netdata：获取系统最多能够创建多少线程数

小鱼儿 2023-01-02 05:25 126阅读 0赞

# shell #

$ cat /proc/sys/kernel/pid_max    #查看系统支持的最大线程数
    131072

# c代码 #

#include <stdio.h>
    #include <fcntl.h>
    #include <zconf.h>
    
    #define likely(x)  __builtin_expect((x), 1)
    #define unlikely(x)  __builtin_expect((x), 0)
    static inline int read_single_number_file(const char *filename, unsigned long long *result);
    static inline int read_file(const char *filename, char *buffer, size_t size);
    static inline unsigned long long str2ull(const char *s);
    
    pid_t pid_max = 32768;
    pid_t get_system_pid_max(void) {
        
        static char read = 0;
        if(read) return pid_max;
        read = 1;
    
        char filename[FILENAME_MAX + 1];
        snprintf(filename, FILENAME_MAX, "/proc/sys/kernel/pid_max");
    
        unsigned long long max = 0;
        if(read_single_number_file(filename, &max) != 0) {
        
            printf("Cannot open file '%s'. Assuming system supports %d pids.", filename, pid_max);
            return pid_max;
        }
    
        if(!max) {
        
            printf("Cannot parse file '%s'. Assuming system supports %d pids.", filename, pid_max);
            return pid_max;
        }
    
        pid_max = (pid_t) max;
        return pid_max;
    }
    
    int main() {
        
        get_system_pid_max();
    
        printf("pid_max = %d", pid_max);
    
        return 0;
    }
    
    
    static inline int read_single_number_file(const char *filename, unsigned long long *result) {
        
        char buffer[30 + 1];
    
        int ret = read_file(filename, buffer, 30);
        if(unlikely(ret)) {
        
            *result = 0;
            return ret;
        }
    
        buffer[30] = '\0';
        *result = str2ull(buffer);
        return 0;
    }
    
    static inline int read_file(const char *filename, char *buffer, size_t size) {
        
        if(unlikely(!size)) return 3;
    
        int fd = open(filename, O_RDONLY, 0666);
        if(unlikely(fd == -1)) {
        
            buffer[0] = '\0';
            return 1;
        }
    
        ssize_t r = read(fd, buffer, size);
        if(unlikely(r == -1)) {
        
            buffer[0] = '\0';
            close(fd);
            return 2;
        }
        buffer[r] = '\0';
    
        close(fd);
        return 0;
    }
    static inline unsigned long long str2ull(const char *s) {
        
        unsigned long long n = 0;
        char c;
        for(c = *s; c >= '0' && c <= '9' ; c = *(++s)) {
        
            n *= 10;
            n += c - '0';
        }
        return n;
    }

![在这里插入图片描述][20210104224940496.png]

# 测试系统最多能够创建多少线程数 #

#include <zconf.h>
    #include <pthread.h>
    #include <stdio.h>
    #include <string.h>
    #include <errno.h>
    
    void *foo(void *arg)
    {
        
        return((void *)0);
    }
    int main()
    {
        
        int i = 0;
        pthread_t thread;
    
        while (1) {
        
            if (pthread_create(&thread, NULL, foo, NULL) != 0){
        
                printf("%s", strerror(errno));
                return 0;
            }
    
            i ++;
            printf("i = %d\n", i);
        }
    }

![在这里插入图片描述][20210105105715446.png]

[20210104224940496.png]: /images/20221120/637588e20a634595849908d70dd9ce4c.png
[20210105105715446.png]: /images/20221120/14d9e8a4018740169c53d8499b0d74c0.png