Posix Programming How to way create a process, child process, multiple child process., thread., multiple threads, , message, message send, message receive

Posix Programming

1) How to way create a process.

2) How to way create a child process.

3) How to way create a multi-child process.

4) How to way create a thread.

5) How to way create a multithread.

6) How to way create a message Queue create.

7) How to way create a message send.

8) How to way create a message received.

Problem 1. How to create a process.

Code in the figure. 1 shows how to create a process.

Fig 1. Process create.

Description: The compiling output of the code in figure. 1 is

$ gcc –o createprocess problem0.c

./createprocess

Output:

Figure. Output of create process

The output of ps command

$ ps – afx | grep createprocess

Figure. Ps command of create process

This program we use some building functions.

getppid() and getpid() are inbuilt functions defined in unistd.h librar.

(*) fork()

System call fork() is used to create processes. It takes no arguments and returns a process ID. The purpose of fork() is to create a new process

If fork() returns a negative value, the creation of a child process was unsuccessful.
fork() returns a zero to the newly created child process.

fork() returns a positive value, the process ID of the child process, to the parent. The returned process ID is of type pid_t defined in sys/types.h. Normally, the process ID is an integer. Moreover, a process can use function getpid() to retrieve the process ID assigned to this process.

(*) getppid() :

returns the process ID of the parent of the calling process. If the calling process was created by the fork() function and the parent process still exists at the time of the getppid function call, this function returns the process ID of the parent process. Otherwise, this function returns a value of 1 which is the process id for initprocess.

pid_t getppid(void);

Return type: getppid() returns the process ID of the parent of the current process. It never throws any error therefore is always successful.

(*) getpid() :

returns the process ID of the calling process. This is often used by routines that generate unique temporary filenames. Syntax: pid_t getpid(void);

Return type: getpid() returns the process ID of the current process. It never throws any error therefore is always successful.

(*) gid) and uid()

In a Unix system, a GID (group ID) is a name that associates a system user with other users sharing something in common (perhaps a work project or a department name). It's often used for accounting purposes. A user can be a member of more than one group and thus have more than one GID. Any user using a UNIX system at a given time has both a user ID (UID) and a group ID (GID).

Problem 2. How to create a child process

Code in the figure. 2 shows how to create a child process

Figure 2. Child process code

Description: The compiling output of the code in figure 2 is

$ gcc –o childcreate problem1.c

./childcreate

Output:

Figure. Output of child process

The output of ps command $ps –afx | grep createchild

Figure. Ps command of Create child

(*) fork()

System call fork() is used to create processes. It takes no arguments and returns a process ID. The purpose of fork() is to create a new process

If fork() returns a negative value, the creation of a child process was unsuccessful.
fork() returns a zero to the newly created child process.
fork() returns a positive value, the process ID of the child process, to the parent. The returned process ID is of type pid_t defined in sys/types.h. Normally, the process ID is an integer. Moreover, a process can use function getpid() to retrieve the process ID assigned to this process.

Problem 3. How to create multiple child process.

Code in the figure. 3 shows how to create multiple child process

Figure 3. Multi child process code

Description: The compiling output of the code in figure 3 is

$gcc –o multiprocess problem2.c

./multiprocess

Output:

Figure. Multi child process output

The output of ps command $ps –afx | grep multiprocess

Figure. Ps command of multichild process

(*) fork()

System call fork() is used to create processes. It takes no arguments and returns a process ID. The purpose of fork() is to create a new process

If fork() returns a negative value, the creation of a child process was unsuccessful.
fork() returns a zero to the newly created child process.
fork() returns a positive value, the process ID of the child process, to the parent. The returned process ID is of type pid_t defined in sys/types.h. Normally, the process ID is an integer. Moreover, a process can use function getpid() to retrieve the process ID assigned to this process.

Problem 4. How to create a thread.

Code in the figure. 4 shows how to create a thread.

Figure 4. Thread code

Description: The compiling output of the code in figure 4 is

$gcc –o thread thread.c -lpthread

./thread

Output:

Figure. Output of thread

The output of ps command $ps –afx | grep thread

Figure. Ps command of thread

NAME

pthread_create - create a new thread

SYNOPSIS

#include <pthread.h> int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine)(void*), void *arg);

NAME

pthread_join - join with a terminated thread

SYNOPSIS

#include <pthread.h> int pthread_join(pthread_t thread, void **retval); Compile and link with -pthread.

Problem 5. How to create multiple threads

Code in the figure 5 shows how to create a multiple thread.

Figure 5. Multiple thread code

Description: The compiling output of the code in figure 5 is

$gcc –o multithread multithread.c –lpthread

./multithread

Output:

Figure. Multi thread output

The output of ps command $ps –afx | grep multithread

Figure. Ps command of multithread

NAME

pthread_create - create a new thread

SYNOPSIS

#include <pthread.h> int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine)(void*), void *arg);

NAME

pthread_join - join with a terminated thread

SYNOPSIS

#include <pthread.h> int pthread_join(pthread_t thread, void **retval); Compile and link with -pthread.

Problem 6. How to create a message

Code in the figure 6 shows how to create a message

Figure 6. Message create code

Description: the compiling output of the code in figure 6 is

$gcc –o msgcreate createmessageQueue.c

./msgcreate

Output:

Figure. Message queue

The output of ipcs –q command for message

Figure. Ipcs –q command of message create.

NAME

msgget - get a System V message queue identifier

SYNOPSIS

#include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> int msgget(key_t key, int msgflg);

Problem 7. How to send a message

Code in the figure 7 shows how to send a message

Figure 7. Message send in queue

Description: The compiling output of the code in figure 7 is

$gcc –o msgsend messagesend.c

./msgsend

Output:

Figure. Message sent to queue

The output of ipcs –q of message sent is

Figure. Ipcs –q of sent message

NAME

msgget - get a System V message queue identifier

SYNOPSIS

#include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> int msgget(key_t key, int msgflg);

Problem 8. How to receive a message

Code in the figure 8 shows how to receive a message

Figure 8. Message receive

Description:

The compiling output of the code in figure 8 is

$gcc –o msgrcv messagerecv.c

./msgrcv

Output:

Figure. Message receive output

The output of ipcs –q command for this code

Figure. Ipcs –q for message receive

NAME

msgget - get a System V message queue identifier

SYNOPSIS

#include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> int msgget(key_t key, int msgflg);

Special Notes: if we remove previous message queue id then we need to write: ipcrm -q 0( 0 is a process id).