pg2(3erl) [linux man page]
pg2(3erl) Erlang Module Definition pg2(3erl) NAME
pg2 - Distributed Named Process Groups DESCRIPTION
This module implements process groups. The groups in this module differ from the groups in the module pg in several ways. In pg , each mes- sage is sent to all members in the group. In this module, each message may be sent to one, some, or all members. A group of processes can be accessed by a common name. For example, if there is a group named foobar , there can be a set of processes (which can be located on different nodes) which are all members of the group foobar . There are no special functions for sending a message to the group. Instead, client functions should be written with the functions get_members/1 and get_local_members/1 to find out which pro- cesses are members of the group. Then the message can be sent to one or more members of the group. If a member terminates, it is automatically removed from the group. Warning: This module is used by the disk_log module for managing distributed disk logs. The disk log names are used as group names, which means that some action may need to be taken to avoid name clashes. EXPORTS
create(Name) -> void() Types Name = term() Creates a new, empty process group. The group is globally visible on all nodes. If the group exists, nothing happens. delete(Name) -> void() Types Name = term() Deletes a process group. get_closest_pid(Name) -> Pid | {error, Reason} Types Name = term() Pid = pid() Reason = {no_process, Name} | {no_such_group, Name} This is a useful dispatch function which can be used from client functions. It returns a process on the local node, if such a process exist. Otherwise, it chooses one randomly. get_members(Name) -> [Pid] | {error, Reason} Types Name = term() Pid = pid() Reason = {no_such_group, Name} Returns all processes in the group Name . This function should be used from within a client function that accesses the group. It is therefore optimized for speed. get_local_members(Name) -> [Pid] | {error, Reason} Types Name = term() Pid = pid() Reason = {no_such_group, Name} Returns all processes running on the local node in the group Name . This function should to be used from within a client function that accesses the group. It is therefore optimized for speed. join(Name, Pid) -> ok | {error, Reason} Types Name = term() Pid = pid() Reason = {no_such_group, Name} Joins the process Pid to the group Name . A process can join a group several times; it must then leave the group the same number of times. leave(Name, Pid) -> ok | {error, Reason} Types Name = term() Pid = pid() Reason = {no_such_group, Name} Makes the process Pid leave the group Name . If the process is not a member of the group, ok is returned. which_groups() -> [Name] Types Name = term() Returns a list of all known groups. start() start_link() -> {ok, Pid} | {error, Reason} Types Pid = pid() Reason = term() Starts the pg2 server. Normally, the server does not need to be started explicitly, as it is started dynamically if it is needed. This is useful during development, but in a target system the server should be started explicitly. Use configuration parameters for kernel for this. SEE ALSO
kernel(7) , pg(3erl) Ericsson AB kernel 2.14.3 pg2(3erl)
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timer(3erl) Erlang Module Definition timer(3erl) NAME
timer - Timer Functions DESCRIPTION
This module provides useful functions related to time. Unless otherwise stated, time is always measured in milliseconds . All timer func- tions return immediately, regardless of work carried out by another process. Successful evaluations of the timer functions yield return values containing a timer reference, denoted TRef below. By using cancel/1 , the returned reference can be used to cancel any requested action. A TRef is an Erlang term, the contents of which must not be altered. The timeouts are not exact, but should be at least as long as requested. EXPORTS
start() -> ok Starts the timer server. Normally, the server does not need to be started explicitly. It is started dynamically if it is needed. This is useful during development, but in a target system the server should be started explicitly. Use configuration parameters for kernel for this. apply_after(Time, Module, Function, Arguments) -> {ok, Tref} | {error, Reason} Types Time = integer() in Milliseconds Module = Function = atom() Arguments = [term()] Evaluates apply(M, F, A) after Time amount of time has elapsed. Returns {ok, TRef} , or {error, Reason} . send_after(Time, Pid, Message) -> {ok, TRef} | {error,Reason} send_after(Time, Message) -> {ok, TRef} | {error,Reason} Types Time = integer() in Milliseconds Pid = pid() | atom() Message = term() Result = {ok, TRef} | {error, Reason} send_after/3 : Evaluates Pid ! Message after Time amount of time has elapsed. ( Pid can also be an atom of a registered name.) Returns {ok, TRef} , or {error, Reason} . send_after/2 : Same as send_after(Time, self(), Message) . exit_after(Time, Pid, Reason1) -> {ok, TRef} | {error,Reason2} exit_after(Time, Reason1) -> {ok, TRef} | {error,Reason2} kill_after(Time, Pid)-> {ok, TRef} | {error,Reason2} kill_after(Time) -> {ok, TRef} | {error,Reason2} Types Time = integer() in milliseconds Pid = pid() | atom() Reason1 = Reason2 = term() exit_after/3 : Send an exit signal with reason Reason1 to Pid Pid . Returns {ok, TRef} , or {error, Reason2} . exit_after/2 : Same as exit_after(Time, self(), Reason1) . kill_after/2 : Same as exit_after(Time, Pid, kill) . kill_after/1 : Same as exit_after(Time, self(), kill) . apply_interval(Time, Module, Function, Arguments) -> {ok, TRef} | {error, Reason} Types Time = integer() in milliseconds Module = Function = atom() Arguments = [term()] Evaluates apply(Module, Function, Arguments) repeatedly at intervals of Time . Returns {ok, TRef} , or {error, Reason} . send_interval(Time, Pid, Message) -> {ok, TRef} | {error, Reason} send_interval(Time, Message) -> {ok, TRef} | {error, Reason} Types Time = integer() in milliseconds Pid = pid() | atom() Message = term() Reason = term() send_interval/3 : Evaluates Pid ! Message repeatedly after Time amount of time has elapsed. ( Pid can also be an atom of a registered name.) Returns {ok, TRef} or {error, Reason} . send_interval/2 : Same as send_interval(Time, self(), Message) . cancel(TRef) -> {ok, cancel} | {error, Reason} Cancels a previously requested timeout. TRef is a unique timer reference returned by the timer function in question. Returns {ok, cancel} , or {error, Reason} when TRef is not a timer reference. sleep(Time) -> ok Types Time = integer() in milliseconds or the atom infinity Suspends the process calling this function for Time amount of milliseconds and then returns ok , or suspend the process forever if Time is the atom infinity . Naturally, this function does not return immediately. tc(Module, Function, Arguments) -> {Time, Value} tc(Fun, Arguments) -> {Time, Value} Types Module = Function = atom() Fun = fun() Arguments = [term()] Time = integer() in microseconds Value = term() tc/3 : Evaluates apply(Module, Function, Arguments) and measures the elapsed real time as reported by now/0 . Returns {Time, Value} , where Time is the elapsed real time in microseconds , and Value is what is returned from the apply. tc/2 : Evaluates apply(Fun, Arguments) . Otherwise works like tc/3 . now_diff(T2, T1) -> Tdiff Types T1 = T2 = {MegaSecs, Secs, MicroSecs} Tdiff = MegaSecs = Secs = MicroSecs = integer() Calculates the time difference Tdiff = T2 - T1 in microseconds , where T1 and T2 probably are timestamp tuples returned from erlang:now/0 . seconds(Seconds) -> Milliseconds Returns the number of milliseconds in Seconds . minutes(Minutes) -> Milliseconds Return the number of milliseconds in Minutes . hours(Hours) -> Milliseconds Returns the number of milliseconds in Hours . hms(Hours, Minutes, Seconds) -> Milliseconds Returns the number of milliseconds in Hours + Minutes + Seconds . EXAMPLES
This example illustrates how to print out "Hello World!" in 5 seconds: 1> timer:apply_after(5000, io, format, ["~nHello World!~n", []]). {ok,TRef} Hello World! The following coding example illustrates a process which performs a certain action and if this action is not completed within a certain limit, then the process is killed. Pid = spawn(mod, fun, [foo, bar]), %% If pid is not finished in 10 seconds, kill him {ok, R} = timer:kill_after(timer:seconds(10), Pid), ... %% We change our mind... timer:cancel(R), ... WARNING
A timer can always be removed by calling cancel/1 . An interval timer, i.e. a timer created by evaluating any of the functions apply_interval/4 , send_interval/3 , and send_interval/2 , is linked to the process towards which the timer performs its task. A one-shot timer, i.e. a timer created by evaluating any of the functions apply_after/4 , send_after/3 , send_after/2 , exit_after/3 , exit_after/2 , kill_after/2 , and kill_after/1 is not linked to any process. Hence, such a timer is removed only when it reaches its time- out, or if it is explicitly removed by a call to cancel/1 . Ericsson AB stdlib 1.17.3 timer(3erl)