HP-UX Reference (11i v1 00/12) - 1M System Administration Commands N-Z (vol 4)

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setmemwindow(1M) setmemwindow(1M)

-j Join an existing window with id WinId . The speciﬁed process attaches to an existing memory

window. If no entry exists the call fails.

-n If program is exec’ed, the default behavior is to waitpid (see the wait(2) manual page) for

the process to terminate. Specifying -n causes setmemwindow to exit after fork’ing the

child (that will exec program).

-f The default behavior for setmemwindow is to exit without executing the user speciﬁed pro-

gram if the memory window cannot be set. The failure to set the memory window may be

caused by the lack of enough memory windows in the system, the memory windows feature is

not implemented, a memory window with WinId could not be found in the attempt to join a

memory window, or a memory window with the WinId was found in the attempt to create a

memory window. The -f option instructs setmemwindow to exec program regardless if the

desired memory window was set or not. Obviously, using this option there is no guarantee

program has been attached to the desired memory window and it is unclear in what memory

window it is running. Using this option is strongly discouraged.

-b Create a memory window where both memory window quadrants use the same space id. For

SHMEM_MAGIC executables this generates two quadrants with the same space id. Applica-

tions can use this to generate the appearance of larger contiguous shared memory ranges with

a maximum of 2 gigabytes. For example, an application that generates a 1 gigabyte shared

memory segment has that segment placed into the 2nd quadrant by default. If the application

creates another 1 gigabyte segment that segment is placed in the 3rd quadrant. Both seg-

ments are contiguous virtually, allowing the application to treat the virtual range as if it were

a contiguous 2 gigabyte segment.

This option only beneﬁts SHMEM_MAGIC executables. They are the only type of executable

format able to place shared objects in the 2nd quadrant.

-o Send the pid of the exec’ed program to the stdout. The message sent out is:

"setmemwindow:pid=dddd\n", where dddd is the decimal value of the pid.

Application Usage

Memory Windows helps alleviate the 1.75 gigabytes limitation on system wide shared memory for 32-bit

applications by allowing cooperating applications to conﬁgure their own 1 gigabyte window of shared

resources.

The deﬁnition of a memory window is only available for 32-bit processes.

Note that memory windows allows the creation of more than 1.75 gigabytes of total system wide shared

memory, but it does not extend how much shared memory a single process can create.

SHARED_MAGIC

executables are still limited to 1.75 gigabytes.

HP-UX ships memory windows disabled. To enable memory windows, the kernel tunable parameter,

max_mem_window, must be set to the desired number.

max_mem_window represents the number of

memory windows beyond the global default window. Setting

max_mem_window to 2, for example, would

produce a total of three memory windows, the default global window plus two user deﬁned windows. Set-

ting max_mem_window to 0 leaves only the default or global memory window.

There are two new commands and one ﬁle introduced by memory windows: setmemwindow , get-

memwindow

, and /etc/services.window

ﬁle.

The

/etc/services.window

ﬁle maps a memory window application to a particular window id.

Using this central ﬁle allows applications to share memory windows, by using the same window id, as well

as avoid unintentional memory window collisions. See services.window(4) for more information.

The

getmemwindow command is used to extract the window id of a user process from the

/etc/services.window ﬁle. The setmemwindow command starts a particular process in a

memory window. A common usage of these commands is to extract a memory window id with get-

memwindow

, which is then passed to setmemwindow to start a process with the given window id.

Processes must be in the same window to share data. Processes wanting to share global data, such as

shared memory or MAP_SHARED memory mapped ﬁles, must make sure all processes are in the same

memory window. If processes in different memory windows wish to share data reliably, the creator of the

data must take steps to guarantee the data is placed in a location accessible to all processes.

For more detailed information on memory windows, refer to the 11.0 Memory Window White Paper.

Section 1M−−788 − 2 − HP-UX Release 11i: December 2000

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