Linux 从 C 代码获取当前使用的文件描述符的计数
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Getting count of current used file descriptors from C code
提问by Vivek Goel
Is there a C API to get the:
是否有 C API 来获取：
- Current used file descriptors system wide
- Current used file descriptors of the current process
- 当前使用的文件描述符系统范围
- 当前进程的当前使用的文件描述符
采纳答案by R.. GitHub STOP HELPING ICE
For the current process count, you can use getrlimitto get the file descriptor limit, then iterate over all integers from 0 to that limit and try calling fcntlwith the F_GETFDcommand. It will succeed only on the file descriptors which are actually open, letting you count them.
对于当前进程计数，您可以使用getrlimit获取文件描述符限制，然后遍历从 0 到该限制的所有整数，并尝试fcntl使用F_GETFD命令进行调用。它只会在实际打开的文件描述符上成功，让您计算它们。
Edit:I now have a better way to do it. After getting the rlimit, make a large array of struct pollfd(as large as the limit if possible; otherwise you can break it down into multiple runs/calls) with each fd in the range and the eventsmember set to 0. Call pollon the array with 0 timeout, and look for the POLLNVALflag in the reventsfor each member. This will tell you which among a potentially-huge set of fds are invalid with a single syscall, rather than one syscall per fd.
编辑：我现在有更好的方法来做到这一点。获得 后，使用范围内的每个 fd 和成员设置为 0rlimit制作一个大数组struct pollfd（如果可能，尽可能大；否则您可以将其分解为多次运行/调用）。events调用poll数组时超时为 0 ，并POLLNVAL在revents每个成员的 中查找标志。这将告诉您在单个系统调用中，潜在的大量 fd 中哪些无效，而不是每个 fd 一个系统调用。
回答by Some programmer dude
Since you say you are on Linux, you can open the folder /proc/self/fd/which should contain symbolic links to all open file descriptors.
既然你说你在 Linux 上，你可以打开文件夹/proc/self/fd/，该文件夹应该包含所有打开的文件描述符的符号链接。
回答by Polynomial
You can read /proc/sys/fs/file-nrto find the total number of allocated and free file system handles as well as the maximum allowed.
您可以阅读/proc/sys/fs/file-nr以查找已分配和可用文件系统句柄的总数以及允许的最大值。
[root@box proc]# cat /proc/sys/fs/file-nr
3853 908 53182
| | |
| | |
| | max: maximum open file descriptors
| free: total free allocated file descriptors
allocated: total allocated file descriptors since boot
To calculate the number that are currently in use, just do allocated - free. You could also calculate a percentage of used descriptors by doing ((allocated - free) / max) * 100
要计算当前使用的数量，只需执行allocated - free。您还可以通过执行以下操作来计算已使用描述符的百分比((allocated - free) / max) * 100
As for per-process, I'm not sure of any programmatic way you can do it.
至于每个进程，我不确定您可以使用任何编程方式。
Here's a tutorial on how to do it with lsofanyway: http://linuxshellaccount.blogspot.com/2008/06/finding-number-of-open-file-descriptors.html
这是一个关于如何使用的教程lsof：http: //linuxshellaccount.blogspot.com/2008/06/finding-number-of-open-file-descriptors.html
回答by MD XF
I'm not positive about file descriptors, but you can easily check <stdio.h>files.
我还不能肯定有关文件的描述，但你可以很容易地检查<stdio.h>文件。
In stdio.h, __sF, is a file array that stores every FILE. (googling __sFshows many stdios with a matching keyword).
在stdio.h, __sF, 是一个文件数组，它存储每个FILE. （谷歌搜索__sF显示许多stdio具有匹配关键字的 s）。
If a FILE's flags are empty, the file is not in use. Therefore, we can simply walk through __sF, checking the flag of each FILEin the array.
如果 aFILE的标志为空，则该文件未在使用中。因此，我们可以简单地遍历__sF，检查FILE数组中每个的标志。
#include <stdio.h>
int getOpenFileCount(void)
{
int fileCount;
for (fileCount = 0; __sF[fileCount]._flags != 0; fileCount++)
continue;
return fileCount;
}
