IPC: -IPC Mechanisms

This example demonstrates how a parent process communicates with its child -process using various IPC mechanisms. Two executables, a parent and a child -(spawned by the parent) are created to demonstrate these mechanisms. The child -process is created by the parent using the posix_spawn() function. -The parent process communicates with the child process using the following -IPC mechanisms:

Named pipes (FIFO - -First in First Out)
Single pipe (popen() system -call)

Download

Click on the following link to download -the example: IPC.zip

Click: browse to view the example code.

Description

Spawning the child process

The posix_spawn() function -creates the child process. A pointer to the process ID (pid) -of the child process and the path of the child process are passed as arguments -to this function. The parent waits for the child to terminate by calling the waitpid() function.

Creating -a named pipe

This example creates a named pipe using the mkfifo() function. -The child writes data into the FIFO and then exits. The parent reads data -from FIFO and writes it to the console. The first argument of the mkfifo() function -indicates the path of the FIFO file.

Opening a single pipe

The -parent creates a child process and a pipe to the child process using the popen() function. -A file handle to the pipe is returned to the parent and the parent uses this -handle to read the data written to the pipe by the child. The path of the -child process is passed as the first argument to the popen() function.

Build

The following statements are present in all -the .mmp files of the example:

SYSTEMINCLUDE epoc32\include\stdapis -LIBRARY libc.lib -STATICLIBRARY libcrt0.lib

Note: You require these statements -because of the following reasons:

The epoc32\include\stdapis directory -contains header files such as, stdio.h, unistd.h and -so on that are required to build an Open Environment application.
The libc.lib file -contains the definitions of all functions that are defined in the header files -associated with this example.
The libcrt0.lib file -provides the E32Main() function, which is the entry point -for the main() function of the example.

The Symbian -OS build process describes how to build this example. The IPC builds -the following binaries in the standard location (\epoc32\release\winscw\<build_variant> for -Carbide.c++).

ipcparent.exe: Executable -of the parent process.
ipcchild.exe: Executable -of the child process created using the popen() function.
fifochild.exe: Executable -of the child process created using the posix_spawn() function.

Runtime setting

Two eshells must be opened before -executing this example. The executable, ipcparent.exe is -run in one eshell and the other eshell is used to run the child process fifochild.exe. -You can switch between the two eshells by pressing CTRL +ALT +SHIFT +T.

+ + + + + +IPC: +IPC Mechanisms +

This example demonstrates how a parent process communicates with its child +process using various IPC mechanisms. Two executables, a parent and a child +(spawned by the parent) are created to demonstrate these mechanisms. The child +process is created by the parent using the posix_spawn() function. +The parent process communicates with the child process using the following +IPC mechanisms:

Named pipes (FIFO - +First in First Out)
Single pipe (popen() system +call)

Download

Click on the following link to download +the example: IPC.zip

Click: browse to view the example code.

Description

Spawning the child process

The posix_spawn() function +creates the child process. A pointer to the process ID (pid) +of the child process and the path of the child process are passed as arguments +to this function. The parent waits for the child to terminate by calling the waitpid() function.

Creating +a named pipe

This example creates a named pipe using the mkfifo() function. +The child writes data into the FIFO and then exits. The parent reads data +from FIFO and writes it to the console. The first argument of the mkfifo() function +indicates the path of the FIFO file.

Opening a single pipe

The +parent creates a child process and a pipe to the child process using the popen() function. +A file handle to the pipe is returned to the parent and the parent uses this +handle to read the data written to the pipe by the child. The path of the +child process is passed as the first argument to the popen() function.

Build

The following statements are present in all +the .mmp files of the example:

SYSTEMINCLUDE epoc32\include\stdapis +LIBRARY libc.lib +STATICLIBRARY libcrt0.lib

Note: You require these statements +because of the following reasons:

The epoc32\include\stdapis directory +contains header files such as, stdio.h, unistd.h and +so on that are required to build an Open Environment application.
The libc.lib file +contains the definitions of all functions that are defined in the header files +associated with this example.
The libcrt0.lib file +provides the E32Main() function, which is the entry point +for the main() function of the example.

The Symbian +OS build process describes how to build this example. The IPC builds +the following binaries in the standard location (\epoc32\release\winscw\<build_variant> for +Carbide.c++).

ipcparent.exe: Executable +of the parent process.
ipcchild.exe: Executable +of the child process created using the popen() function.
fifochild.exe: Executable +of the child process created using the posix_spawn() function.

Runtime setting

Two eshells must be opened before +executing this example. The executable, ipcparent.exe is +run in one eshell and the other eshell is used to run the child process fifochild.exe. +You can switch between the two eshells by pressing CTRL +ALT +SHIFT +T.

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