Contexts 3 5 3 – Fast Window Switcher Systems

The search loop needs a small bit of CPU time for every runnable process and needs it on every context switch. The above benchmark shows the context switch times with 40 contexts present and ready to run. That corresponds to a load average of 40 for a single CPU system or 20 for a dual CPU system.

1. Contexts 3 5 3 – Fast Window Switcher Systems Installation
2. Contexts 3 5 3 – Fast Window Switcher Systems Inc
3. Contexts 3 5 3 – Fast Window Switcher Systems Diagram
4. Contexts 3 5 3 – Fast Window Switcher Systems System

• Contexts 3 Radically simpler & faster window switcher Switch between application windows effortlessly — with Fast Search, a better Command-Tab, a Sidebar or even a quick gesture. Includes fantastic features for multiple spaces & multiple displays.
• Windows has to keep track of the thread objects, and every so often, Windows has to decide which thread to schedule next to go to the CPU. This is additional code that has to execute once every 20 milliseconds or so. When Windows makes a CPU stop executing one thread's code and start executing another thread's code, we call this a context switch.

Definition

Provides members for setting and retrieving data about an application's context.

Remarks

The AppContext class enables library writers to provide a uniform opt-out mechanism for new functionality for their users. It establishes a loosely-coupled contract between components in order to communicate an opt-out request. This capability is typically important when a change is made to existing functionality. Conversely, there is already an implicit opt-in for new functionality.

AppContext for library developers

Libraries use the AppContext class to define and expose compatibility switches, while library users can set those switches to affect the library behavior. By default, libraries provide the new functionality, and they only alter it (that is, they provide the previous functionality) if the switch is set. This allows libraries to provide new behavior for an existing API while continuing to support callers who depend on the previous behavior.

Define the switch name

The most common way to allow consumers of your library to opt out of a change of behavior is to define a named switch. Its value element is a name/value pair that consists of the name of a switch and its Boolean value. By default, the switch is always implicitly false, which provides the new behavior (and makes the new behavior opt-in by default). Setting the switch to true enables it, which provides the legacy behavior. Explicitly setting the switch to false also provides the new behavior.

It's beneficial to use a consistent format for switch names, since they are a formal contract exposed by a library. The following are two obvious formats.

• Switch.namespace.switchname

• Switch.library.switchname

Once you define and document the switch, callers can use it by using the registry, by adding an element to their application configuration file, or by calling the AppContext.SetSwitch(String, Boolean) method programmatically. See the AppContext for library consumers section for more information about how callers use and set the value of AppContext configuration switches.

When the common language runtime runs an application, it automatically reads the registry's compatibility settings and loads the application configuration file in order to populate the application's AppContext instance. Because the AppContext instance is populated either programmatically by the caller or by the runtime, you do not have to take any action, such as calling the SetSwitch method, to configure the AppContext instance.

Contexts 3 5 3 – Fast Window Switcher Systems Installation

Check the setting

You can then check if a consumer has declared the value of the switch and act appropriately by calling the AppContext.TryGetSwitch method. The method returns true if the switchName argument is found, and when the method returns, its isEnabled argument indicates the value of the switch. Otherwise, the method returns false.

An example

The following example illustrates the use of the AppContext class to allow the customer to choose the original behavior of a library method. The following is version 1.0 of a library named StringLibrary. It defines a SubstringStartsAt method that performs an ordinal comparison to determine the starting index of a substring within a larger string.

The following example then uses the library to find the starting index of the substring 'archæ' in 'The archaeologist'. Because the method performs an ordinal comparison, the substring cannot be found.

Contexts 3 5 3 – Fast Window Switcher Systems Inc

Version 2 of the library, however, changes the SubstringStartsAt method to use culture-sensitive comparison.

When the app is recompiled to run against the new version of the library, it now reports that the substring 'archæ' is found at index 4 in 'The archaeologist'.

This change can be prevented from breaking the applications that depend on the original behavior by defining an switch. In this case, the switch is named StringLibrary.DoNotUseCultureSensitiveComparison. Its default value, false, indicates that the library should perform its version 2.0 culture-sensitive comparison. true indicates that the library should perform its version 1.0 ordinal comparison. A slight modification of the previous code allows the library consumer to set the switch to determine the kind of comparison the method performs.

If application can then use the following configuration file to restore the version 1.0 behavior.

When the application is run with the configuration file present, it produces the following output:

AppContext for library consumers

If you are the consumer of a library, the AppContext class allows you to take advantage of a library or library method's opt-out mechanism for new functionality. Individual methods of the class library that you are calling define particular switches that enable or disable a new behavior. The value of the switch is a Boolean. If it is false, which is typically the default value, the new behavior is enabled; if it is true, the new behavior is disabled, and the member behaves as it did previously.

You can set the value of a switch in one of four ways:

• By calling the AppContext.SetSwitch(String, Boolean) method in your code. The switchName argument defines the switch name, and the isEnabled property defines the value of the switch. Because AppContext is a static class, it is available on a per-application domain basis.

  Calling the AppContext.SetSwitch(String, Boolean) has application scope; that is, it affects only the application.

• By adding an element to the section of your app.config file. The switch has a single attribute, value, whose value is a string that represents a key/value pair containing both the switch name and its value.

  To define multiple switches, separate each switch's key/value pair in the element's value attribute with a semicolon. In that case, the element has the following format:

  Using the Mac lady danger vs chili. element to define a configuration setting has application scope; that is, it affects only the application.

  Note

  For information on the switches defined by the .NET Framework, see the element.

• By adding an entry to the registry. Add a new string value to the HKLMSOFTWAREMicrosoft.NETFrameworkAppContext subkey. Set the name of the entry to the name of the switch. Set its value to one of the following options: True, true, False, or false. If the runtime encounters any other value, it ignores the switch.

  On a 64-bit operating system, you must also add the same entry to the HKLMSOFTWAREWow6432NodeMicrosoft.NETFrameworkAppContext subkey.

  Using the registry to define an AppContext switch has machine scope; that is, it affects every application running on the machine.

• For ASP.NET applications, you add an element to the section of the web.config file. For example:

If you set the same switch in more than one way, the order of precedence for determining which setting overrides the others is:

1. The programmatic setting.

2. The setting in the app config file or the web.config file.

3. The registry setting.

The following is a simple application that passes a file URI to the Path.GetDirectoryName method. When run under the .NET Framework 4.6, it throws an ArgumentException because file:// is no longer a valid part of a file path.

To restore the method's previous behavior and prevent the exception, you can add the Switch.System.IO.UseLegacyPathHandling switch to the application configuration file for the example:

See also

Properties

Methods

Applies to

See also

What is Context Switching in Operating System?

In the Operating System, there are cases when you have to bring back the process that is in the running state to some other state like ready state or wait/block state. If the running process wants to perform some I/O operation, then you have to remove the process from the running state and then put the process in the I/O queue. Sometimes, the process might be using a round-robin scheduling algorithm where after every fixed time quantum, the process has to come back to the ready state from the running state. So, these process switchings are done with the help of Context Switching. In this blog, we will learn about the concept of Context Switching in the Operating System and we will also learn about the advantages and disadvantages of Context Switching. So, let's get started.

What is Context Switching?

A context switching is a process that involves switching of the CPU from one process or task to another. In this phenomenon, the execution of the process that is present in the running state is suspended by the kernel and another process that is present in the ready state is executed by the CPU.

It is one of the essential features of the multitasking operating system. The processes are switched so fastly that it gives an illusion to the user that all the processes are being executed at the same time.

But the context switching process involved a number of steps that need to be followed. You can't directly switch a process from the running state to the ready state. You have to save the context of that process. If you are not saving the context of any process P then after some time, when the process P comes in the CPU for execution again, then the process will start executing from starting. But in reality, it should continue from that point where it left the CPU in its previous execution. So, the context of the process should be saved before putting any other process in the running state.

A context is the contents of a CPU's registers and program counter at any point in time. Context switching can happen due to the following reasons:

• When a process of high priority comes in the ready state. In this case, the execution of the running process should be stopped and the higher priority process should be given the CPU for execution.
• When an interruption occurs then the process in the running state should be stopped and the CPU should handle the interrupt before doing something else.
• When a transition between the user mode and kernel mode is required then you have to perform the context switching.

Steps involved in Context Switching

The process of context switching involves a number of steps. The following diagram depicts the process of context switching between the two processes P1 and P2.

In the above figure, you can see that initially, the process P1 is in the running state and the process P2 is in the ready state. Now, when some interruption occurs then you have to switch the process P1 from running to the ready state after saving the context and the process P2 from ready to running state. The following steps will be performed:

1. Firstly, the context of the process P1 i.e. the process present in the running state will be saved in the Process Control Block of process P1 i.e. PCB1.
2. Now, you have to move the PCB1 to the relevant queue i.e. ready queue, I/O queue, waiting queue, etc.
3. From the ready state, select the new process that is to be executed i.e. the process P2.
4. Now, update the Process Control Block of process P2 i.e. PCB2 by setting the process state to running. If the process P2 was earlier executed by the CPU, then you can get the position of last executed instruction so that you can resume the execution of P2.
5. Similarly, if you want to execute the process P1 again, then you have to follow the same steps as mentioned above(from step 1 to 4).

For context switching to happen, two processes are at least required in general, and in the case of the round-robin algorithm, you can perform context switching with the help of one process only.

The time involved in the context switching of one process by other is called the Context Switching Time.

Advantage of Context Switching

Context switching is used to achieve multitasking i.e. multiprogramming with time-sharing(learn more about multitasking from here). Multitasking gives an illusion to the users that more than one process are being executed at the same time. But in reality, only one task is being executed at a particular instant of time by a processor. Here, the context switching is so fast that the user feels that the CPU is executing more than one task at the same time.

The disadvantage of Context Switching

See also

What is Context Switching in Operating System?

In the Operating System, there are cases when you have to bring back the process that is in the running state to some other state like ready state or wait/block state. If the running process wants to perform some I/O operation, then you have to remove the process from the running state and then put the process in the I/O queue. Sometimes, the process might be using a round-robin scheduling algorithm where after every fixed time quantum, the process has to come back to the ready state from the running state. So, these process switchings are done with the help of Context Switching. In this blog, we will learn about the concept of Context Switching in the Operating System and we will also learn about the advantages and disadvantages of Context Switching. So, let's get started.

What is Context Switching?

A context switching is a process that involves switching of the CPU from one process or task to another. In this phenomenon, the execution of the process that is present in the running state is suspended by the kernel and another process that is present in the ready state is executed by the CPU.

It is one of the essential features of the multitasking operating system. The processes are switched so fastly that it gives an illusion to the user that all the processes are being executed at the same time.

But the context switching process involved a number of steps that need to be followed. You can't directly switch a process from the running state to the ready state. You have to save the context of that process. If you are not saving the context of any process P then after some time, when the process P comes in the CPU for execution again, then the process will start executing from starting. But in reality, it should continue from that point where it left the CPU in its previous execution. So, the context of the process should be saved before putting any other process in the running state.

A context is the contents of a CPU's registers and program counter at any point in time. Context switching can happen due to the following reasons:

• When a process of high priority comes in the ready state. In this case, the execution of the running process should be stopped and the higher priority process should be given the CPU for execution.
• When an interruption occurs then the process in the running state should be stopped and the CPU should handle the interrupt before doing something else.
• When a transition between the user mode and kernel mode is required then you have to perform the context switching.

Steps involved in Context Switching

The process of context switching involves a number of steps. The following diagram depicts the process of context switching between the two processes P1 and P2.

In the above figure, you can see that initially, the process P1 is in the running state and the process P2 is in the ready state. Now, when some interruption occurs then you have to switch the process P1 from running to the ready state after saving the context and the process P2 from ready to running state. The following steps will be performed:

1. Firstly, the context of the process P1 i.e. the process present in the running state will be saved in the Process Control Block of process P1 i.e. PCB1.
2. Now, you have to move the PCB1 to the relevant queue i.e. ready queue, I/O queue, waiting queue, etc.
3. From the ready state, select the new process that is to be executed i.e. the process P2.
4. Now, update the Process Control Block of process P2 i.e. PCB2 by setting the process state to running. If the process P2 was earlier executed by the CPU, then you can get the position of last executed instruction so that you can resume the execution of P2.
5. Similarly, if you want to execute the process P1 again, then you have to follow the same steps as mentioned above(from step 1 to 4).

For context switching to happen, two processes are at least required in general, and in the case of the round-robin algorithm, you can perform context switching with the help of one process only.

The time involved in the context switching of one process by other is called the Context Switching Time.

Advantage of Context Switching

Context switching is used to achieve multitasking i.e. multiprogramming with time-sharing(learn more about multitasking from here). Multitasking gives an illusion to the users that more than one process are being executed at the same time. But in reality, only one task is being executed at a particular instant of time by a processor. Here, the context switching is so fast that the user feels that the CPU is executing more than one task at the same time.

The disadvantage of Context Switching

The disadvantage of context switching is that it requires some time for context switching i.e. the context switching time. Time is required to save the context of one process that is in the running state and then getting the context of another process that is about to come in the running state. During that time, there is no useful work done by the CPU from the user perspective. So, context switching is pure overhead in this condition.

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Contexts 3 5 3 – Fast Window Switcher Systems Diagram

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