c语言显示系统资源,C语言系统资源控制

小咪咪 2022-10-15 15:55 184阅读 0赞

每一个进程都有自己的一组资源限制，在(\*)inux系统中我们可以通过

\#include int getrlimit(int resource, struct rlimit \*rlim);

int setrlimit(int resource, const struct rlimit \*rlim);

这2个API来取得和设置资源

getrlimit用来取得setrlimit用来设置 这二个参数都需要一个要控制的资源 比如控制CPU、内存、文件描述符个数等等的控制，作为第一个参数传入，第二个参数是一个rlimit的结构体地址(指针)，他的结构如下定义：

定义放在头文件/usr/include/bits/resource.h中

struct rlimit

/\* The current (soft) limit.       \*/

rlim\_t rlim\_cur;

/\* The hard limit.       \*/

rlim\_t rlim\_max;

\};

结构体中 rlim\_cur是要取得或设置的资源软限制的值，rlim\_max是硬限制

这两个值的设置有一个小的约束：

1) 任何进程可以将软限制改为小于或等于硬限制

2) 任何进程都可以将硬限制降低，但普通用户降低了就无法提高，该值必须等于或大于软限制

3) 只有超级用户可以提高硬限制

一个无限的限制由常量RLIM\_INFINITY指定(The       value       RLIM\_INFINITY       denotes no limit on a resource )

RLIMIT\_AS

The       maximum       size       of       the       process鈙       virtual memory (address

space) in bytes.       This limit affects calls to       brk(2),       mmap(2)

and       mremap(2), which fail with the error ENOMEM upon exceeding

this limit. Also automatic stack expansion will fail (and       gen-

erate       a SIGSEGV that kills the process when no alternate stack

has been made available).        Since       the       value       is       a       long,       on

machines with a 32-bit long either this limit is at most 2 GiB,

or this resource is unlimited.

RLIMIT\_CORE

Maximum size of core file. When 0 no core dump files       are       cre-

ated.       When nonzero, larger dumps are truncated to this size.设定最大的core文件，当值为0时将禁止core文件非0时将设定产生的最大core文件大小为设定的值

RLIMIT\_CPU                   CPU       time       limit in seconds.       When the process reaches the soft

limit, it is sent a SIGXCPU signal.        The       default       action       for

this       signal       is to terminate the process.       However, the signal

can be caught, and the handler can return control to       the       main

program.       If the process continues to consume CPU time, it will

be sent SIGXCPU       once       per       second       until       the       hard       limit       is

reached,       at which time it is sent SIGKILL.       (This latter point

describes Linux 2.2 and 2.4 behaviour.       Implementations vary in

how       they       treat       processes       which continue to consume CPU time

after reaching the soft limit.       Portable applications that need

to catch this signal should perform an orderly termination upon

first receipt of SIGXCPU.)CPU时间的最大量值(秒)，当超过此软限制时向该进程发送SIGXCPU信号

RLIMIT\_DATA

The maximum size of the       process鈙       data       segment       (initialized

data,       uninitialized data, and heap).       This limit affects calls

to brk() and sbrk(), which fail       with       the       error       ENOMEM       upon

encountering the soft limit of this resource.数据段的最大字节长度

RLIMIT\_FSIZE                   The       maximum       size       of       files       that       the       process       may       create.

Attempts to extend a file beyond this limit result in       delivery

of a SIGXFSZ signal.       By default, this signal terminates a pro-

cess, but a process can catch this       signal       instead,       in       which

case the relevant system call (e.g., write(), truncate()) fails

with the error EFBIG.可以创建的文件的最大字节长度，当超过此软限制时向进程发送SIGXFSZ

RLIMIT\_MEMLOCK

The maximum number of bytes       of       virtual       memory       that       may       be

locked into RAM using mlock() and mlockall().

RLIMIT\_NOFILE

Specifies       a value one greater than the maximum file descriptor

number that can be opened by this process.        Attempts       (open(),

pipe(),       dup(),       etc.)        to       exceed       this limit yield the error

EMFILE.每个进程能够打开的最多文件数。更改此限制将影响到sysconf函数在参数\_SC\_CHILD\_MAX中的返回值

RLIMIT\_OFILE is the BSD name for RLIMIT\_NOFILE.

这里BSD系统中RLIMIT\_NOFILE的别名

RLIMIT\_NPROC

The maximum number of processes that can       be       created       for       the

real       user       ID       of the calling process.       Upon encountering this

limit, fork() fails with the error EAGAIN.每个实际用户ID所拥有的最大子进程数，更改此限制将影响到sysconf函数在参数\_SC\_CHILD\_MAX中返回的值

RLIMIT\_RSS

Specifies the limit (in pages) of the       process鈙       resident       set

(the number of virtual pages resident in RAM).       This limit only

has effect in Linux 2.4 onwatrds, and there only affects       calls

to madvise() specifying MADVISE\_WILLNEED.最大驻内存集字节长度(RSS)如果物理存储器供不应求则内核将从进程处取回超过RSS的部份

RLIMIT\_STACK

The maximum size of the process stack, in bytes.       Upon reaching

this limit, a SIGSEGV signal is generated.       To handle this sig-

nal,       a       process must employ an alternate signal stack (sigalt-

stack(2)).栈的最大长度

RLIMIT——VMEM 可映照地址空间的最大字节长茺，这影响到mmap函数这些限制影响到调用进程并由子进程继承！ 可以在SHELL中预设这些值ulimit命令设置

小试牛刀(代码只是演示，并没有作错误处理)

\#include \#include \#include \#include \#include \#include \#include int main(void)

struct rlimit r;

if(getrlimit(RLIMIT\_NOFILE,&r)<0)

fprintf(stderr,"getrlimit error\\n");

exit(1);

printf("RLIMIT\_NOFILE cur:%d\\n",r.rlim\_cur);

printf("RLIMIT\_NOFILE max:%d\\n",r.rlim\_max);

c语言显示系统资源,C语言系统资源控制

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