1IO::Async::Function(3)User Contributed Perl DocumentationIO::Async::Function(3)
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NAME

6       "IO::Async::Function" - call a function asynchronously
7

SYNOPSIS

9          use IO::Async::Function;
10
11          use IO::Async::Loop;
12          my $loop = IO::Async::Loop->new;
13
14          my $function = IO::Async::Function->new(
15             code => sub {
16                my ( $number ) = @_;
17                return is_prime( $number );
18             },
19          );
20
21          $loop->add( $function );
22
23          $function->call(
24             args => [ 123454321 ],
25          )->on_done( sub {
26             my $isprime = shift;
27             print "123454321 " . ( $isprime ? "is" : "is not" ) . " a prime number\n";
28          })->on_fail( sub {
29             print STDERR "Cannot determine if it's prime - $_[0]\n";
30          })->get;
31

DESCRIPTION

33       This subclass of IO::Async::Notifier wraps a function body in a
34       collection of worker processes, to allow it to execute independently of
35       the main process.  The object acts as a proxy to the function, allowing
36       invocations to be made by passing in arguments, and invoking a
37       continuation in the main process when the function returns.
38
39       The object represents the function code itself, rather than one
40       specific invocation of it. It can be called multiple times, by the
41       "call" method.  Multiple outstanding invocations can be called; they
42       will be dispatched in the order they were queued. If only one worker
43       process is used then results will be returned in the order they were
44       called. If multiple are used, then each request will be sent in the
45       order called, but timing differences between each worker may mean
46       results are returned in a different order.
47
48       Since the code block will be called multiple times within the same
49       child process, it must take care not to modify any of its state that
50       might affect subsequent calls. Since it executes in a child process, it
51       cannot make any modifications to the state of the parent program.
52       Therefore, all the data required to perform its task must be
53       represented in the call arguments, and all of the result must be
54       represented in the return values.
55
56       The Function object is implemented using an IO::Async::Routine with two
57       IO::Async::Channel objects to pass calls into and results out from it.
58
59       The IO::Async framework generally provides mechanisms for multiplexing
60       IO tasks between different handles, so there aren't many occasions when
61       such an asynchronous function is necessary. Two cases where this does
62       become useful are:
63
64       1.  When a large amount of computationally-intensive work needs to be
65           performed (for example, the "is_prime" test in the example in the
66           "SYNOPSIS").
67
68       2.  When a blocking OS syscall or library-level function needs to be
69           called, and no nonblocking or asynchronous version is supplied.
70           This is used by IO::Async::Resolver.
71
72       This object is ideal for representing "pure" functions; that is, blocks
73       of code which have no stateful effect on the process, and whose result
74       depends only on the arguments passed in. For a more general co-routine
75       ability, see also IO::Async::Routine.
76

PARAMETERS

78       The following named parameters may be passed to "new" or "configure":
79
80   code => CODE
81       The body of the function to execute.
82
83          @result = $code->( @args )
84
85   init_code => CODE
86       Optional. If defined, this is invoked exactly once in every child
87       process or thread, after it is created, but before the first invocation
88       of the function body itself.
89
90          $init_code->()
91
92   module => STRING
93   func => STRING
94       Since version 0.79.
95
96       An alternative to the "code" argument, which names a module to load and
97       a function to call within it. "module" should give a perl module name
98       (i.e.  "Some::Name", not a filename like Some/Name.pm), and "func"
99       should give the basename of a function within that module (i.e. without
100       the module name prefixed). It will be invoked, without extra arguments,
101       as the main code body of the object.
102
103       The task of loading this module and resolving the resulting function
104       from it is only performed on the remote worker side, so the controlling
105       process will not need to actually load the module.
106
107   init_func => STRING or ARRAY [ STRING, ... ]
108       Optional addition to the "module" and "func" alternatives. Names a
109       function within the module to call each time a new worker is created.
110
111       If this value is an array reference, its first element must be a string
112       giving the name of the function; the remaining values are passed to
113       that function as arguments.
114
115   model => "fork" | "thread" | "spawn"
116       Optional. Requests a specific IO::Async::Routine model. If not
117       supplied, leaves the default choice up to Routine.
118
119   min_workers => INT
120   max_workers => INT
121       The lower and upper bounds of worker processes to try to keep running.
122       The actual number running at any time will be kept somewhere between
123       these bounds according to load.
124
125   max_worker_calls => INT
126       Optional. If provided, stop a worker process after it has processed
127       this number of calls. (New workers may be started to replace stopped
128       ones, within the bounds given above).
129
130   idle_timeout => NUM
131       Optional. If provided, idle worker processes will be shut down after
132       this amount of time, if there are more than "min_workers" of them.
133
134   exit_on_die => BOOL
135       Optional boolean, controls what happens after the "code" throws an
136       exception. If missing or false, the worker will continue running to
137       process more requests. If true, the worker will be shut down. A new
138       worker might be constructed by the "call" method to replace it, if
139       necessary.
140
141   setup => ARRAY
142       Optional array reference. Specifies the "setup" key to pass to the
143       underlying IO::Async::Process when setting up new worker processes.
144

METHODS

146       The following methods documented with a trailing call to "->get" return
147       Future instances.
148
149   start
150          $function->start
151
152       Start the worker processes
153
154   stop
155          $function->stop
156
157       Stop the worker processes
158
159          $f = $function->stop
160
161       Since version 0.75.
162
163       If called in non-void context, returns a IO::Async::Future instance
164       that will complete once every worker process has stopped and exited.
165       This may be useful for waiting until all of the processes are waited
166       on, or other edge-cases, but is not otherwise particularly useful.
167
168   restart
169          $function->restart
170
171       Gracefully stop and restart all the worker processes.
172
173   call
174          @result = $function->call( %params )->get
175
176       Schedules an invocation of the contained function to be executed on one
177       of the worker processes. If a non-busy worker is available now, it will
178       be called immediately. If not, it will be queued and sent to the next
179       free worker that becomes available.
180
181       The request will already have been serialised by the marshaller, so it
182       will be safe to modify any referenced data structures in the arguments
183       after this call returns.
184
185       The %params hash takes the following keys:
186
187       args => ARRAY
188               A reference to the array of arguments to pass to the code.
189
190       priority => NUM
191               Optional. Defines the sorting order when no workers are
192               available and calls must be queued for later. A default of zero
193               will apply if not provided.
194
195               Higher values cause the call to be considered more important,
196               and will be placed earlier in the queue than calls with a
197               smaller value. Calls of equal priority are still handled in
198               FIFO order.
199
200       If the function body returns normally the list of results are provided
201       as the (successful) result of returned future. If the function throws
202       an exception this results in a failed future. In the special case that
203       the exception is in fact an unblessed "ARRAY" reference, this array is
204       unpacked and used as-is for the "fail" result. If the exception is not
205       such a reference, it is used as the first argument to "fail", in the
206       category of "error".
207
208          $f->done( @result )
209
210          $f->fail( @{ $exception } )
211          $f->fail( $exception, error => )
212
213   call (void)
214          $function->call( %params )
215
216       When not returning a future, the "on_result", "on_return" and
217       "on_error" arguments give continuations to handle successful results or
218       failure.
219
220       on_result => CODE
221               A continuation that is invoked when the code has been executed.
222               If the code returned normally, it is called as:
223
224                  $on_result->( 'return', @values )
225
226               If the code threw an exception, or some other error occurred
227               such as a closed connection or the process died, it is called
228               as:
229
230                  $on_result->( 'error', $exception_name )
231
232       on_return => CODE and on_error => CODE
233               An alternative to "on_result". Two continuations to use in
234               either of the circumstances given above. They will be called
235               directly, without the leading 'return' or 'error' value.
236
237   workers
238          $count = $function->workers
239
240       Returns the total number of worker processes available
241
242   workers_busy
243          $count = $function->workers_busy
244
245       Returns the number of worker processes that are currently busy
246
247   workers_idle
248          $count = $function->workers_idle
249
250       Returns the number of worker processes that are currently idle
251

EXAMPLES

253   Extended Error Information on Failure
254       The array-unpacking form of exception indiciation allows the function
255       body to more precicely control the resulting failure from the "call"
256       future.
257
258          my $divider = IO::Async::Function->new(
259             code => sub {
260                my ( $numerator, $divisor ) = @_;
261                $divisor == 0 and
262                   die [ "Cannot divide by zero", div_zero => $numerator, $divisor ];
263
264                return $numerator / $divisor;
265             }
266          );
267

NOTES

269       For the record, 123454321 is 11111 * 11111, a square number, and
270       therefore not prime.
271

AUTHOR

273       Paul Evans <leonerd@leonerd.org.uk>
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277perl v5.34.0                      2022-01-21            IO::Async::Function(3)
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