)
我想我了解 fork() 的工作原理，但我在正文中只执行了一些语句。例如，在每个转换块中，所有 printf() 都将执行，但 png_count、gif_count 和 bmp_count 永远不会递增并保持为 0（如 printf() 输出中所示对于 child(x);
/* Create Processes */
printf("\n+++++++++++CREATING PROCESSES+++++++++++\n");
int i, pid;
png_count = 0;
gif_count = 0;
bmp_count = 0;
for(i = 0; i < convert_count; i++) {
pid = fork();
if(pid < 0) {
printf("Error: fork failed");
exit(1);
}
else if (pid == 0) {
/* Child execution */
/* PNG conversion */
if ((getpid() % 2) == 0) {
image_in_path = getInPath(input_dir, png_images[png_count]);
image_out_path = getOutPath(output_dir, png_images[png_count]);
printf("image_in_path: %s\n", image_in_path);
printf("Child (%d): %d\n", png_count+1, getpid());
png_count++;
printf("Converting: %s\n", image_in_path);
execlp("convert", "convert", image_in_path, "-resize", "200x200", image_out_path, NULL);
exit(1);
}
/* GIF conversion */
else if ((getpid() % 3) == 0) {
image_in_path = getInPath(input_dir, gif_images[gif_count]);
image_out_path = getOutPath(output_dir, gif_images[gif_count]);
printf("image_in_path: %s\n", image_in_path);
printf("Child (%d): %d\n", gif_count+1, getpid());
gif_count++;
printf("Converting: %s\n", image_in_path);
execlp("convert", "convert", image_in_path, "-resize", "200x200", image_out_path, NULL);
exit(1);
}
/* BMP conversion */
else {
image_in_path = getInPath(input_dir, bmp_images[bmp_count]);
image_out_path = getOutPath(output_dir, bmp_images[bmp_count]);
printf("image_in_path: %s\n", image_in_path);
printf("Child (%d): %d\n", bmp_count+1, getpid());
bmp_count++;
printf("Converting: %s\n", image_in_path);
execlp("convert", "convert", image_in_path, "-resize", "200x200", image_out_path, NULL);
exit(1);
}
}
else {
/* Parent Execution */
wait(NULL);
}
}
输出：
+++++++++++CREATING PROCESSES+++++++++++
image_in_path: idir/panda.bmp
Child (1): 5389
Converting: idir/panda.bmp
image_in_path: idir/panda.bmp
Child (1): 5393
Converting: idir/panda.bmp
image_in_path: idir/penguin.gif
Child (1): 5397
Converting: idir/penguin.gif
image_in_path: idir/bmp.png
Child (1): 5402
Converting: idir/bmp.png
image_in_path: idir/bmp.png
Child (1): 5408
Converting: idir/bmp.png
image_in_path: idir/panda.bmp
Child (1): 5413
Converting: idir/panda.bmp
image_in_path: idir/panda.bmp
Child (1): 5417
Converting: idir/panda.bmp
image_in_path: idir/penguin.gif
Child (1): 5421
Converting: idir/penguin.gif
image_in_path: idir/panda.bmp
Child (1): 5425
Converting: idir/panda.bmp
image_in_path: idir/panda.bmp
Child (1): 5429
Converting: idir/panda.bmp
在此先感谢您的帮助！我花了太多时间试图解决这个问题，但运气不佳。
分叉的子进程获得父进程内存的副本（并与其父进程和兄弟进程共享大多数打开的文件描述符）。
他们不是所有共享相同的内存，因此子项中的变量更改不会对父项或子项产生影响兄弟。
为了获得我认为您想要的效果，您需要在每次 fork() 之前对父项进行更改，然后让子项根据看到的变量执行操作。
a programmer should always be very familiar with the system functions they call in their code.
the main thing to notice is a child gets a COPY of the parents data, not access to the actual data.
here is a copy of the 'man fork' output.
FORK(2) Linux 程序员手册 FORK(2)
姓名 fork - 创建一个 child 进程
概要 #include
pid_t fork(void);
说明 fork() 通过复制调用进程来创建一个新进程。这 新进程，称为 child，是 调用过程，简称parent，除以下情况外 积分：
* The child has its own unique process ID, and this PID does not match
the ID of any existing process group (setpgid(2)).
* The child's parent process ID is the same as the parent's process
ID.
* The child does not inherit its parent's memory locks (mlock(2),
mlockall(2)).
* Process resource utilizations (getrusage(2)) and CPU time counters
(times(2)) are reset to zero in the child.
* The child's set of pending signals is initially empty (sigpend‐
ing(2)).
* The child does not inherit semaphore adjustments from its parent
(semop(2)).
* The child does not inherit record locks from its parent (fcntl(2)).
* The child does not inherit timers from its parent (setitimer(2),
alarm(2), timer_create(2)).
* The child does not inherit outstanding asynchronous I/O operations
from its parent (aio_read(3), aio_write(3)), nor does it inherit any
asynchronous I/O contexts from its parent (seeio_setup(2)).
The process attributes in the preceding list are all specified in
POSIX.1-2001. The parent and child also differ with respect to the
following Linux-specific process attributes:
* The child does not inherit directory change notifications (dnotify)
from its parent (see the description of F_NOTIFY in fcntl(2)).
* The prctl(2) PR_SET_PDEATHSIG setting is reset so that the child
does not receive a signal when its parent terminates.
* Memory mappings that have been marked with the madvise(2) MADV_DONT‐
FORK flag are not inherited across a fork().
* The termination signal of the child is always SIGCHLD (see
clone(2)).
Note the following further points:
* The child process is created with a single thread — the one that
called fork(). The entire virtual address space of the parent is
replicated in the child, including the states of mutexes, condition
variables, and other pthreads objects; the use of pthread_atfork(3)
may be helpful for dealing with problems that this can cause.
* The child inherits copies of the parent's set of open file descrip‐
tors. Each file descriptor in the child refers to the same open
file description (see open(2)) as the corresponding file descriptor
in the parent. This means that the two descriptors share open file
status flags, current file offset, and signal-driven I/O attributes
(see the description of F_SETOWN and F_SETSIG in fcntl(2)).
* The child inherits copies of the parent's set of open message queue
descriptors (see mq_overview(7)). Each descriptor in the child
refers to the same open message queue description as the correspond‐
ing descriptor in the parent. This means that the two descriptors
share the same flags (mq_flags).
* The child inherits copies of the parent's set of open directory
streams (see opendir(3)). POSIX.1-2001 says that the corresponding
directory streams in the parent and child may share the directory
stream positioning; on Linux/glibc they do not.
RETURN 值 成功时，child 进程的 PID 在 parent 中返回，并且 child 中返回 0。失败时，在 parent 中返回 -1， 没有 child 进程被创建，errno 被适当地设置。
错误 EAGAIN fork() 无法分配足够的内存来复制 parent 的 页表并为 child.
分配一个任务结构 EAGAIN It was not possible to create a new process because the caller's
RLIMIT_NPROC resource limit was encountered. To exceed this
limit, the process must have either the CAP_SYS_ADMIN or the
CAP_SYS_RESOURCE capability.
ENOMEM fork() failed to allocate the necessary kernel structures
because memory is tight.
符合 SVr4, 4.3BSD, POSIX.1-2001.
注意事项 在 Linux 下，fork() 是使用 copy-on-write 页实现的，因此 它招致的唯一惩罚是复制所需的时间和内存。 整理 parent 的页表，并创建一个独特的任务结构 对于 child.
Since version 2.3.3, rather than invoking the kernel's fork() system
call, the glibc fork() wrapper that is provided as part of the NPTL
threading implementation invokes clone(2) with flags that provide the
same effect as the traditional system call. The glibc wrapper invokes
any fork handlers that have been established using pthread_atfork(3).
示例 参见 pipe(2) 和 wait(2)。
另见 clone(2), execve(2), setrlimit(2), unshare(2), vfork(2), wait(2), dae- mon(3), capabilities(7), credentials(7)
版画 此页面是 Linux man-pages 项目 3.23 版的一部分。一种 项目的描述，以及关于报告错误的信息，可以 在 http://www.kernel.org/doc/man-pages/.
找到Linux 2009-04-27 分叉(2)