Ch4 Linux System Programming – Process & IPC

Jianjian SONGSoftware Institute, Nanjing UniversityOct, 2004

Content

1. Process & process environment2. Process Control

Process identifier, fork, exec…3. Process relationship4. Signal5. Inter-process communication (IPC)

Pipe, FIFO semaphore, shared memory, message

queue6. Daemon7. Thread

1. Process & Process Environment

What is a process? Program and process Process: an address space with one or

more threads executing within that address space, and the required system resources for those threads. (SUSv3)

The startup of a process

System call “fork” Process resources

struct task_struct System space stack …

System call “exec” The entry of C programs

System stack

The entry of C programs

crt0.o cc/ld

main function function prototype ：

int main(int argc, char *argv[]);

The termination of a process

Five ways of terminating a process Normal termination

Return from “main” function Call “exit” function Call “_exit” function

Abnormal termination Call “abort” function Terminated by a signal

exit & _exit functions

Function prototype:#include <stdlib.h>void exit(int status);#include <unistd.h>void _exit(int status);

Exit status Difference

_exit is corresponding to a system call, while “exit” is a library function.

_exit terminate a process immediately.

Exit handler

atexit function Register a function to be called at normal

program termination. Prototype:

#include <stdlib.h>int atexit(void (*function)(void));

on_exit function Example

The memory map of a C program

Text segment (code segment) Data segment

Initialized data Uninitialized data Heap

Stack

Command line arguments

main functionint main(int argc, char *argv[]);

Example: The implementation of echo(1)

Command line option Standard usage getopt function

getopt function Prototype:

int getopt(int argc, char *const argv[], const char *optstring);extern char *optarg;extern int optind, opterr, optopt;

Question ： getopt(argc, argv, “if:lr”); Program example (P104, in BLP)

Environment variables

Environment table Environment pointer

extern char **environ;

putenv & getenv functions Get, set or unset an environment varia

ble#include <stdlib.h>char *getenv(const char *name);int putenv(char *string);int setenv(const char *name, const char *value, in

t overwirte);void unsetenv(const char *name);

Shared object

Shared object Dynamic link Advantages and disadvantages Example

How to create a static and shared library? How to use (link) a static or shared

library?

Memory allocation

Allocate and free dynamic memory.#include <stdlib.h>void *malloc(size_t size);void *calloc(size_t nmemb, size_t size);void free(void *ptr);void realloc(void *ptr, size_t size);

2. Process control

Process identifier System call “fork” The simple synchronization

between parent and child process The “exec” function family Example:

The implementation of a simple shell

Process identifier

fork

fork: create a child process#include <sys/types.h>#include <unistd.h>pid_t fork(void);

returned value: pid of child (in the current (parent) process), 0 (in child process), -1 (failure)

A simple example

#include <stdio.h>#include <sys/types.h>#include <unistd.h>

/* fork 系统调用的第一个例子（不含错误检查） */void main(){

printf(“Hello, world!\n”);fork();printf(“bye\n”);

}

The usage of “fork” Code example

if ( (pid=fork()) < 0) { /* error handling */} else if (pid == 0) { /* child */} else { /* parent */};

Program example Program8-1 in APUE

File sharing 所有由父进程打开的描述符都被复制到子进程

中。父、子进程每个相同的打开描述符共享一个文件表项

vfork & clone functions vfork

#include <sys/types.h>#include <unistd.h>pid_t vfork(void);

clone#include <sched.h>int clone(int (*fn)(void *), void *child_stack,

int flag, void *arg);

The simple synchronization between parent and child process

The relationship between parent and child process

wait and waitpid functions

The relationship between parent and child process

The parent terminates before the child Orphan process

The child terminates before the parent SIGCHLD signal Handled by wait/waitpid in parent Not handled by wait/wait in parent -> zombi

e

wait & waitpid functions Wait for process termination Prototype

#include <sys/types.h>#include <sys/wait.h>pid_t wait(int *status);pid_t waitpid(pid_t pid, int *status, int options);

Example

Race condition

int main(void){ pid_t pid;

if ( (pid = fork()) < 0) err_sys("fork error"); else if (pid == 0) { charatatime("output cccccccccccc from child\n"); } else { charatatime("output pppppppppp from parent\n"); } exit(0);}

An improvementint main(void){ pid_t pid; TELL_WAIT(); if ( (pid = fork()) < 0) err_sys("fork error"); else if (pid == 0) { WAIT_PARENT(); /* parent goes first */ charatatime("output cccccccccccc from child\n"); } else { charatatime("output pppppppppp from parent\n"); TELL_CHILD(pid); } exit(0);}

The “exec” family of functions

Replace the current process image with a new process image.

执行新程序的进程保持原进程的一系列特征： pid, ppid, uid, gid, working directory, root direc

tory … euid/egid? 打开文件描述符 ?

Functions prototypes

#include <unistd.h>extern char **environ;int execl(const char *path, const char *arg, ...);int execlp(const char *file, const char *arg, ...);int execle(const char *path, const char *arg, ..., char *

const envp[]);int execv(const char *path, char * const argv[]);int execvp(const char *file, char * const argv[]);

#include <unistd.h>int execve(const char *filename, char * const argv[], c

har * const envp[]);

exec and opened file descriptor

close-on-exec bit of a file descriptor Set by “fcntl” function

fcntl(fd, F_SETFD, 0); /* 系统默认 , 打开文件描述符在 exec 时不关闭 */

fcntl(fd, F_SETFD, 1); /* 打开文件描述符在 exec 时关闭 */

Using fork and exec together

Two ways of using fork The parent process duplicates itself, and then tw

o different pieces of codes are executed in parent process and child process.

A process want to execute another program. Example:

The implementation of “system” function int system(const char*cmdstring);

Example: a simple shellprintf("%% "); /* print prompt */while (fgets(buf, MAXLINE, stdin) != NULL) { buf[strlen(buf) - 1] = 0; /* replace newline with null */ if ( (pid = fork()) < 0 ) err_sys(“fork error”); else if ( pid == 0 ) { /* child */ execlp(buf, buf, (char *) 0); fprintf(stderr, "couldn't execute: %s", buf); exit(127); } if ( (pid = waitpid(pid, &status, 0)) < 0 ) /* parent */ err_sys(“waitpid error”); printf("%% ");}

3. Process relationship

父进程和子进程 进程树

ps, pstree 命令

Startup & login (1)

Login on serial terminal

Startup & login (2)

Network login

Process group & session

Process group The set of one or more process(es). getpgrp/setpgid functions

Session The set of one or more process group(s). setsid function

Controlling terminal Why are they introduced?

Job control

Process group & session (cont’d)

Process group & session (cont’d)

4. Signal

The concept of signals The “signal” function Send a signal

kill, raise The “alarm” and “pause” functions Reliable signal mechanism

The concept of signals

Signal Software interrupt Mechanism for handling asynchronous events Having a name (beginning with SIG) Defined as a positive integer (in <signal.h>)

How to produce a signal 按终端键，硬件异常， kill(2) 函数， kill(1) 命令，

软件条件， ...

Signals in Linux/UNIX

名称 说明SIGABRT 进程异常终止（调用 abort 函数产生此信号）SIGALRM 超时（ alarm ）SIGFPE 算术运算异常（除以 0 ，浮点溢出等）SIGHUP 连接断开SIGILL 非法硬件指令SIGINT 终端终端符 (Clt-C)SIGKILL 终止（不能被捕捉或忽略）SIGPIPE 向没有读进程的管道写数据SIGQUIT 终端退出符 (Clt-\)SIGTERM 终止（由 kill 命令发出的系统默认终止信号）SIGUSR1 用户定义信号SIGUSR2 用户定义信号

Signals in Linux/UNIX (cont’d)

名称 说明SIGSEGV 无效存储访问（段违例）SIGCHLD 子进程停止或退出SIGCONT 使暂停进程继续SIGSTOP 停止（不能被捕捉或忽略）SIGTSTP 终端挂起符 (Clt-Z)SIGTTIN 后台进程请求从控制终端读SIGTTOUT 后台进程请求向控制终端写

Signal handling

忽略信号 不能忽略的信号：

SIGKILL, SIGSTOP 一些硬件异常信号

执行系统默认动作 捕捉信号

The “signal” function

Installs a new signal handler for the signal with number signum.

#include <signal.h>typedef void (*sighandler_t)(int);sighandler_t signal(int signum, sighandler_t handler);

(Returned Value: the previous handler if success, SIG_ERR if error)

The “handler” parameter a user specified function, or SIG_DEF, or SIG_IGN

The ”signal” function (cont’d) Program example

static void sig_usr(int);int main(void){ if (signal(SIGUSR1, sig_usr) == SIG_ERR) err_sys("can't catch SIGUSR1"); if (signal(SIGUSR2, sig_usr) == SIG_ERR) err_sys("can't catch SIGUSR2");

for ( ; ; ) pause();}

Send a signal

kill(2): send signal to a process#include <sys/types.h>#include <signal.h>int kill(pid_t pid, int sig);

(Returned Value: 0 if success, -1 if failure) raise(3): send a signal to the current process

#include <signal.h>int raise(int sig);

(Returned Value: 0 if success, -1 if failure)

alarm & pause functions

alarm: set an alarm clock for delivery of a signal#include <unistd.h>unsigned int alarm(unsigned int seconds);

(Returned value: 0, or the number of seconds remaining of previous alarm)

pause: wait for a signal#include <unistd.h>int pause(void);

(Returned value: -1, errno is set to be EINTR)

alarm & pause functions (cont’d)

Program example The implementation of the “sleep” fun

ctionunsigned int sleep1(unsigned int nsecs){ if ( signal(SIGALRM, sig_alrm) == SIG_ERR) return(nsecs); alarm(nsecs); /* start the timer */ pause(); /*next caught signal wakes us up*/ return(alarm(0) ); /*turn off timer, return unslept time */}

Possible problems

Problems related to time Race condition Interrupted system calls Reentrancy

Reliable signal mechanism

Weakness of the signal function Signal block

signal mask Signal set

sigset_t data type Signal handling functions using signal set

sigprocmask, sigaction, sigpending, sigsuspend

signal set operations

#include <signal.h>

int sigemptyset(sigset_t *set);int sigfillset(sigset_t *set);int sigaddset(sigset_t *set, int signum);int sigdelset(sigset_t *set, int signum); (Return value: 0 if success, -1 if error)

int sigismember(const sigset_t *set, int signum); (Return value: 1 if true, 0 if false)

sigprocmask function 检测或更改 ( 或两者 ) 进程的信号掩码

#include <signal.h>sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

(Return Value: 0 is success, -1 if failure)

参数“ how” 决定对信号掩码的操作 SIG_BLOCK: 将 set 中的信号添加到信号掩码 ( 并集 ) SIG_UNBLOCK: 从信号掩码中去掉 set 中的信号 ( 差集 ) SIG_SETMASK: 把信号掩码设置为 set 中的信号

例外 : SIGKILL, SIGSTOP

sigpending function 返回当前未决的信号集

#include <signal.h>sigpending(sigset_t *set);

(Returned Value: 0 is success, -1 if failure)

Example: critical.c (Prog10-11 in APUE)

sigaction function 检查或修改 ( 或两者 )与指定信号关联的处理动作

#include <signal.h>sigaction(int signum, const struct sigaction *act, struct sigac

tion *oldact);(Returned Value: 0 is success, -1 if f

ailure) struct sigaction至少包含以下成员 :

handler_t sa_handler; /* addr of signal handler, or SIG_IGN, or SIG_DEL */

sigset_t sa_mask;/* additional signals to block */int sa_flags; /* signal options */

sigsuspend function 用 sigmask临时替换信号掩码，在捕捉一个信号或发

生终止该进程的信号前，进程挂起。#include <signal.h>sigsuspend(const sigset *sigmask);

(Returned value: -1, errno is set to be EINTR) sigsuspend 和 pause

signal function review 用 sigaction实现 signal 函数

Sigfunc * signal(int signo, handler_t func) {struct sigaction act, oact;act.sa_handler = func;sigemptyset(&act.sa_mask);act.sa_flags = 0;if (signo == SIGALRM) {

#ifdef SA_INTERRUPTact.sa_flags |= SA_INTERRUPT; /* SunOS */

#endif} else {

#ifdef SA_RESTARTact.sa_flags |= SA_RESTART; /* SVR4, 44BSD */

#endif}if (sigaction(signo, &act, &oact) < 0)

return(SIG_ERR);return(oact.sa_handler);

}

Example: solution of race conditionint main(void){ pid_t pid; TELL_WAIT(); if ( (pid = fork()) < 0) err_sys("fork error"); else if (pid == 0) { WAIT_PARENT(); /* parent goes first */ charatatime("output cccccccccccc from child\n"); } else { charatatime("output pppppppppp from parent\n"); TELL_CHILD(pid); } exit(0);}

static sigset_t newmask, oldmask, zeromask;static void sig_usr(int signo) {/* one handler for SIGUSR1, SIGUSR2 */

sigflag = 1; return;}void TELL_WAIT() {

if (signal(SIGUSR1, sig_usr) == SIG_ERR)err_sys("signal(SIGINT) error");

if (signal(SIGUSR2, sig_usr) == SIG_ERR)err_sys("signal(SIGQUIT) error");

sigemptyset(&zeromask);sigemptyset(&newmask);sigaddset(&newmask, SIGUSR1);sigaddset(&newmask, SIGUSR2);

/* block SIGUSR1 and SIGUSR2, and save current signal mask */if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)

err_sys("SIG_BLOCK error");}

void WAIT_PARENT(void) {while (sigflag == 0)

sigsuspend(&zeromask); /* and wait for parent */

sigflag = 0;/* reset signal mask to original value */if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)

err_sys("SIG_SETMASK error");}

void TELL_CHILD(pid_t pid) {kill(pid, SIGUSR1); /* tell child we're done */

}

5. Inter-process communication

IPC: Inter-Process Communication IPC mechanisms

shared file signal pipe, FIFO (named pipe), message

queue, semaphore, shared memory socket

IPC illustrations

Simple Client-Server or IPC model

The concept of pipe

Pipe Pipe mechanism in a shell

e.g. cmd1 | cmd2 Pipe is half-duplex 管道只能在共同祖先的进程间使用 管道也是文件 命名管道 (FIFO)

The pipe function

The pipe function: create a pipe#include <unistd.h>int pipe(int filedes[2]);

(Returned value: 0 if success, -1 if failure) A pipe: First In, First Out

filedes[0]:read, filedes[1]: write

A pipe in a single process

A pipe between the parent & child

The coordinationof pipe read & write

写管道时，常数 PIPE_BUF规定了内核中管道缓存器的大小

管道的一端关闭时， 写端关闭，读该管道在所有数据都被读取后，

read返回 0 ，表示达到了文件结束 读端关闭，写该管道产生信号 SIGPIPE

Examples

pipe1.c

管道用于标准输入和标准输出 管道： shell 中的形式

cmd1 | cmd2 重定向 cmd > file

实现代码 执行 cmd1前

if (fd[1] != STDOUT_FILENO) {if (dup2(fd[1], STDOUT_FILENO) != STDOUT_FILENO)

err_sys(“dup2 error to stdout);}

执行 cmd2前if (fd[0] != STDIN_FILENO) {

if (dup2(fd[0], STDIN_FILENO) != STDIN_FILENO) err_sys(“dup2 error to stdin);}

Examples

pipe2.c

pipe Application(1):solution of race conditionint main(void){ pid_t pid; TELL_WAIT(); if ( (pid = fork()) < 0) err_sys("fork error"); else if (pid == 0) { WAIT_PARENT(); /* parent goes first */ charatatime("output cccccccccccc from child\n"); } else { charatatime("output pppppppppp from parent\n"); TELL_CHILD(pid); } exit(0);}

static int pfd[2];void TELL_WAIT() {

if (pipe(pfd) < 0)err_sys("pipe error");

}void WAIT_PARENT(void) {

char c;if (read(pfd[0], &c, 1) != 1)

err_sys("read error");if (c != 'p')

err_quit("WAIT_PARENT: incorrect data");}void TELL_CHILD(pid_t pid) {

if (write(pfd[1], "p", 1) != 1)err_sys("write error");

}

pipe Application(2): shell

shpipe.c

popen & pclose functions popen, pclose: process I/O

#include <stdio.h>FILE *popen(const char *command, const char *type);int pclose(FILE *stream);

按页输出 在程序中获得另一个程序的输出

Applications of popen & pclose

Home work: popen 的实现 用 pipe, fork实现 popen

FIFO: named pipe

管道和命名管道 相同点 不同点

文件系统中 同步：一个重要的考虑

mkfifo(1), mkfifo(3), mknod(1), mknod(2)

创建 FIFO mkfifo: make a FIFO special file (a named pi

pe)#include <sys/types.h>#include <sys/stat.h>int mkfifo(const char *pathname, mode_t mode);

(Returned value: 0 if success, -1 if failure) Examples

fifo1.c (Ch12 in BLP) list a fifo (ls –lF)

用 open 打开一个 FIFO Review: “open” system call

int open(const char *pathname, int flags); “flags” parameter

必须指定的互斥模式 :O_RDONLY, O_WRONLY, O_RDWR

O_NONBLOCK consideration ：

读端 / 写端 同步

FIFO 的同步和读写 打开 FIFO 时的同步

一般情况下（没有说明 O_NONBLOCK ），只读打开要阻塞到某个其它进程为写打开此 FIFO；类似的，为写打开一个 FIFO要阻塞到某个其它进程为读而打开它。

如果指定了 O_NONBLOCK ，则只读打开立即返回；只写打开也立即返回，但如果没有进程已经为读而打开此 FIFO ，那么 open 将出错返回 -1 ， errno置为 ENXIO 。

读写 FIFO 时的同步 same as pipe

同步示例 shell 中使用 fifo 的例子

cat < my_fifoecho “a string to fifo” > my_fifo

fifo2.c (Ch12 in BLP)

FIFO 的应用 (1) 用 FIFO 复制输出流

例

FIFO 的应用 (2) C/S应用程序

例： client.c, server.c

System V IPC

IPC objects 信号量 (semaphore set) 消息队列 (message queue) 共享内存 (shared memory)

shell 命令 ipcs, ipcrm

System V IPC 的共同特征 标识符与关键字

引用 IPC 对象：标识符 创建 IPC 对象时指定关键字 (key_t key;)

key 的选择；预定义常数 IPC_PRIVATE； ftok 函数 内核将关键字转换成标识符

许可权结构 和文件类比 struct ipc_perm

SV IPC System Calls Overview

功能 消息队列 信号量 共享内存分配一个 IPC 对象，获得对 IPC 的访问

msgget semget shmget

IPC 操作 : 发送 / 接收消息，信号量操作，连接 /释放共享内存

msgsnd/msgrcv

semop shmat/shmdt

IPC 控制：获得 /修改状态信息，取消 IPC

msgctl semctl shmctl

Semaphore

并发程序设计 互斥和同步 PV 操作 ( 原语 )

PV 操作和信号量procedure p(var s:samephore){ s.value=s.value-1; if (s.value<0) asleep(s.queue); }

procedure v(var s:samephore){ s.value=s.value+1; if (s.value<=0) wakeup(s.queue); }

Linux/UNIX 的信号量机制 semaphore set struct semid_ds

struct ipc_perm sem_perm; struct sem *sem_base; /* ptr to first sem in set */ time_t sem_otime; /* last operation time */ time_t sem_ctime; /* last change time */ ushort sem_nsems; /* count of sems in set */

semaphore set system calls

#include <sys/types.h>#include <sys/ipc.h>#include <sys/sem.h>

int semget(key_t key, int nsems, int semflg);int semop(int semid, struct sembuf *sops, unsigned nsops);int semctl(int semid, int semnum, int cmd, ...);

semget: get a semaphore set identifier prototype

int semget(key_t key, int nsems, int semflg); “key” parameter

预定义常数 IPC_PRIVATE； 约定的关键字 ftok 函数

“semflg” parameter 设置访问权限 (低 9位 ) IPC_CREAT, IPC_EXCL 按位或

examples sem1.c

semop: semaphore operations prototype

int semop(int semid, struct sembuf *sops, unsigned nsops); “sops” parameter

struct sembuf { unsigned short int sem_num; /* semaphore number */ short int sem_op; /* semaphore operation */ short int sem_flg; /* operation flag */}

examples: PV 操作的实现

semctl: semaphore control operations prototype

int semctl(int semid, int semnum, int cmd, ...); the 4th argument

union semun{ int val; struct semid_ds *buf; unsigned short *array;} arg;

“cmd” parameter

semctl: semaphore control operations (cont’d) “cmd” parameter

IPC_STAT: 对指定的信号量标识返回 arg.semid_ds结构中的当前值

IPC_SET: 在进程有足够权限的前提下，把信号量集合的当前关联值置为 arg.semid_ds结构给出的值

IPC_RMID: 删除信号量集合 SETVAL: 设置信号量集合中由 semnum 指定的单个

信号量的值 ( 设为 arg.val) examples

set_semvalue(初始化 ), del_semvalue(结束 )

Examples

一个完整的实例 sem1.c( 进程互斥 )

Home work:

用程序模拟实现生产者 /消费者问题 进程同步

Message queue

消息队列 消息队列是消息的链表，存放在内核中并由消息队列标识符标识。

First in, first out message type: 优先级 块数据

struct msqid_ds

message queue system calls

#include <sys/types.h>#include <sys/ipc.h>#include <sys/msg.h>

int msgget(key_t key, int size, int flag);int msgsnd(int msqid, const void *ptr, size_t nbytes, int flag);int msgrcv(int msqid, void *ptr, size_t nbytes, long type, int flag);int msgctl(int msqid, int cmd, struct shmid_ds *buf);

msgctl: message control operations prototype

int msgctl(int msqid, int cmd, struct shmid_ds *buf);

“cmd” parameter IPC_STAT: 把 msqid_ds结构中的数据置为消息队

列的当前关联值 IPC_SET: 在进程有足够权限的前提下，把消息队

列的当前关联值置为msqid_ds结构给出的值 IPC_RMID: 删除消息队列

Example

A C/S application One server, several clients: only one

queue is required. Compared with FIFO implementation

Shared memory

共享内存 共享内存是内核为进程创建的一个特殊内存

段，它可连接 (attach) 到自己的地址空间，也可以连接到其它进程的地址空间

最快的进程间通信方式 不提供任何同步功能

shared memory system calls

#include <sys/types.h>#include <sys/ipc.h>#include <sys/shm.h>

int semget(key_t key, int size, int flag);void *shmat(int shmid, void *addr, int flag);int shmdt(void *addr);int shmctl(int shmid, int cmd, struct shmid_ds *buf);

mmap/munmap system calls mmap/munmap: map or unmap files

or devices into memory

6. Daemon process

什么是 daemon 进程 daemon 进程的实现方法

编程规则 出错记录

What is a daemon?

What is a daemon? (cont’d)

daemon 精灵进程或守护进程 后台执行 , 没有控制终端或登录 Shell 的进

程 why daemon?

Concepts related to job control

Process group & session Controlling terminal jobs, fg, bg comands SIGINT, SIGQUIT, SIGTSTP, SIGHUP signal

s A solution the problem

nohup command & >> logfile

daemon 进程的实现 (1) 编程规则

首先调用 fork ，然后使父进程 exit 调用 setsid创建一个新的会话期 将当前工作目录更改为特定目录 进程的 umask 设为 0 关闭不需要的文件描述符

Exampleint daemon_init(void) {

pid_t pid;

if ( (pid = fork()) < 0)return(-1);

else if (pid != 0)exit(0); /* parent goes bye-bye */

/* child continues */setsid(); /* become session leader */chdir("/"); /* change working directory */umask(0); /* clear our file mode creation mask */

return(0);}

daemon 进程的实现 (2) 出错记录

7. Threads

What is a thread Basic pthread functions Thread synchronization Thread attributes Thread cancellation

What is a thread?

Thread: A single flow of control within a process.

(susv3) Process and thread

New process: when a process executes a fork call, a new copy of the process is created with its own variables and its own PID.

New thread: When we create a new thread in a process, the new thread of execution gets its own stack (and hence local variables) but shares global variables, file descriptors, signal handlers, and its current directory state with the process that created it.

Process and thread

POSIX thread

POSIX1003.1c pthread library

/usr/lib/libpthread.so, /usr/lib/libpthread.a pthread.h header file

/usr/include/pthread.h Compiler options

gcc thread.c –o thread -lpthread

Basic thread functions(1)

Create a new thread#include <pthread.h>int pthread_create(pthread_t *thread, pthread_attr_t *attr,

void *(*start_routine)(void *), void *arg); Terminate the calling thread

void pthread_exit(void *retval);

Basic thread functions(2)

Wait for termination of another thread#include <pthread.h>int pthread_join(pthread_t th, void **thread_return);

Put a running thread in the detached stateint pthread_detach(pthread_t th);

Thread synchronization

用信号量进行同步 用互斥量进行同步 用条件变量进行同步

POSIX4 semaphore

#include <semaphore.h>

int sem_init(sem_t *sem, int pshared, unsigned int value);

int sem_wait(sem_t *sem);int sem_post(sem_t *sem);int sem_destroy(sem_t *sem);

int sem_trywait(sem_t *sem);int sem_getvalue(sem_t *sem, int *sval);

Example

Producer-consumer problem thread4.c, thread4a.c (in Ch11, BLP)

Mutex (Mutual Exclusion)#include <pthread.h>

int pthread_mutex_init(pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr);

int pthread_mutex_lock(pthread_mutex_t *mutex);int pthread_mutex_unlock(pthread_mutex_t *mutex);int pthread_mutex_destroy(pthread_mutex_t *mutex);

int pthread_mutex_trylock(pthread_mutex_t *mutex);

Example

thread5.c

Thread attributes

线程属性对象 pthread_attr_t

初始化#include <pthread.h>int pthread_attr_init(pthread_attr_t *attr);

get/set族函数

Get/Set thread attributes

#include <pthread.h>int pthread_attr_setdetachstate(pthread_attr_t *attr, int de

tachstate);int pthread_attr_getdetachstate(const pthread_attr_t *attr,

int *detachstate);int pthread_attr_setschedpolicy(pthread_attr_t *attr, int po

licy);int pthread_attr_getschedpolicy(const pthread_attr_t *attr,

int *policy);int pthread_attr_setschedparam(pthread_attr_t *attr, int p

aram);int pthread_attr_getschedparam(const pthread_attr_t *attr,

int *param);

Example(1): 线程属性－分离线程 detachstate属性

Values: PTHREAD_CREATE_JOIN / PTHREAD_CREATE

_DETACHED thread6.c

Example(2): 线程属性－调度 schedpolicy属性

调度策略 Values:

SCHED_OTHER/SCHED_RR/SCHED_FIFO schedparam属性

调度参数，主要是优先级 thread7a.c

Thread cancellation

#include <pthread.h>int pthread_cancel(pthread_t thread);int pthread_setcancelstate(int state, int *oldstate);int pthread_setcanceltype(int type, int *oldtype);

Multithread program

Examples: thread9.c, thread9a.c (in BLP)

Review