Inter-process communication (IPC) can be defined as set of techniques used for exchanging data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods can divided into methods for message passing, synchronization, shared memory, and remote procedure calls (RPC).
Reasons for allowing two processes to communicate with each other may be different :
This document is a Mac OS X manual page. Manual pages are a command-line technology for providing documentation. You can view these manual pages locally using the man(1) command. These manual pages come from many different sources, and thus, have a variety of writing styles. To make OS X memory analysis further difficult, Volatility doesn't maintain a very up to date set of profiles for analysis (not to mention Apple has made it increasingly impossible to easily collect memory from any recent OS X releases). Upgrade the memory of nearly any iMac, MacBook Pro, Mac Pro, or Mac mini. Save money by trading in your original memory chips for a cash rebate.
- Information sharing
- Computational speedup
- Modularity
- Convenience
- Privilege separation
When your Mac is low on memory, blame it on a resource-intensive app such as a graphics editing tool you might be using, or on excessive consumption by a multitude of apps. In this context, it's important to avoid a common misconception: memory (RAM) and disk space are different things. So I ran the command below and it told me the memory limit only was 128 mb. $ php -r 'echo iniget(‘memorylimit').PHPEOL;' Okay, so I just have to change a value in my php.ini file.
In this article we will discuss various techniques available on Mac to accomplish IPC. In the subsequent articles we will see the implementation part for various techniques.
Let's look at the techniques available for IPC one by one.
1. Shared File : Most naive solution where multiple processes will share a common file. It could be a simple .txt file or a .sqlite database. The obvious problems in this method are
- Clients need to continuously poll to see if server has written something in the file.
- Write problems if multiple processes are trying to write to the shared file at the same time.
2. Shared Memory : This is another implementation for IPC where a memory section is shared between different processes.In other words process A writes to this memory and B can read from this memory, or vice verse. This is fast and data doesn't have to be copied around. The downside is that it's really difficult to coordinate changes to the shared memory area.
3. Mach Ports :The fundamental services and primitives of the OS X kernel are based on Mach 3.0. Mach 3.0 was originally conceived as a simple, extensible, communications microkernel. It is capable of running as a stand–alone kernel, with other traditional operating-system services such as I/O, file systems, and networking stacks running as user-mode servers.
However, in OS X, Mach is linked with other kernel components into a single kernel address space. This is primarily for performance. It is much faster to make a direct call between linked components than it is to send messages or do remote procedure calls (RPC) between separate tasks. This modular structure results in a more robust and extensible system than a monolithic kernel would allow, without the performance penalty of a pure microkernel.
The only disadvantage is complexity of implementation and less documentation.
4. Sockets : While most TCP/IP connections are established over a network between two different machines, it is also possible to connect two processes running on the same machine without ever touching a network using TCP/IP.
Using TCP/IP sockets for interprocess communication (IPC) is not very different from using them for network communications. In fact, they can be used in exactly the same way.But if the intent is only for local IPC create a socket in the AF_UNIX family to get a socket that's only for local communication and uses more flexible addressing than TCP/IP allows.
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5. Apple Events : These are the only IPC mechanism which is universally supported by GUI applications on Mac OS X for remote control. Operation like opening a telling a application to open a file or to quit etc. can be done using these.
AppleScript is a scripting language built on top of Apple Events which can be used using scripting bridge in a Mac application.
6. Distributed Notifications : A notification center manages the sending and receiving of notifications. It notifies all observers of notifications meeting specific criteria. The notification information is encapsulated in NSNotification objects. Client objects register themselves with the notification center as observers of specific notifications posted by other objects. When an event occurs, an object posts an appropriate notification to the notification center.
Posting a distributed notification is an expensive operation. The notification gets sent to a system wide server that then distributes it to all the processes that have objects registered for distributed notifications. The latency between posting the notification and the notification's arrival in another process is unbounded. In fact, if too many notifications are being posted and the server's queue fills up, notifications can be dropped.
7. Pasteboard : Every time a copy-paste happens between applications, that's IPC happening using pasteboard. Inter-application drag and drop also uses the pasteboard. It is possible to create custom pasteboards which only desired applications can access for passing data back and forth between applications.
Like distributed notifications, pasteboard work by talking to a central pasteboard server using mach ports.
8. Distributed Objects : This mechanism enables a Cocoa application to call an object in a different Cocoa application (or a different thread in the same application). The applications can even be running on different computers on a network.
Distributed objects operates by having the server make public, an object to which other client processes can connect. Once a connection is made, the client process invokes one of the public object's methods as if the object existed in the client process.
Distributed Objects normally runs over mach ports but can also be used with sockets, allowing it to work between computers as well.
Written By: HEM DUTT, Sr. Engineer/Tech Lead (Mac OSX development), Mindfire Solutions
- Related Questions & Answers
- Selected Reading
The Mac OS is a graphical operating system developed by Apple Inc. The tenth version of the Mac OS is the Mac OS X which was launched in 2001.
The structure of the Mac OS X includes multiple layers. The base layer is Darwin which is the Unix core of the system. Next layer is the graphics system which contains Quartz, OpenGL and QuickTime. Then is the application layer which has four components, namely Classic, Carbon, Cocoa and Java. The top layer is Aqua, which is the user interface.
A diagram that demonstrates the structure of Mac OS X is as follows −
Components of the Mac OS X Structure
Details about the different components of the Mac OS X structure as seen in the image above are as follows −
Core OS
The Darwin Core is based on the BSD (Berkeley Software Distribution) version of Unix. Mach is the main part of the Darwin core and it performs operations such as memory use, data flow from and to CPU etc. Darwin is also open source i.e. anyone can obtain its source code and make modifications to it. Different versions of Darwin can be used to enhance the Mac OS X.
Some of the major features of the Darwin core are protected memory, automatic memory management, preemptive multitasking, advanced virtual memory etc. It also provides I/O services for Mac OS X and supports plug-and-play, hot-swapping and power management.
Graphics Subsystem
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The graphics subsystem in the Mac OS X contains three parts i.e. Quartz, OpenGL and QuickTime. The 2-D graphics in the graphics subsystem is managed by Quartz. It provides fonts, interface graphics, rendering of the images etc. OpenGL provides support for 3-D graphics in the system such as texture mapping, transparency, antialiasing, atmospheric effects, special effects etc.
It is also used in Unix and Windows systems. QuickTime is used for different digital media such as digital video, audio and video streaming etc. It also enables creative applications such as iMovie, iTunes etc.
Application Subsystem
AppleScript is a scripting language built on top of Apple Events which can be used using scripting bridge in a Mac application.
6. Distributed Notifications : A notification center manages the sending and receiving of notifications. It notifies all observers of notifications meeting specific criteria. The notification information is encapsulated in NSNotification objects. Client objects register themselves with the notification center as observers of specific notifications posted by other objects. When an event occurs, an object posts an appropriate notification to the notification center.
Posting a distributed notification is an expensive operation. The notification gets sent to a system wide server that then distributes it to all the processes that have objects registered for distributed notifications. The latency between posting the notification and the notification's arrival in another process is unbounded. In fact, if too many notifications are being posted and the server's queue fills up, notifications can be dropped.
7. Pasteboard : Every time a copy-paste happens between applications, that's IPC happening using pasteboard. Inter-application drag and drop also uses the pasteboard. It is possible to create custom pasteboards which only desired applications can access for passing data back and forth between applications.
Like distributed notifications, pasteboard work by talking to a central pasteboard server using mach ports.
8. Distributed Objects : This mechanism enables a Cocoa application to call an object in a different Cocoa application (or a different thread in the same application). The applications can even be running on different computers on a network.
Distributed objects operates by having the server make public, an object to which other client processes can connect. Once a connection is made, the client process invokes one of the public object's methods as if the object existed in the client process.
Distributed Objects normally runs over mach ports but can also be used with sockets, allowing it to work between computers as well.
Written By: HEM DUTT, Sr. Engineer/Tech Lead (Mac OSX development), Mindfire Solutions
- Related Questions & Answers
- Selected Reading
The Mac OS is a graphical operating system developed by Apple Inc. The tenth version of the Mac OS is the Mac OS X which was launched in 2001.
The structure of the Mac OS X includes multiple layers. The base layer is Darwin which is the Unix core of the system. Next layer is the graphics system which contains Quartz, OpenGL and QuickTime. Then is the application layer which has four components, namely Classic, Carbon, Cocoa and Java. The top layer is Aqua, which is the user interface.
A diagram that demonstrates the structure of Mac OS X is as follows −
Components of the Mac OS X Structure
Details about the different components of the Mac OS X structure as seen in the image above are as follows −
Core OS
The Darwin Core is based on the BSD (Berkeley Software Distribution) version of Unix. Mach is the main part of the Darwin core and it performs operations such as memory use, data flow from and to CPU etc. Darwin is also open source i.e. anyone can obtain its source code and make modifications to it. Different versions of Darwin can be used to enhance the Mac OS X.
Some of the major features of the Darwin core are protected memory, automatic memory management, preemptive multitasking, advanced virtual memory etc. It also provides I/O services for Mac OS X and supports plug-and-play, hot-swapping and power management.
Graphics Subsystem
The Memory Of Tennis Mac Os X
The graphics subsystem in the Mac OS X contains three parts i.e. Quartz, OpenGL and QuickTime. The 2-D graphics in the graphics subsystem is managed by Quartz. It provides fonts, interface graphics, rendering of the images etc. OpenGL provides support for 3-D graphics in the system such as texture mapping, transparency, antialiasing, atmospheric effects, special effects etc.
It is also used in Unix and Windows systems. QuickTime is used for different digital media such as digital video, audio and video streaming etc. It also enables creative applications such as iMovie, iTunes etc.
Application Subsystem
The application subsystem in Mac OS X provides the classic environment to run classic applications. Carbon, Cocoa and Java are the three application development environments available. Loss of fluid mac os.
The classic environment makes sure that applications written for the previous versions of the operating system can run smoothly. The carbon environment is used to port existing applications to carbon application program interfaces. This is called carbonising the application. The cocoa environment provides object-oriented application development environment. The cocoa applications use the benefits of the Mac OS X Structure the most. The Java applications and Java applets can be run using the Java environment.
User Interface
Aqua is the user interface of Mac OS X. It provides good visual features as well as the tools to customize the user interface as per the user requirements. Dont explode (itch) (jambonsupreme) mac os. Aqua contains extensive use of colour and texture as well as extremely detailed icons. It is both pleasant to view and efficient to use.
