pthread

了解thread

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item	note
20161206	第一版

What is a Thread

thread

即共用process的data,text,headp
獨立的stack及register等
使用pthread library來實現

出處：An introduction to UNIX processes

process包含下例訊息
- Process ID, process group ID, user ID, and group ID (process是依使用者有不同的pid)
- Environment
- Program instructions (text:存放程式碼)
- Registers
- Stack
- Heap
- File descriptors
- Signal actions
- Shared libraries
- Inter-process communication tools (such as message queues, pipes, semaphores, or shared memory).
Threads use and exist within these process resources
This independent flow of control is accomplished because a thread maintains its own:
- Stack pointer
- Registers
- Scheduling properties (such as policy or priority)
- Set of pending and blocked signals
- Thread specific data. (ex.Thread ID)

三種記憶體區間: global、stack、heap
global: 全域變數、靜態變數(static)
stack: 區域變數、函式的參數與函式的位址等,由系統管理，必須在編譯時期為已知
heap: 這裡的記憶體由使用者負責進行回收，配置則是由malloc或是new來負責

example

pthread_create函数的详细讲解
pthred_create取得的ntid(即thread id)
也可以使用pthread_self
main及父process，與建立的thread為同1個pid

main.c

$ cat main.c 
#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>

pthread_t ntid;

void printids(const char *s){
    pid_t       pid;
    pthread_t   tid;
    pid = getpid();
    tid = pthread_self();

    printf("%s pid %u tid %u (0x%x)\n",s,(unsigned int)pid, (unsigned int)tid, (unsigned int)tid);
}

void *thr_fn(void *arg){
    printids("new thread:");
    return ((void *)0);
}

int main(void){
    int     err;
    err = pthread_create(&ntid,NULL,thr_fn,NULL);

    if( err != 0){
        printf("can't create thread; %s\n",strerror(err));
    }else{
        printf("ntid %u (0x%x)\n",(unsigned int)ntid,(unsigned int)ntid);
        printids("main thread;");
        sleep(1);
        exit(0);
    }
}

a.out

$ ./a.out 
ntid 1990027008 (0x769d6700)
main thread; pid 11778 tid 1998260032 (0x771b0740)
new thread: pid 11778 tid 1990027008 (0x769d6700)

其它說明

Creating and Terminating Threads

pthread_create (thread,attr,start_routine,arg)

pthread_exit (status)

pthread_cancel (thread)

pthread_attr_init (attr)

pthread_attr_destroy (attr)

pthread_create - create a new thread

1	int pthread_create(pthread_t thread, const pthread_attr_t attr,void (start_routine) (void ), void arg);

父process使用pthread_join來等待thread的結束
The new thread terminates in one of the following ways
- pthread_exit
  terminate calling thread
  1
  void pthread_exit(void *retval);
- pthread_cancel
  send a cancellation request to a thread
  phtread_join收到的exit stats為PTHREAD_CANCELED
  1
  int pthread_cancel(pthread_t thread);
- pthread_self
  obtain ID of the calling thread

pthread_join和pthread_detach的用法
一般使用pthread_join來等待結束並且將释放所有资源
也可以使用pthread_detach
pthread_detach
pthread_detach(thread_id)（非阻塞，可立即返回）
这将该子线程的状态设置为detached,则该线程运行结束后会自动释放所有资源。

Process

unixprocess說明如下

What is Process
UNIX中Pocess代表一個具有獨立記憶空間、可單獨運作的”工作空間”(Program),每一件系統或User的工作均由各種不同的process完成之
Why Process
NIX中，很多resource的管理，必須藉由process的控制來完成UNIX每一個程序都有一個唯一的識別代號，我們稱之為程序代號(process id or pid)
How Process Works
每一process在必要情況之下由其Parent Process產生，完成工作之後會自動釋放所有佔用的系統資源，結束並系開系統。
Process的產生
fork-and-exec是UNIX中所有process運作的模式
Process的結束
Process結束退出系統前，會放棄所有佔用之系統resource，並分別送出訊號通知parent process及child process。
如果因某些原因，parent process在其結束前即已不存在，此 process即成為所謂的Zombie process(or defunct process)，無法正常結束。

top

Mem: 30584K used, 215460K free, 0K shrd, 0K buff, 5944K cached
CPU:  0.0% usr  0.0% sys  0.0% nic  100% idle  0.0% io  0.0% irq  0.0% sirq
Load average: 7.76 2.40 0.83 1/59 912
  PID  PPID USER     STAT   VSZ %VSZ CPU %CPU COMMAND
  904     1 root     S     1440  0.5   1  0.0 -sh
  912   904 root     R     1432  0.5   1  0.0 top
    1     0 root     S     1428  0.5   0  0.0 init
  653     1 root     S     1428  0.5   1  0.0 /usr/sbin/telnetd
    4     2 root     SW       0  0.0   0  0.0 [kworker/0:0]
   12     2 root     SW       0  0.0   1  0.0 [kworker/1:0]
   10     2 root     SW       0  0.0   1  0.0 [migration/1]
  342     2 root     SW       0  0.0   1  0.0 [kworker/1:1]
    3     2 root     SW       0  0.0   0  0.0 [ksoftirqd/0]
    7     2 root     SW       0  0.0   0  0.0 [migration/0]
    2     0 root     SW       0  0.0   3  0.0 [kthreadd]
   11     2 root     SW       0  0.0   1  0.0 [ksoftirqd/1]
    9     2 root     SW       0  0.0   1  0.0 [rcu_sched]
   14     2 root     SW       0  0.0   2  0.0 [migration/2]
   15     2 root     SW       0  0.0   2  0.0 [ksoftirqd/2]
   16     2 root     SW       0  0.0   2  0.0 [kworker/2:0]
   13     2 root     SW<      0  0.0   1  0.0 [kworker/1:0H]
    5     2 root     SW<      0  0.0   0  0.0 [kworker/0:0H]
    6     2 root     SW       0  0.0   0  0.0 [kworker/u8:0]
   20     2 root     SW       0  0.0   3  0.0 [kworker/3:0]

USER:
Username of the process owner
PID:
Process ID
PPID:
That’s the parent’s PID.
Every (well, almost) process has a parent process, the process that was responsible for its creation.
STAT: Process state
R Running
S Sleeping
I Idle
Z Zombie
An introduction to UNIX processes ,Summarizing
- A process is an instance of a running program;
- Processes have some properties related to it (pid, ppid, tty, etc.);
- Processes are created in a two step process: exec and fork;
- Processes always exit with an exit code;
- A process is a zombie if it is already dead but its parent still didn’t read its exit code with wait;
- A process is an orphan if it is still alive but its parent isn’t. The init process becomes the new parent;
- A daemon is a process that runs in the background, and is not attached to a controlling terminal;
- Signals are messages sent from one process to another.

pthread

更新記錄

目錄

What is a Thread

example

其它說明

Process

參考