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Topic: Shared memory

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	IPC:Shared Memory
		Solaris 2.x also supports System V shared memory, which is another way to let multiple processes attach a segment of physical memory to their virtual address spaces.
		A shared memory segment is described by a control structure with a unique ID that points to an area of physical memory.
		Whether to share memory or to share data contained in the file, when multiple process map a file simultaneously there may be problems with simultaneous access to data elements.
	www.cs.cf.ac.uk /Dave/C/node27.html (3342 words)

	Shared memory - Wikipedia, the free encyclopedia
		The alternatives to shared memory are distributed memory and distributed shared memory, with another, similar set of issues.
		In this context, shared memory is used to facilitate inter-process communication.
		The alternative to shared memory is message passing.
	en.wikipedia.org /wiki/Shared_memory (264 words)

	Configuring Shared Memory on Mac OS X
		The default configuration for shared memory on a Mac is best described as "minimal", and is the same on every Mac, regardless of the amount of total memory or the number of processors.
		Once the shared memory system has been initiallized it is not possible to change the shared memory configuration[1].
		To change the shared memory settings you need to be comfortable with creating and editing files using a text editor such as Emacs, vi, or pico.
	www.spy-hill.net /help/apple/SharedMemory.html (658 words)

	Use shared objects on Linux
		Shared memory is simultaneously mapped to the address space of more than one process: a process simply attaches to the shared memory and starts communicating with other processes by using it as it would use ordinary memory.
		Shared objects also reside in shared memory, and although such objects "belong" to the process that created them, all processes on the system can access them.
		Shared memory is created if it does not exist, and shared objects are created within it.
	www-128.ibm.com /developerworks/linux/library/l-shared.html (1586 words)

	Tutorial - SysV Shared Memory (Site not responding. Last check: 2007-10-11)
		When using shared memory the use of semaphores to protect user processes from accessing data in an intermediate state is almost always necessary.
		The function shmget returns a descriptor for a shared memory segment, but in order to use this segment it must be attached to the process address space used by the running process.
		Shared memory is the fastest form of IPC available to the Unix applications programmer.
	kt.squeakydolphin.com /sysv_shared_mem.jsp (1491 words)

	Shared memory uncovered - SunWorld - September 1997
		As the name implies, shared memory is exactly that; the sharing of the same physical RAM pages by multiple processes, such that each process has mappings to the same physical pages and can access the memory through pointer dereferencing in code.
		Shared memory is a powerful and relatively simple way to share data between processes.
		Intimate shared memory is an important optimization that makes more efficient use of the kernel and hardware resources involved in the implementation of virtual memory and provides a means of keeping heavily used shared pages locked in memory.
	sunsite.uakom.sk /sunworldonline/swol-09-1997/swol-09-insidesolaris.html (3538 words)

	What is Shared Video Memory? Dedicated Card Physical Memory (Site not responding. Last check: 2007-10-11)
		Shared video memory: On lower end systems, the video is integrated into the motherboard.
		When you go out to purchase a computer, some models specify that they have a certain amount of megabytes of memory, and they may have a videocard that supports a certain amount of *shared* memory.
		Thus, if you buy a laptop with 32 megs of memoryand 8 megs of shared memoryand you frequently use a high display pixel depth and/or number of colors, you may actually only have 24 megs of physical memoryavailable left to your computer.
	bugclub.org /beginners/memory/ShareVidMem.html (302 words)

	Shared Memory definition (Phone Scoop)
		Shared (dynamic) memory means that there is one large "pool" of memory available for multiple types of information.
		The disadvantage of partitioned memory is that if you fill up the photo memory, for example, you can't take any more photos until you delete some, even though there may be plenty of (wasted) memory available for other types of info.
		Some phones have a sort of hybrid memory, where some types of info share memory, such as ringtones, wallpaper, and software, while memory for photos and contacts are partitioned, for example.
	www.phonescoop.com /glossary/term.php?gid=238 (223 words)

	MIT-SHM -- The MIT Shared Memory Extension
		Shared memory pixmaps can only be supported when the X server can use regular virtual memory for pixmap data; if the pixmaps are stored in some magic graphics hardware, your application will not be able to share them with the server.
		If you modify the shared memory segment before the arrival of the completion event, the results you see on the screen may be inconsistent.
		Shared memory pixmaps are destroyed in the usual manner with XFreePixmap, though you should detach and destroy the shared memory segment itself as shown above.
	pantransit.reptiles.org /prog/mit-shm.html (1630 words)

	Lecture 15 (Site not responding. Last check: 2007-10-11)
		The desired for a shared memory model arises from the desire to preserve the sequential model of programming, so it is only natural to also impose sequential semantics on writable shared values.
		In a system where memory is a shared resource and processors have only cache as local memory, then each bank of main memory can keep a directory of all caches that have copied a particular line (block).
		The memory must keep a bit-vector for each line that has one bit per processor, plus a bit to indicate ownership (in which case there is only one bit set in the processor vector).
	www.cs.umass.edu /~weems/CmpSci635/635lecture15.html (3561 words)

	Distributed Shared Memory Home Pages (Site not responding. Last check: 2007-10-11)
		Page-based distributed shared memory is similar to the virtual memory mechanism of an operating system except that the pages may exist across a network of machines (in a distributed operating system the virtual memory mechanism and page-based distributed shared memory may be one and the same).
		An advantage of page-based distributed shared memory is that memory access is completely seamless, the user simply accesses the address of memory and the page is automatically swapped in.
		A flexible shared memory allocation call is provided to allow the programmer to control the distribution of shared locations.
	www.cs.utexas.edu /users/kistler/dsm/dsm_links.htm (5710 words)

	Applied Reading - ©2002 Josh Walker (Site not responding. Last check: 2007-10-11)
		Shared memory, on the other hand, is basically a free-form medium, and I was pretty confident that it would be fast enough, so I started the implementation based on shared memory
		Shared memory is what the name implies; it is a portion of address space that is shared between processes.
		When two processes attach the same shared memory segment, they are telling the operating system to relax the normal restrictions by mapping a portion of their address space onto the same memory.
	home.earthlink.net /~joshwalker1/writing/SharedMemory.html (3159 words)

	NSPR Reference: Chapter 28 Named Shared Memory
		Shared memory allows multiple processes to access one or more common shared memory regions, using it as an interprocess communication channel.
		The Unix implementation may use SysV IPC shared memory, Posix shared memory, or memory mapped files; the filename may be used to define the namespace.
		The address to which the shared memory segment is mapped.
	www.mozilla.org /projects/nspr/reference/html/prshm.html (611 words)

	POSIX FIFO and Shared Memory - fsmlabs.com (Site not responding. Last check: 2007-10-11)
		Support for shared memory has been handled in the GPL version of RTLinux using Tomasz Motylewski's mbuff driver for some time.
		As you have probably noticed, we have a file descriptor to a device that has been registered but we haven't specified how much memory is to be used.
		Destroying shared memory is handled through shm_unlink(), as demonstrated in Fig.
	www.fsmlabs.com /posix-fifo-and-shared-memory-8.html (647 words)

	Shared Memory - SarWiki
		However, sometimes it is necessary for processes to share memory.
		Sharing memory for two processes means that there is a region of memory which both processes can access (read/write) such that both processes see the same contents of that memory.
		In systems implementing the Win32 API, shared memory is implemented by use of Memory Mapped Files (MMFs, sometimes also called Sections).
	sarwiki.informatik.hu-berlin.de /Shared_Memory (274 words)

	Distributed shared memory - Wikipedia, the free encyclopedia
		Distributed Shared Memory (DSM), in computer science, refers to a wide class of software and hardware implementations, in which each node of a cluster has access to a large shared memory in addition to each node's limited non-shared private memory.
		In contrast, the object based approach organises the shared memory region as an abstract space for storing sharable objects of variable sizes.
		Shared memory architecture may involve separating memory into shared parts distributed amongst nodes and main memory; or distributing all memory between nodes.
	en.wikipedia.org /wiki/Distributed_shared_memory (254 words)

	Shared Memory Through Memory-Mapped Files
		First the code calls CreateFileMapping to create a read-write memory mapping that is 65,535 bytes in length, with the name passed in the Create method.
		In your own shared memory classes, you can initialize and organize the data anyway you like as long as everyone who uses the data knows the convention.
		A shared memory mapping is destroyed only when all of its clients have unmapped it.
	vb.mvps.org /hardcore/html/sharedmemorythroughmemory-mappedfiles.htm (1090 words)

	LWN: Improving shared memory performance
		Linux has long avoided copying the memory itself; anything which cannot be shared is simply marked "copy on write" and left in place until one process or the other does something to force a particular page to be copied.
		Recently, Ray Fucillo noted that the amount of time required to create a new process increased notably with the size of any shared memory segments that process was using.
		Shared page tables should also help in that regard, but, unlike the copying patch (which may hurt ongoing performance slightly until the page tables are populated), shared page tables speed things up throughout the life of the process.
	lwn.net /Articles/149888 (725 words)

	Shared Memory
		It is the creator of the shared memory that controls the access permissions to that memory and whether its key is public or private.
		So, the first process that accesses a page of the shared memory causes it to be created and thereafter access by the other processes cause that page to be added into their virtual address spaces.
		In this case the pagse of the shared memory may be swapped out to the system's swap disk during periods of high memory usage.
	www.science.unitn.it /~fiorella/guidelinux/tlk/node59.html (612 words)

	shared memory - a definition from Whatis.com
		In computer programming, shared memory is a method by which program processes can exchange data more quickly than by reading and writing using the regular operating system services.
		Using a designated area of shared memory, the data can be made directly accessible to both processes without having to use the system services.
		To put the data in shared memory, the client gets access to shared memory after checking a semaphore value, writes the data, and then resets the semaphore to signal to the server (which periodically checks shared memory for possible input) that data is waiting.
	whatis.techtarget.com /definition/0,,sid9_gci212976,00.html (251 words)

	Shared Memory
		The goal of our research is to investigate how to build efficient shared virtual memory on PC and SMP-based clusters by leveraging simple hardware support, lazy protocols, consistency models, memory-mapped communication and application study.
		This is a simple memory-mapped communication mechanism supported by the SHRIMP network interface, in which local writes are forwarded to a remote node's memory in a transparent manner.
		Shared pages are mapped write-through in the caches so that writes appear on the memory bus.
	www.cs.princeton.edu /shrimp/html/shared_memory.html (327 words)

	SGI - Products: Servers and Supercomputers: SGI Altix: Global Shared Memory
		Most PC users have learned already that they have more to gain by adding memory in their systems than by adding compute power—this is even more true in supercomputing.
		Systems with global shared memory allow access to all data in the system's memory directly and efficiently, without having to move data through I/O or networking bottlenecks.
		To overcome this, clusters without global shared memory must instead pass copies of data, often in the form of messages, which can greatly complicate programming and slow down performance by increasing the time processors must wait for data.
	www.sgi.com /products/servers/altix/memory.html (261 words)

	PHP: Shared Memory Functions - Manual
		But when we step it up a level to 10000 and 40000 files, it becomes pretty obvious that Shared Memory is a better contender.
		So correct me if I'm wrong, but the shmop.c extension uses memcpy() to copy strings to and from shared memory without any form of locking, and as far as I know, memcpy() is not atomic.
		So basically, the purpose of shmop is to provide a symple interface to shared memory that can be used with OTHER NON php shm creators.
	www.php.net /manual/en/ref.shmop.php (944 words)

	SGI - Developer Central: Developing on SGI: Global Shared Memory
		Global shared memory means that a single memory address space is visible to all system resources, including microprocessors and I/O, across all system partitions.
		Systems with global shared memory allow access to all data in the system's memory directly and quickly, without having to go through I/O bottlenecks.
		Systems with multiple nodes without global shared memory instead must pass copies of data, often in the form of messages, which can greatly complicate programming and slow down performance by significantly increasing the time processors must wait for data.
	www.sgi.com /developers/technology/gsm.html (730 words)

	PHP: Semaphore, Shared Memory and IPC Functions - Manual
		Shared memory may be used to provide access to global variables.
		A possible solution is to build a shared mem pool and store there the current number of locks for a semaphore id.
		Shared Memory blocks has the same permission semantics as unix user/group/other file permissions.
	www.php.net /manual/en/ref.sem.php (1223 words)

	Shared Memory Paradigm
		The shared memory paradigm is really restricted to shared memory systems, SMPs , although it is possible to simulate it on distributed memory systems too, albeit not without some cost.
		A process that wants to write on a shared memory location or that wants to read from it, can lock it, so that no other process can access it for writing at the same time.
		Data parallel programming can be implemented on top of shared memory too, with multiple processors of an SMP taking care of separate chunks of arrays that reside in shared memory.
	beige.ucs.indiana.edu /I590/node14.html (372 words)

	PHP Classes - Class: IPC Shared Memory
		Using shared memory is a solution for exchanging information between two or more processes or programs, that may or may not be running at the same time, in the same computer or even in different computers.
		Depending on the requirements of the applications that can benefit from its use, shared memory can be implemented using for instance OS specific shared memory extensions, memory mapped files and database accessible remotely via a network.
		The interface has functions for atomically fetching or storing shared memory data and also functions to start or finish transactions that allow multiple read or write access operations to be safely execute assuring the necessary integrity.
	www.phpclasses.org /browse/package/2059.html (305 words)

	Tuning and Optimizing RHEL for Oracle 9i and 10g Databases (Red Hat Enterprise Linux, 4, 3, 2.1 - redhat, x86-64)
		To increase the space for shared memory in RHEL 2.1, the mapped base for shared libraries for the Oracle processes must be changed by root.
		Shared memory filesystems for the SGA are covered at Configuring Very Large Memory (VLM).
		This memory area is needed for mapping the indirect data buffers (shared memory filesystem buffers) into the process address space since a process cannot attach to more than 4GB directly on a 32-bit system.
	www.puschitz.com /TuningLinuxForOracle.shtml (13503 words)

	Shared Memory Segments
		The cool thing about shared memory segments is that they are what they sound like: a segment of memory that is shared between processes.
		You have the pointer to the shared memory segment!
		Semaphores to lock the shared memory segment while a process is writing to it.
	www.ecst.csuchico.edu /~beej/guide/ipc/shmem.html (1039 words)

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