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SunOS 5.10 - man page for attributes (sunos section 5)

attributes(5)						Standards, Environments, and Macros					     attributes(5)

NAME
attributes, architecture, availability, CSI, stability, MT-Level - attributes of interfaces
DESCRIPTION
The ATTRIBUTES section of a manual page contains a table (see below) defining attribute types and their corresponding values. +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Architecture |SPARC | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ |CSI |Enabled | +-----------------------------+-----------------------------+ |Interface Stability |Unstable | +-----------------------------+-----------------------------+ |MT-Level |Safe | +-----------------------------+-----------------------------+ Architecture Architecture defines processor or specific hardware. See -p option of uname(1). In some cases, it may indicate required adapters or periph- erals. Availability This refers to the software package which contains the command or component being described on the man page. To be able to use the com- mand, the indicated package must have been installed. For information on how to add a package see pkgadd(1M). Code Set Independence (CSI) OS utilities and libraries which are free of dependencies on the properties of any code sets are said to have Code Set Independence (CSI). They have the attribute of being CSI enabled. This is in contrast to many commands and utilities, for example, that work only with Extended Unix Codesets (EUC), an encoding method that allows concurrent support for up to four code sets and is commonly used to represent Asian character sets. However, for practical reasons, this independence is not absolute. Certain assumptions are still applied to the current CSI implementation: o File code is a superset of ASCII. o To support multi-byte characters and null-terminated UNIX file names, the NULL and / (slash) characters cannot be part of any multi- byte characters. o Only "stateless" file code encodings are supported. Stateless encoding avoids shift, locking shift, designation, invocation, and so forth, although single shift is not excluded. o Process code (wchar_t values) is implementation dependent and can change over time or between implementations or between locales. o Not every object can have names composed of arbitrary characters. The names of the following objects must be composed of ASCII charac- ters: o User names, group name, and passwords o System name o Names of printers and special devices o Names of terminals (/dev/tty*) o Process ID numbers o Message queues, semaphores, and shared memory labels. o The following may be composed of ISO Latin-1 or EUC characters: o File names o Directory names o Command names o Shell variables and environmental variable names o Mount points for file systems o NIS key names and domain names o The names of NFS shared files should be composed of ASCII characters. Although files and directories may have names and contents com- posed of characters from non-ASCII code sets, using only the ASCII codeset allows NFS mounting across any machine, regardless of localization. For the commands and utilities that are CSI enabled, all can handle single-byte and multi-byte locales released in 2.6. For applications to get full support of internationalization services, dynamic binding has to be applied. Statically bound programs will only get support for C and POSIX locales. Interface Stability Sun often provides developers with early access to new technologies, which allows developers to evaluate with them as soon as possible. Unfortunately, new technologies are prone to changes and standardization often results in interface incompatibility from previous versions. To make reasonable risk assessments, developers need to know how likely an interface is to change in future releases. To aid developers in making these assessments, interface stability information is included on some manual pages for commands, entry-points, and file formats. The more stable interfaces can safely be used by nearly all applications, because Sun will endeavor to ensure that these continue to work in future minor releases. Applications that depend only on Standard and Stable interfaces should reliably continue to function correctly on future minor releases (but not necessarily on earlier major releases). The less stable interfaces allow experimentation and prototyping, but should be used only with the understanding that they might change incompatibly or even be dropped or replaced with alternatives in future minor releases. "Interfaces" that Sun does not document (for example, most kernel data structures and some symbols in system header files) may be implemen- tation artifacts. Such internal interfaces are not only subject to incompatible change or removal, but we are unlikely to mention such a change in release notes. Release Levels Products are given release levels, as well as names, to aid compatibility discussions. Each release level may also include changes suitable for lower levels. Release Version Significance Major x.0 Likely to contain major feature additions; adhere to different, possibly incompat- ible Standard revisions; and though unlikely, could change, drop, or replace Standard or Stable interfaces. Ini- tial product releases are usu- ally 1.0. Minor x.y Compared to an x.0 or earlier release (y!=0), it's likely to contain: minor feature additions, compat- ible Standard and Stable interfaces, possibly incompat- ible Evolving interfaces, or likely incompati- ble Unstable interfaces. Micro x.y.z Intended to be interface compati- ble with the pre- vious release (z!=0), but likely to add bug fixes, performance enhancements, and support for addi- tional hardware. Classifications The following table summarizes how stability level classifications relate to release level. The first column lists the Stability Level. The second column lists the Release Level for Incompatable Changes, and the third column lists other comments. For a complete discussion of individual classifications, see the appropriate subsection below. Stability Release Comments Standard Major (x.0) Actual or de facto. Stable Major (x.0) Incompatibilities are exceptional. Evolving Minor (x.y) Migration advice might accompany an incompatibility. Unstable Minor (x.y) Experimental or transitional: incompatibilities are common. External Micro (x.y.z) Not controlled by Sun: intrarelease incompatibilities are common. Obsolete Minor (x.y) Deprecated interface: likely to be removed in a future minor release. The interface stability level classifications described on this manual page apply to both source and binary interfaces unless otherwise stated. All stability level classifications are public, with the exception of the Private classification. The stability level of a docu- mented interface (one that is documented in the manual pages) is unspecified unless explicitly stated. The stability level of an undocu- mented interface is implicitly Private. The existence of documentation other than the documentation that is a component of the Solaris product should not be construed to imply any level of stability for interfaces provided by the Solaris product. The only source of stability level information is Solaris manual pages. Standard[: [organization_name,] standard_name, version] The documented interface complies with the standard listed. If a standard is not specified the interface is defined by several stan- dards. This is usually the hierarchy built up from the C Language (defined by ISO/IEC or K&R), SVID 3 and associated ABIs (defined by AT&T), the POSIX standards (defined by IEEE and ISO/IEC), and the Single UNIX Specifications (defined by The Open Group). See stan- dards(5) for a complete list of these standards. Most of these interfaces are defined by a formal standard, and controlled by a standards development organization. Changes will usually be made in accordance with approved changes to that standard. This stability level can also apply to interfaces that have been adopted (without a formal standard) by an "industry convention." Support is provided for only the specified version(s) of a standard; support for later versions is not guaranteed. If the standards development organization approves a non-upward-compatible change to a Standard interface that Sun decides to support, Sun will announce a compatibility and migration strategy. Programmers producing portable applications should rely on the interface descriptions present in the standard or specification to which the application is intended to conform, rather than the manual page descriptions of Standard interfaces. When the standard or specifi- cation allows alternative implementation choices, the manual page usually only describes the alternative implemented by Sun. The manual page also describes any compatible extensions to the base definition of Standard interfaces provided by Sun. Stable A Stable interface is a mature interface under Sun's control. Sun will try to avoid non-upwards-compatible changes to these interfaces, especially in minor or micro releases. If support of a Stable interface must be discontinued, Sun will attempt to provide notification and the stability level changes to Obsolete. Evolving An Evolving interface may eventually become Standard or Stable but is still in transition. Sun will make reasonable efforts to ensure compatibility with previous releases as it evolves. When non-upwards compatible changes become necessary, they will occur in minor and major releases; such changes will be avoided in micro releases whenever possible. If such a change is necessary, it will be documented in the release notes for the affected release, and when feasible, Sun will provide migration aids for binary compatibility and continued source development. External An External interface is controlled by an entity other than Sun. At Sun's discretion, Sun can deliver as part of any release updated and possibly incompatible versions of such interfaces, subject to their availability from the controlling entity. This classification is typically applied to publicly available "freeware" and similar objects. For External interfaces, Sun makes no claims regarding either source or binary compatibility between any two releases. Applications based on these interfaces might not work in future releases, including patches that contain External interfaces. Unstable An Unstable interface is provided to give developers early access to new or rapidly changing technology or as an interim solution to a problem for which a more stable solution is anticipated in the future. For Unstable interfaces, Sun makes no claims about either source or binary compatibility from one minor release to another. Applica- tions developed based on these interfaces may not work in future minor releases. Obsolete: Scheduled for removal after event An Obsolete interface is supported in the current release, but is scheduled to be removed in a future (minor) release. When support of an interface is to be discontinued, Sun will attempt to provide notification before discontinuing support. Use of an Obsolete interface may produce warning messages. Private A Private interface is an interface provided by a component (or product) intended only for the use of that component. A Private inter- face might still be visible to or accessible by other components. Because the use of interfaces private to another component carries great stability risks, such use is explicitly not supported. Components not supplied by Sun Microsystems should not use Private inter- faces. Most Private interfaces are not documented. It is an exceptional case when a Private interface is documented. Reasons for documenting a Private interface include, but are not limited to, the intention that the interface might be reclassified to one of the public stabil- ity level classifications in the future or the fact that the interface is inordinately visible. MT-Level Libraries are classified into categories that define their ability to support multiple threads. Manual pages containing functions that are of multiple or differing levels describe this in their NOTES or USAGE section. Safe Safe is an attribute of code that can be called from a multithreaded application. The effect of calling into a Safe interface or a safe code segment is that the results are valid even when called by multiple threads. Often overlooked is the fact that the result of this Safe interface or safe code segment can have global consequences that affect all threads. For example, the action of opening or closing a file from one thread is visible by all the threads within a process. A multithreaded application has the responsibility for using these interfaces in a safe manner, which is different from whether or not the interface is Safe. For example, a multithreaded applica- tion that closes a file that is still in use by other threads within the application is not using the close(2) interface safely. Unsafe An Unsafe library contains global and static data that is not protected. It is not safe to use unless the application arranges for only one thread at time to execute within the library. Unsafe libraries might contain functions that are Safe; however, most of the library's functions are unsafe to call. Some functions that are Unsafe have reentrant counterparts that are MT-Safe. Reentrant func- tions are designated by the _r suffix appended to the function name. MT-Safe An MT-Safe library is fully prepared for multithreaded access. It protects its global and static data with locks, and can provide a reasonable amount of concurrency. A library can be safe to use, but not MT-Safe. For example, surrounding an entire library with a mon- itor makes the library Safe, but it supports no concurrency so it is not considered MT-Safe. An MT-Safe library must permit a reason- able amount of concurrency. (This definition's purpose is to give precision to what is meant when a library is described as Safe. The definition of a Safe library does not specify if the library supports concurrency. The MT-Safe definition makes it clear that the library is Safe, and supports some concurrency. This clarifies the Safe definition, which can mean anything from being single threaded to being any degree of multithreaded.) Async-Signal-Safe Async-Signal-Safe refers to particular library functions that can be safely called from a signal handler. A thread that is executing an Async-Signal-Safe function will not deadlock with itself if interrupted by a signal. Signals are only a problem for MT-Safe functions that acquire locks. Async-Signal-Safe functions are also MT-Safe. Signals are disabled when locks are acquired in Async-Signal-Safe functions. These sig- nals prevent a signal handler that might acquire the same lock from being called. MT-Safe with Exceptions See the NOTES or USAGE sections of these pages for a description of the exceptions. Safe with Exceptions See the NOTES or USAGE sections of these pages for a description of the exceptions. Fork-Safe The fork(2) function replicates only the calling thread in the child process. The fork1(2) function exists for compatibility with the past and is synonymous with fork(). If a thread other than the one performing the fork holds a lock when fork() is called, the lock will still be held in the child process but there will be no lock owner since the owning thread was not replicated. A child calling a function that attempts to acquire the lock will deadlock itself. When fork() is called, a Fork-Safe library arranges to have all of its internal locks held only by the thread performing the fork. This is usually accomplished with pthread_atfork(3C), which is called when the library is initialized. The forkall(2) function provides the capability for the rare case when a process needs to replicate all of its threads when performing a fork. No pthread_atfork() actions are performed when forkall() is called. There are dangers associated with calling forkall(). If some threads in a process are performing I/O operations when another thread calls forkall(), they will continue performing the same I/O operations in both the parent and child processes, possibly causing data corruption. For this and other race-condition reasons, the use of forkall() is discouraged. In all Solaris releases prior to Solaris 10, the behavior of fork() depended on whether or not the application was linked with -lpthread (POSIX threads, see standards(5)). If linked with -lpthread, fork() behaved like fork1(); otherwise it behaved like forkall(). To avoid any confusion concerning the behavior of fork(), applications can specifically call fork1() or forkall() as appro- priate. Cancel-Safety If a multithreaded application uses pthread_cancel(3C) to cancel (that is, kill) a thread, it is possible that the target thread is killed while holding a resource, such as a lock or allocated memory. If the thread has not installed the appropriate cancellation cleanup handlers to release the resources appropriately (see pthread_cancel(3C)), the application is "cancel-unsafe", that is, it is not safe with respect to cancellation. This unsafety could result in deadlocks due to locks not released by a thread that gets can- celled, or resource leaks; for example, memory not being freed on thread cancellation. All applications that use pthread_cancel(3C) should ensure that they operate in a Cancel-Safe environment. Libraries that have cancellation points and which acquire resources such as locks or allocate memory dynamically, also contribute to the cancel-unsafety of applications that are linked with these libraries. This introduces another level of safety for libraries in a multithreaded program: Cancel-Safety. There are two sub-categories of Can- cel-Safety: Deferred-Cancel-Safety, and Asynchronous-Cancel-Safety. An application is considered to be Deferred-Cancel-Safe when it is Cancel-Safe for threads whose cancellation type is PTHREAD_CANCEL_DEFERRED. An application is considered to be Asynchronous-Cancel-Safe when it is Cancel-Safe for threads whose cancellation type is PTHREAD_CANCEL_ASYNCHRONOUS. Deferred-Cancel-Safety is easier to achieve than Asynchronous-Cancel-Safety, since a thread with the deferred cancellation type can be cancelled only at well-defined cancellation points, whereas a thread with the asynchronous cancellation type can be cancelled anywhere. Since all threads are created by default to have the deferred cancellation type, it might never be necessary to worry about asynchronous cancel safety. Most applications and libraries are expected to always be Asynchronous-Cancel-Unsafe. An application which is Asynchronous-Cancel-Safe is also, by defini- tion, Deferred-Cancel-Safe.
SEE ALSO
uname(1), pkgadd(1M), Intro(3), standards(5) SunOS 5.10 19 Dec 2003 attributes(5)

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