From 3d70cee4034e4da37d125679345aa2a10c58cb34 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Tue, 14 Apr 2015 23:21:36 +0200 Subject: Update Kernel documentation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Language cleaned up by technical writers from Combitech. Proofreading and corrections by Björn Gustavsson and Hans Bolinder. --- lib/kernel/doc/src/global.xml | 296 ++++++++++++++++++++---------------------- 1 file changed, 138 insertions(+), 158 deletions(-) (limited to 'lib/kernel/doc/src/global.xml') diff --git a/lib/kernel/doc/src/global.xml b/lib/kernel/doc/src/global.xml index bd75945115..4442741f54 100644 --- a/lib/kernel/doc/src/global.xml +++ b/lib/kernel/doc/src/global.xml @@ -4,7 +4,7 @@
- 19962013 + 19962016 Ericsson AB. All Rights Reserved. @@ -29,82 +29,67 @@
global - A Global Name Registration Facility + A global name registration facility. -

This documentation describes the Global module which consists - of the following functionalities:

- +

This module consists of the following services:

- registration of global names; - global locks; - maintenance of the fully connected network. + Registration of global names + Global locks + Maintenance of the fully connected network - -

These services are controlled via the process - global_name_server which exists on every node. The global - name server is started automatically when a node is started. +

These services are controlled through the process + global_name_server that exists on every node. The global + name server starts automatically when a node is started. With the term global is meant over a system consisting - of several Erlang nodes.

- + of many Erlang nodes.

The ability to globally register names is a central concept in the programming of distributed Erlang systems. In this module, the equivalent of the register/2 and whereis/1 - BIFs (for local name registration) are implemented, but for a + BIFs (for local name registration) are provided, but for a network of Erlang nodes. A registered name is an alias for a process identifier (pid). The global name server monitors - globally registered pids. If a process terminates, the name will - also be globally unregistered.

- + globally registered pids. If a process terminates, the name is + also globally unregistered.

The registered names are stored in replica global name tables on every node. There is no central storage point. Thus, the translation of a name to a pid is fast, as it is always done - locally. When any action in taken which results in a change to - the global name table, all tables on other nodes are automatically - updated.

- + locally. For any action resulting in a change to the global name table, + all tables on other nodes are automatically updated.

Global locks have lock identities and are set on a specific - resource. For instance, the specified resource could be a pid. + resource. For example, the specified resource can be a pid. When a global lock is set, access to the locked resource is - denied for all other resources other than the lock requester.

- -

Both the registration and lock functionalities are atomic. All - nodes involved in these actions will have the same view of + denied for all resources other than the lock requester.

+

Both the registration and lock services are atomic. + All nodes involved in these actions have the same view of the information.

-

The global name server also performs the critical task of - continuously monitoring changes in node configuration: if a node - which runs a globally registered process goes down, the name - will be globally unregistered. To this end the global name + continuously monitoring changes in node configuration. If a node + that runs a globally registered process goes down, the name + is globally unregistered. To this end, the global name server subscribes to nodeup and nodedown messages - sent from the net_kernel module. Relevant Kernel + sent from module net_kernel. Relevant Kernel application variables in this context are net_setuptime, net_ticktime, and dist_auto_connect. See also - kernel(6).

- -

The name server will also maintain a fully connected network. For + kernel(6).

+

The name server also maintains a fully connected network. For example, if node N1 connects to node N2 (which is already connected to N3), the global name servers on the - nodes N1 and N3 will make sure that also N1 - and N3 are connected. If this is not desired, the command - line flag -connect_all false can be used (see also - erl(1)). In - this case the name registration facility cannot be used, but the - lock mechanism will still work.

- + nodes N1 and N3 ensure that also N1 + and N3 are connected. If this is not desired, + command-line flag -connect_all false can be used (see also + erl(1)). + In this case, the name registration service cannot be used, but the + lock mechanism still works.

If the global name server fails to connect nodes (N1 and - N3 in the example above) a warning event is sent to the + N3 in the example), a warning event is sent to the error logger. The presence of such an event does not exclude the - possibility that the nodes will later connect--one can for - example try the command rpc:call(N1, net_adm, ping, [N2]) in - the Erlang shell--but it indicates some kind of problem with - the network.

- + nodes to connect later (you can, for + example, try command rpc:call(N1, net_adm, ping, [N2]) in + the Erlang shell), but it indicates a network problem.

-

If the fully connected network is not set up properly, the - first thing to try is to increase the value of - net_setuptime.

+

If the fully connected network is not set up properly, try + first to increase the value of net_setuptime.

 - @@ -117,7 +102,7 @@ - Delete a lock + Delete a lock.

Deletes the lock Id synchronously.

 @@ -125,11 +110,13 @@ - Name resolving function that notifies both pids + Name resolving function that notifies both pids. -

This function can be used as a name resolving function for - register_name/3 and re_register_name/3. It - unregisters both pids, and sends the message +

Can be used as a name resolving function for + register_name/3 + and + re_register_name/3.

+

The function unregisters both pids and sends the message {global_name_conflict, Name, OtherPid} to both processes.

 @@ -137,85 +124,97 @@ - Name resolving function that kills one pid + Name resolving function that kills one pid. -

This function can be used as a name resolving function for - register_name/3 and re_register_name/3. It - randomly chooses one of the pids for registration and kills - the other one.

+

Can be used as a name resolving function for + register_name/3 + and + re_register_name/3.

+

The function randomly selects one of the pids for registration and + kills the other one.

 - Name resolving function that notifies one pid + Name resolving function that notifies one pid. -

This function can be used as a name resolving function for - register_name/3 and re_register_name/3. It - randomly chooses one of the pids for registration, and sends - the message {global_name_conflict, Name} to the other - pid.

+

Can be used as a name resolving function for + register_name/3 + and + re_register_name/3.

+

The function randomly selects one of the pids for registration, and + sends the message {global_name_conflict, Name} to + the other pid.

+ + + + + + + Atomically re-register a name. + + {Module, Function} + is also allowed. + + +

Atomically changes the registered name Name on + all nodes to refer to Pid.

+

Function Resolve has the same behavior as in + register_name/2,3. +

- Globally register a name for a pid + Globally register a name for a pid. - {Module, Function} - is currently also allowed for backward compatibility, but its use is - deprecated + {Module, Function} is also + allowed for backward compatibility, but its use is deprecated. -

Globally associates the name Name with a pid, that is, - Globally notifies all nodes of a new global name in a network +

Globally associates name Name with a pid, that + is, globally notifies all nodes of a new global name in a network of Erlang nodes.

-

When new nodes are added to the network, they are informed of the globally registered names that already exist. The network is also informed of any global names in newly connected nodes. If any name clashes are discovered, - the Resolve function is called. Its purpose is to + function Resolve is called. Its purpose is to decide which pid is correct. If the function crashes, or returns anything other than one of the pids, the name is unregistered. This function is called once for each name clash.

-

If you plan to change code without restarting your system, you must use an external fun (fun Module:Function/Arity) - as the Resolve function; if you use a - local fun you can never replace the code for the module that - the fun belongs to. -

+ as function Resolve. If you use a + local fun, you can never replace the code for the module that + the fun belongs to.

 - -

There are three pre-defined resolve functions: +

Three predefined resolve functions exist: random_exit_name/3, random_notify_name/3, and - notify_all_name/3. If no Resolve function is - defined, random_exit_name is used. This means that one - of the two registered processes will be selected as correct + notify_all_name/3. If no Resolve function + is defined, random_exit_name is used. This means that one + of the two registered processes is selected as correct while the other is killed.

- -

This function is completely synchronous. This means that +

This function is completely synchronous, that is, when this function returns, the name is either registered on all nodes or none.

-

The function returns yes if successful, no if it fails. For example, no is returned if an attempt is made to register an already registered process or to register a process with a name that is already in use.

- -

Releases up to and including OTP R10 did not check if the - process was already registered. As a consequence the - global name table could become inconsistent. The old +

Releases up to and including Erlang/OTP R10 did not check if the + process was already registered. The global name table could + therefore become inconsistent. The old (buggy) behavior can be chosen by giving the Kernel application variable global_multi_name_action the value allow.

 -

If a process with a registered name dies, or the node goes down, the name is unregistered on all nodes.

 @@ -223,38 +222,20 @@ - All globally registered names - -

Returns a lists of all globally registered names.

- - - - - - - Atomically re-register a name - - {Module, Function} - is also allowed - + All globally registered names. -

Atomically changes the registered name Name on all - nodes to refer to Pid.

- -

The Resolve function has the same behavior as in - register_name/2,3.

+

Returns a list of all globally registered names.

 - Send a message to a globally registered pid + Send a message to a globally registered pid. -

Sends the message Msg to the pid globally registered +

Sends message Msg to the pid globally registered as Name.

- -

Failure: If Name is not a globally registered - name, the calling function will exit with reason +

If Name is not a globally registered + name, the calling function exits with reason {badarg, {Name, Msg}}.

 @@ -263,7 +244,7 @@ - Set a lock on the specified nodes + Set a lock on the specified nodes. @@ -271,50 +252,48 @@ are specified) on ResourceId for LockRequesterId. If a lock already exists on ResourceId for another requester than - LockRequesterId, and Retries is not equal to 0, - the process sleeps for a while and will try to execute - the action later. When Retries attempts have been made, - false is returned, otherwise true. If - Retries is infinity, true is eventually - returned (unless the lock is never released).

- -

If no value for Retries is given, infinity is - used.

- + LockRequesterId, and Retries + is not equal to 0, the process sleeps for a while and tries + to execute the action later. When Retries + attempts have been made, false is returned, otherwise + true. If Retries is infinity, + true is eventually returned (unless the lock is never + released).

+

If no value for Retries is specified, + infinity is used.

This function is completely synchronous.

- -

If a process which holds a lock dies, or the node goes +

If a process that holds a lock dies, or the node goes down, the locks held by the process are deleted.

-

The global name server keeps track of all processes sharing the same lock, that is, if two processes set the same lock, both processes must delete the lock.

-

This function does not address the problem of a deadlock. A deadlock can never occur as long as processes only lock one - resource at a time. But if some processes try to lock two or - more resources, a deadlock may occur. It is up to the + resource at a time. A deadlock can occur if some processes + try to lock two or more resources. It is up to the application to detect and rectify a deadlock.

- -

Some values of ResourceId should be avoided or - Erlang/OTP will not work properly. A list of resources to - avoid: global, dist_ac, - mnesia_table_lock, mnesia_adjust_log_writes, - pg2.

+

Avoid the following values of ResourceId, + otherwise Erlang/OTP does not work properly:

+ + dist_ac + global + mnesia_adjust_log_writes + mnesia_table_lock + pg2 + - - Synchronize the global name server + Synchronize the global name server.

Synchronizes the global name server with all nodes known to - this node. These are the nodes which are returned from + this node. These are the nodes that are returned from erlang:nodes(). When this function returns, - the global name server will receive global information from + the global name server receives global information from all nodes. This function can be called when new nodes are added to the network.

The only possible error reason Reason is @@ -326,24 +305,25 @@ - Micro transaction facility + Micro transaction facility. -

Sets a lock on Id (using set_lock/3). If this - succeeds, Fun() is evaluated and the result Res - is returned. Returns aborted if the lock attempt - failed. If Retries is set to infinity, - the transaction will not abort.

- -

infinity is the default setting and will be used if - no value is given for Retries.

+

Sets a lock on Id (using + set_lock/3). + If this succeeds, Fun() is evaluated and the + result Res + is returned. Returns aborted if the lock attempt fails. + If Retries is set to infinity, + the transaction does not abort.

+

infinity is the default setting and is used if + no value is specified for Retries.

 - Remove a globally registered name for a pid + Remove a globally registered name for a pid.

Removes the globally registered name Name from the network of Erlang nodes.

@@ -352,7 +332,7 @@ - Get the pid with a given globally registered name + Get the pid with a specified globally registered name.

Returns the pid with the globally registered name Name. Returns undefined if the name is not @@ -363,8 +343,8 @@

See Also -

global_group(3), - net_kernel(3)

+

global_group(3), + net_kernel(3)

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