undefined reference to `pthread_create'

Linux中編譯pthread需要加上參數，參考man pthreads

Compiling on Linux
On Linux, programs that use the Pthreads API should be compiled using cc
-pthread.

Simple Shell in Unix

用C練習了一個簡單的shell，在這做一下重點筆記。

#include                                      
...
                                                                    
#define MAXLINE 80 
...                                  

void handle_SIGINT();
...

int hindex;
...            

void handle_SIGINT(){
        int i = hindex - 1;
        char tmp[MAXLINE]; 
        write(STDOUT_FILENO, "\nHistroy:\n", 10);
        for(;i > (hindex - 10) && i >= 0;i--){   
                ...
        }                                              

        signal(SIGINT, handle_SIGINT);
        write(STDOUT_FILENO, "\n COMMAND->", 11);
}                                                

void processBuffer(char inputBuffer[], char* args[], int length, int* background){
        /* 處理inputBuffer，把他變成一個一個arg儲存在args中 */
}                                                                                            

void readHistory(char* args[], char fletter, int* background){
        int i;                                                
        for(i = hindex - 1; i >= (hindex-10); i--)            
                if(*history[i] == fletter) break;             
        strcpy(history[hindex - 1], history[i]);              
        processBuffer(history[i], args, strlen(history[i]), background);
}                                                                       


void setup(char inputBuffer[], char* args[], int* background){
        /* 讀入user input並且呼叫processBuffer負責處理，順便紀錄在history中 */
}

int main(void){
        char inputBuffer[MAXLINE];
        int background; /* indicate if the program run in background when '&' at the end */
        char* args[MAXLINE/2 + 1];

        hindex = 0; /* initilize the history index which point to the next history storage */


        while(1){
                background = 0;
                printf(" COMMAND->");
                fflush(stdout);
                signal(SIGINT, handle_SIGINT); /* set up, when program received the control + c
                                                  it will invoke the handle_SIGINT function */
                setup(inputBuffer, args, &background);
                if(!fork()){
                        execvp(args[0], args);
                }else{
                        if(!background)
                                wait();
                }
        }
}

signal(SIGINT, handle_SIGINT);

是收到signal時，會呼叫哪個function來處理。

原始檔案連結:Link

Shared Memory Segment's Infomation

每個Segment的相關資料，都可以經由shmctl(segment_id, IPC_STAT, &shmbuffer)來取得

而shmbuffer是struct shmid_ds (在/usr/include/sys/shm.h中)，

裏面有些欄位來說明一下：

int shm_segsz: size of the shared memory

short shm_nattch: number of attaches to the segment

struct ipc_perm shm_perm:permission structure

而ipc_perm在/usr/include/sys/ipc.h中，裏面有些欄位是

unsigned short uid: identifier of the user of the segment

unsigned short mode : permission modes

key_t key(on linux is __key) : user-specified key identifier

下面是個簡單的實作範例：

#include 
#include 
#include 
#include 

int main(){
        int segment_id;
        struct shmid_ds shmbuffer;

        segment_id = shmget(IPC_PRIVATE, 4096, S_IRUSR | S_IWUSR);
        shmctl(segment_id, IPC_STAT, &shmbuffer);
        printf("Seg ID\tKey\tMode\tOwner\tSize\tAttaches\n");
        printf("%d\t%d\t%o\t%d\t%d\t%d\n", segment_id, shmbuffer.shm_perm.__key,
                shmbuffer.shm_perm.mode, shmbuffer.shm_perm.uid, shmbuffer.shm_segsz,
                shmbuffer.shm_nattch);
        shmctl(segment_id, IPC_RMID, NULL);
        return 0;
}

不過unix中有提供一個工具是ipcs就是類似這的output了，只是這裡寫的是極陽春版....

Linux IPC (Shared memory)

一個簡單的程式，利用Child算好fabonacci數列後，還回給parent print。

在這之間是利用shared memory來傳遞資料的！

#include                                             
#include                                            
#include                                           
#include                                          
#include "../lib/string.c"                                    
#define MAX_SEQUENCE 10                                       
#define DEBUG 1                                               

typedef struct {
        long seq[MAX_SEQUENCE];
        int seq_size;          
} shared_data;                 

int main(int argc, char* argv[]){
        int segment_id, pid;     
        char *shared_memory;     
        shared_data fib_seq;     
        const int size = 4096;   

        if(argc != 2){
                 fprintf(stderr, "Usage: %s seq_size\n", argv[0]);
                 return -1;                                       
        }                                                         
        fib_seq.seq_size =  atoi(argv[1]);                        
        if(fib_seq.seq_size > MAX_SEQUENCE){                      
                 fprintf(stderr, "seq_size overflow.\n");         
                 return -1;                                       
        }                                                         

        segment_id = shmget(IPC_PRIVATE, size, S_IRUSR | S_IWUSR);

        if(!(pid = fork())){
                shared_memory = (char *) shmat(segment_id, NULL, 0);

                fib_seq.seq[0] = 0;
                fib_seq.seq[1] = 1;

                int i;
                if(DEBUG) fprintf(stderr, "Counting Fabonacii...\n");
                for(i = 2; i < fib_seq.seq_size; i++)
                        fib_seq.seq[i] = fib_seq.seq[i-2] + fib_seq.seq[i-1];

                if(DEBUG) fprintf(stderr, "Converting each int to string...\n");
                char* fib_str[fib_seq.seq_size];
                for(i = 0; i < fib_seq.seq_size; i++)
                        fib_str[i] = itoa(fib_seq.seq[i]);

                if(DEBUG) fprintf(stderr, "Join the seq to string...\n");
                char* return_str = join_strings(fib_str, fib_seq.seq_size, ',');

                sprintf(shared_memory, "%s\n", return_str);
                shmdt(shared_memory);
                return 0;
        }else{
                wait(NULL);
                if(DEBUG) fprintf(stderr, "Back to parent...\n");
                shared_memory = (char *) shmat(segment_id, NULL, 0);
                printf("%s", shared_memory);
                shmdt(shared_memory);
                shmctl(segment_id, IPC_RMID, NULL);

                return 0;
        }
}

在DEBUG訊息中都有寫上註解了。
簡單說明一下sharedmem的一些system call
segment_id = sgmget(....) //分配shared memory的空間
shared_memory = (char *) shmat(....) //使程式取得該shared mem的pointer
shmdt(shared_memory) //中斷與shared mem的連結
shmctl(...) //清除shared mem region