Atomic List Manager Serial

If you remove a field from a configuration and apply the configuration,Server-Side Apply checks if there are any other field managers that alsoown the field. If the field is not owned by any other field managers, itis either deleted from the live object or reset to its default value, ifit has one. The same rule applies to associative list or map items.

When the listType, mapType, or structType changes frommap/set/granular to atomic, the whole list, map, or struct ofexisting objects will end-up being owned by actors who owned an elementof these types. This means that any further change to these objectswould cause a conflict.

Atomic List Manager Serial

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When a list, map, or struct changes from atomic tomap/set/granular, the API server won't be able to infer the newownership of these fields. Because of that, no conflict will be producedwhen objects have these fields updated. For that reason, it is notrecommended to change a type from atomic to map/set/granular.

Before spec.data gets changed from atomic to granular,manager-one owns the field spec.data, and all the fields within it(key1 and key2). When the CRD gets changed to make spec.datagranular, manager-one continues to own the top-level fieldspec.data (meaning no other managers can delete the map called datawithout a conflict), but it no longer owns key1 and key2, so anothermanager can then modify or delete those fields without conflict.

OSTree is designed to implement fully atomic and safe upgrades;more generally, atomic transitions between lists of bootabledeployments. If the system crashes or you pull the power, youwill have either the old system, or the new one.

At a practical level, most package managers today (dpkg and rpm)operate "live" on the currently booted filesystem. The way they couldwork with OSTree is instead to take the list of installed packages inthe currently booted tree, and compute a new filesystem from that. Alater chapter describes in more details how this could work:Adapting Existing Systems.

To support a more general case, OSTree supports atomic transitioningbetween arbitrary sets of deployments, with the restriction that thecurrently booted deployment must always be in the new set. In thenormal case, we have exactly one deployment, which is the booted one,and we want to add the new deployment to the list. A more complexcommand might allow creating 100 deployments as part of one atomictransaction, so that one can set up an automated system to bisectacross them.

There are also atomic operations which return the old or the new value. They follow the atomic_fetch_[op] and atomic_[op]_fetch naming scheme. For example if one would want to find all the indicies of negative values in an array and store them in a list this would be the algorithm:

For example, a single token which matchesNmtoken from[XML 1.0 (Second Edition)] could be the value of an atomicdatatype (NMTOKEN); while a sequence of such tokenscould be the value of a list datatype(NMTOKENS).

list datatypes are always derived.The value space of a listdatatype is a set of finite-length sequences of atomicvalues. The lexical space of alist datatype is a set of literals whose internalstructure is a space-separatedsequence of literals of theatomic datatype of the items in thelist.

A list datatype can be derivedfrom an atomic datatype whoselexical space allows space(such as stringor anyURI)or aunion datatype any of whose member type definitions'slexical space allows space.In such a case, regardless of the input, list itemswill be separated at space boundaries.

If variety is atomicthen the value space of the datatype defined willbe a subset of the value space ofbase type definition (which is a subset of thevalue space of primitive type definition).If variety is listthen the value space of the datatype defined willbe the set of finite-length sequence of values from thevalue space of item type definition.If variety is union then thevalue space of the datatype defined will be theunion of the value spaces of each datatype inmember type definitions.

If variety is atomicthen the variety of base type definitionmust be atomic.If variety is listthen the variety of item type definitionmust be either atomic or union.If variety is unionthenmember type definitions must be a list of datatype definitions.

A list datatype must be derivedfrom an atomic or a union datatype,known as theitemType of the list datatype.This yields a datatype whose value space is composed offinite-length sequences of values from the value space of theitemType and whose lexical space iscomposed of space-separated lists of literals of theitemType.

whiteSpace is applicable to all atomic andlist datatypes. For all atomicdatatypes other than string (and types derivedby restriction from it) the value of whiteSpace iscollapse and cannot be changed by a schema author; forstring the value of whiteSpace ispreserve; for any type derived byrestriction fromstring the value of whiteSpace canbe any of the three legal values. For all datatypesderived by list thevalue of whiteSpace is collapse and cannotbe changed by a schema author. For all datatypesderived by union whiteSpace does not apply directly; however, thenormalization behavior of union types is controlled bythe value of whiteSpace on that one of thememberTypes against which the unionis successfully validated.

In QNX 6, resource managers are responsible for presenting an interface to various types of devices. In other operating systems, the managing of actual hardware devices (e.g. serial ports, parallel ports, network cards, and disk drives)or virtual devices (e.g. /dev/null, a network filesystem, and pseudo-ttys),is associated with device drivers.But unlike device drivers, the QNX 6 resource managers execute as processes separate from the kernel. In fact, a resource manager looks just like any other user-level program. This cannot be understated.Adding resource managers in QNX 6 won't affect any other part of the OS -- the drivers are developed and debugged like any other application. And since the resource managers are in their own protected address space, a bug in a device driver won't cause the entire OS to shut down.

A serial port may be managed by a resource manager called devc-ser8250, although the actual resource may be called /dev/ser1 in the pathname space. When a process requests serial port services, it does so by opening a serial port (in this case /dev/ser1).

For the above example, here's the description of what happened behind the scenes.We'll assume that a serial port is managed by a resource manager called devc-ser8250,that's been registered with the pathname prefix /dev/ser1:

When the client's library issued the query call in step 1, the Process manager looked through all of its tables for any registered pathname prefixes that match the name. Previously, had another resource manager registered the name /, more than one match would be found. So, in this case, both / and /dev/ser1 match. The Process manager will reply to the open() with the list of matched servers or resource managers. The servers are queried in turn about their handling of the path, with the longest match being asked first.

In this example, a serial port may be managed by a resource manager called devc-xxx, but the actual resource is registered as /dev/sample in the pathname space. Therefore, when a program requests serial port services, it opens the /dev/sample serial port.

But let's see what happens in the resource manager when it'shandling these messages. With multiple threads, both of theclient's threads may very well have sent in their"atomic" combine messages. Two threads in theresource manager will now attempt to service those twomessages. We again run into the same synchronization problemas we originally had on the client end -- one threadcan be part way through processing the message and can thenbe preempted by the other thread.

This condition is met when there's one or more units of input data available (i.e. clients can now issue reads). The number of units defaults to 1, but can be changed. The definition of a unit is up to you: for a character device such as a serial port, it would be a character; for a POSIX message queue, it would be a message. Each resource manager selects an appropriate object.

A resource manager needs to keep a list of clients that want to be notified as conditions are met,along with the events to use to do the notifying. When a condition is met, the resource manager must traverse the list to look for clients that are interested in that condition, and then deliver the appropriate event.As well, if a client closes its file descriptor, then any notification entries for that client must be removed from the list. To make all this easier, the following structure and helper functions are provided for you to use in a resource manager:

All Mnesia transactions, including all the schema update functions, either return value atomic, Val or the tuple aborted, Reason. Reason can be either of the atoms in the following list. The function error_description/1 returns a descriptive string that describes the error.

GPS devices usually communicate via serial interfaces. The most common type these days are USB GPS devices, which have a serial converter behind USB. If you want to use one of these devices for PPS then please be aware that the majority do not signal PPS via USB. Check the GPSD hardware list for details. The examples below were run with a Navisys GR701-W.

To examine a list of the currently outstanding locks in a database server, use the pg_locks system view. For more information on monitoring the status of the lock manager subsystem, refer to Chapter 28. 2ff7e9595c