… | |
… | |
44 | about 20% smaller than the same data encoded as (compact) JSON or |
44 | about 20% smaller than the same data encoded as (compact) JSON or |
45 | Storable. |
45 | Storable. |
46 | |
46 | |
47 | In addition to the core CBOR data format, this module implements a |
47 | In addition to the core CBOR data format, this module implements a |
48 | number of extensions, to support cyclic and shared data structures (see |
48 | number of extensions, to support cyclic and shared data structures (see |
49 | "allow_sharing"), string deduplication (see "pack_strings") and scalar |
49 | "allow_sharing" and "allow_cycles"), string deduplication (see |
50 | references (always enabled). |
50 | "pack_strings") and scalar references (always enabled). |
51 | |
51 | |
52 | The primary goal of this module is to be *correct* and the secondary |
52 | The primary goal of this module is to be *correct* and the secondary |
53 | goal is to be *fast*. To reach the latter goal it was written in C. |
53 | goal is to be *fast*. To reach the latter goal it was written in C. |
54 | |
54 | |
55 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
55 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
… | |
… | |
141 | instead will emit a reference to the earlier value. |
141 | instead will emit a reference to the earlier value. |
142 | |
142 | |
143 | This means that such values will only be encoded once, and will not |
143 | This means that such values will only be encoded once, and will not |
144 | result in a deep cloning of the value on decode, in decoders |
144 | result in a deep cloning of the value on decode, in decoders |
145 | supporting the value sharing extension. This also makes it possible |
145 | supporting the value sharing extension. This also makes it possible |
146 | to encode cyclic data structures. |
146 | to encode cyclic data structures (which need "allow_cycles" to ne |
|
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147 | enabled to be decoded by this module). |
147 | |
148 | |
148 | It is recommended to leave it off unless you know your communication |
149 | It is recommended to leave it off unless you know your communication |
149 | partner supports the value sharing extensions to CBOR |
150 | partner supports the value sharing extensions to CBOR |
150 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
151 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
151 | support, the resulting data structure might be unusable. |
152 | support, the resulting data structure might be unusable. |
152 | |
153 | |
153 | Detecting shared values incurs a runtime overhead when values are |
154 | Detecting shared values incurs a runtime overhead when values are |
154 | encoded that have a reference counter large than one, and might |
155 | encoded that have a reference counter large than one, and might |
155 | unnecessarily increase the encoded size, as potentially shared |
156 | unnecessarily increase the encoded size, as potentially shared |
156 | values are encode as sharable whether or not they are actually |
157 | values are encode as shareable whether or not they are actually |
157 | shared. |
158 | shared. |
158 | |
159 | |
159 | At the moment, only targets of references can be shared (e.g. |
160 | At the moment, only targets of references can be shared (e.g. |
160 | scalars, arrays or hashes pointed to by a reference). Weirder |
161 | scalars, arrays or hashes pointed to by a reference). Weirder |
161 | constructs, such as an array with multiple "copies" of the *same* |
162 | constructs, such as an array with multiple "copies" of the *same* |
… | |
… | |
166 | data structures repeatedly, unsharing them in the process. Cyclic |
167 | data structures repeatedly, unsharing them in the process. Cyclic |
167 | data structures cannot be encoded in this mode. |
168 | data structures cannot be encoded in this mode. |
168 | |
169 | |
169 | This option does not affect "decode" in any way - shared values and |
170 | This option does not affect "decode" in any way - shared values and |
170 | references will always be decoded properly if present. |
171 | references will always be decoded properly if present. |
|
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172 | |
|
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173 | $cbor = $cbor->allow_cycles ([$enable]) |
|
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174 | $enabled = $cbor->get_allow_cycles |
|
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175 | If $enable is true (or missing), then "decode" will happily decode |
|
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176 | self-referential (cyclic) data structures. By default these will not |
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177 | be decoded, as they need manual cleanup to avoid memory leaks, so |
|
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178 | code that isn't prepared for this will not leak memory. |
|
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179 | |
|
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180 | If $enable is false (the default), then "decode" will throw an error |
|
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181 | when it encounters a self-referential/cyclic data structure. |
|
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182 | |
|
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183 | FUTURE DIRECTION: the motivation behind this option is to avoid |
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184 | *real* cycles - future versions of this module might chose to decode |
|
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185 | cyclic data structures using weak references when this option is |
|
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186 | off, instead of throwing an error. |
|
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187 | |
|
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188 | This option does not affect "encode" in any way - shared values and |
|
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189 | references will always be encoded properly if present. |
171 | |
190 | |
172 | $cbor = $cbor->pack_strings ([$enable]) |
191 | $cbor = $cbor->pack_strings ([$enable]) |
173 | $enabled = $cbor->get_pack_strings |
192 | $enabled = $cbor->get_pack_strings |
174 | If $enable is true (or missing), then "encode" will try not to |
193 | If $enable is true (or missing), then "encode" will try not to |
175 | encode the same string twice, but will instead encode a reference to |
194 | encode the same string twice, but will instead encode a reference to |
… | |
… | |
186 | the standard CBOR way. |
205 | the standard CBOR way. |
187 | |
206 | |
188 | This option does not affect "decode" in any way - string references |
207 | This option does not affect "decode" in any way - string references |
189 | will always be decoded properly if present. |
208 | will always be decoded properly if present. |
190 | |
209 | |
|
|
210 | $cbor = $cbor->validate_utf8 ([$enable]) |
|
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211 | $enabled = $cbor->get_validate_utf8 |
|
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212 | If $enable is true (or missing), then "decode" will validate that |
|
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213 | elements (text strings) containing UTF-8 data in fact contain valid |
|
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214 | UTF-8 data (instead of blindly accepting it). This validation |
|
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215 | obviously takes extra time during decoding. |
|
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216 | |
|
|
217 | The concept of "valid UTF-8" used is perl's concept, which is a |
|
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218 | superset of the official UTF-8. |
|
|
219 | |
|
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220 | If $enable is false (the default), then "decode" will blindly accept |
|
|
221 | UTF-8 data, marking them as valid UTF-8 in the resulting data |
|
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222 | structure regardless of whether thats true or not. |
|
|
223 | |
|
|
224 | Perl isn't too happy about corrupted UTF-8 in strings, but should |
|
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225 | generally not crash or do similarly evil things. Extensions might be |
|
|
226 | not so forgiving, so it's recommended to turn on this setting if you |
|
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227 | receive untrusted CBOR. |
|
|
228 | |
|
|
229 | This option does not affect "encode" in any way - strings that are |
|
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230 | supposedly valid UTF-8 will simply be dumped into the resulting CBOR |
|
|
231 | string without checking whether that is, in fact, true or not. |
|
|
232 | |
191 | $cbor = $cbor->filter ([$cb->($tag, $value)]) |
233 | $cbor = $cbor->filter ([$cb->($tag, $value)]) |
192 | $cb_or_undef = $cbor->get_filter |
234 | $cb_or_undef = $cbor->get_filter |
193 | Sets or replaces the tagged value decoding filter (when $cb is |
235 | Sets or replaces the tagged value decoding filter (when $cb is |
194 | specified) or clears the filter (if no argument or "undef" is |
236 | specified) or clears the filter (if no argument or "undef" is |
195 | provided). |
237 | provided). |
… | |
… | |
249 | protocol and you need to know where the first CBOR string ends amd |
291 | protocol and you need to know where the first CBOR string ends amd |
250 | the next one starts. |
292 | the next one starts. |
251 | |
293 | |
252 | CBOR::XS->new->decode_prefix ("......") |
294 | CBOR::XS->new->decode_prefix ("......") |
253 | => ("...", 3) |
295 | => ("...", 3) |
|
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296 | |
|
|
297 | INCREMENTAL PARSING |
|
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298 | In some cases, there is the need for incremental parsing of JSON texts. |
|
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299 | While this module always has to keep both CBOR text and resulting Perl |
|
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300 | data structure in memory at one time, it does allow you to parse a CBOR |
|
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301 | stream incrementally, using a similar to using "decode_prefix" to see if |
|
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302 | a full CBOR object is available, but is much more efficient. |
|
|
303 | |
|
|
304 | It basically works by parsing as much of a CBOR string as possible - if |
|
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305 | the CBOR data is not complete yet, the pasrer will remember where it |
|
|
306 | was, to be able to restart when more data has been accumulated. Once |
|
|
307 | enough data is available to either decode a complete CBOR value or raise |
|
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308 | an error, a real decode will be attempted. |
|
|
309 | |
|
|
310 | A typical use case would be a network protocol that consists of sending |
|
|
311 | and receiving CBOR-encoded messages. The solution that works with CBOR |
|
|
312 | and about anything else is by prepending a length to every CBOR value, |
|
|
313 | so the receiver knows how many octets to read. More compact (and |
|
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314 | slightly slower) would be to just send CBOR values back-to-back, as |
|
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315 | "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit |
|
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316 | length. |
|
|
317 | |
|
|
318 | The following methods help with this: |
|
|
319 | |
|
|
320 | @decoded = $cbor->incr_parse ($buffer) |
|
|
321 | This method attempts to decode exactly one CBOR value from the |
|
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322 | beginning of the given $buffer. The value is removed from the |
|
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323 | $buffer on success. When $buffer doesn't contain a complete value |
|
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324 | yet, it returns nothing. Finally, when the $buffer doesn't start |
|
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325 | with something that could ever be a valid CBOR value, it raises an |
|
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326 | exception, just as "decode" would. In the latter case the decoder |
|
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327 | state is undefined and must be reset before being able to parse |
|
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328 | further. |
|
|
329 | |
|
|
330 | This method modifies the $buffer in place. When no CBOR value can be |
|
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331 | decoded, the decoder stores the current string offset. On the next |
|
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332 | call, continues decoding at the place where it stopped before. For |
|
|
333 | this to make sense, the $buffer must begin with the same octets as |
|
|
334 | on previous unsuccessful calls. |
|
|
335 | |
|
|
336 | You can call this method in scalar context, in which case it either |
|
|
337 | returns a decoded value or "undef". This makes it impossible to |
|
|
338 | distinguish between CBOR null values (which decode to "undef") and |
|
|
339 | an unsuccessful decode, which is often acceptable. |
|
|
340 | |
|
|
341 | @decoded = $cbor->incr_parse_multiple ($buffer) |
|
|
342 | Same as "incr_parse", but attempts to decode as many CBOR values as |
|
|
343 | possible in one go, instead of at most one. Calls to "incr_parse" |
|
|
344 | and "incr_parse_multiple" can be interleaved. |
|
|
345 | |
|
|
346 | $cbor->incr_reset |
|
|
347 | Resets the incremental decoder. This throws away any saved state, so |
|
|
348 | that subsequent calls to "incr_parse" or "incr_parse_multiple" start |
|
|
349 | to parse a new CBOR value from the beginning of the $buffer again. |
|
|
350 | |
|
|
351 | This method can be caled at any time, but it *must* be called if you |
|
|
352 | want to change your $buffer or there was a decoding error and you |
|
|
353 | want to reuse the $cbor object for future incremental parsings. |
254 | |
354 | |
255 | MAPPING |
355 | MAPPING |
256 | This section describes how CBOR::XS maps Perl values to CBOR values and |
356 | This section describes how CBOR::XS maps Perl values to CBOR values and |
257 | vice versa. These mappings are designed to "do the right thing" in most |
357 | vice versa. These mappings are designed to "do the right thing" in most |
258 | circumstances automatically, preserving round-tripping characteristics |
358 | circumstances automatically, preserving round-tripping characteristics |
… | |
… | |
396 | the IEEE double format will be used. Perls that use formats other |
496 | the IEEE double format will be used. Perls that use formats other |
397 | than IEEE double to represent numerical values are supported, but |
497 | than IEEE double to represent numerical values are supported, but |
398 | might suffer loss of precision. |
498 | might suffer loss of precision. |
399 | |
499 | |
400 | OBJECT SERIALISATION |
500 | OBJECT SERIALISATION |
|
|
501 | This module implements both a CBOR-specific and the generic |
|
|
502 | Types::Serialier object serialisation protocol. The following |
|
|
503 | subsections explain both methods. |
|
|
504 | |
|
|
505 | ENCODING |
401 | This module knows two way to serialise a Perl object: The CBOR-specific |
506 | This module knows two way to serialise a Perl object: The CBOR-specific |
402 | way, and the generic way. |
507 | way, and the generic way. |
403 | |
508 | |
404 | Whenever the encoder encounters a Perl object that it cnanot serialise |
509 | Whenever the encoder encounters a Perl object that it cannot serialise |
405 | directly (most of them), it will first look up the "TO_CBOR" method on |
510 | directly (most of them), it will first look up the "TO_CBOR" method on |
406 | it. |
511 | it. |
407 | |
512 | |
408 | If it has a "TO_CBOR" method, it will call it with the object as only |
513 | If it has a "TO_CBOR" method, it will call it with the object as only |
409 | argument, and expects exactly one return value, which it will then |
514 | argument, and expects exactly one return value, which it will then |
… | |
… | |
414 | "CBOR" as the second argument, to distinguish it from other serialisers. |
519 | "CBOR" as the second argument, to distinguish it from other serialisers. |
415 | |
520 | |
416 | The "FREEZE" method can return any number of values (i.e. zero or more). |
521 | The "FREEZE" method can return any number of values (i.e. zero or more). |
417 | These will be encoded as CBOR perl object, together with the classname. |
522 | These will be encoded as CBOR perl object, together with the classname. |
418 | |
523 | |
|
|
524 | These methods *MUST NOT* change the data structure that is being |
|
|
525 | serialised. Failure to comply to this can result in memory corruption - |
|
|
526 | and worse. |
|
|
527 | |
419 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
528 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
420 | with an error. |
529 | with an error. |
421 | |
530 | |
|
|
531 | DECODING |
422 | Objects encoded via "TO_CBOR" cannot be automatically decoded, but |
532 | Objects encoded via "TO_CBOR" cannot (normally) be automatically |
423 | objects encoded via "FREEZE" can be decoded using the following |
533 | decoded, but objects encoded via "FREEZE" can be decoded using the |
424 | protocol: |
534 | following protocol: |
425 | |
535 | |
426 | When an encoded CBOR perl object is encountered by the decoder, it will |
536 | When an encoded CBOR perl object is encountered by the decoder, it will |
427 | look up the "THAW" method, by using the stored classname, and will fail |
537 | look up the "THAW" method, by using the stored classname, and will fail |
428 | if the method cannot be found. |
538 | if the method cannot be found. |
429 | |
539 | |
… | |
… | |
584 | 26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
694 | 26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
585 | These tags are automatically created (and decoded) for serialisable |
695 | These tags are automatically created (and decoded) for serialisable |
586 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
696 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
587 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
697 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
588 | |
698 | |
589 | 28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>) |
699 | 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>) |
590 | These tags are automatically decoded when encountered, resulting in |
700 | These tags are automatically decoded when encountered (and they do |
|
|
701 | not result in a cyclic data structure, see "allow_cycles"), |
591 | shared values in the decoded object. They are only encoded, however, |
702 | resulting in shared values in the decoded object. They are only |
592 | when "allow_sharable" is enabled. |
703 | encoded, however, when "allow_sharing" is enabled. |
|
|
704 | |
|
|
705 | Not all shared values can be successfully decoded: values that |
|
|
706 | reference themselves will *currently* decode as "undef" (this is not |
|
|
707 | the same as a reference pointing to itself, which will be |
|
|
708 | represented as a value that contains an indirect reference to itself |
|
|
709 | - these will be decoded properly). |
|
|
710 | |
|
|
711 | Note that considerably more shared value data structures can be |
|
|
712 | decoded than will be encoded - currently, only values pointed to by |
|
|
713 | references will be shared, others will not. While non-reference |
|
|
714 | shared values can be generated in Perl with some effort, they were |
|
|
715 | considered too unimportant to be supported in the encoder. The |
|
|
716 | decoder, however, will decode these values as shared values. |
593 | |
717 | |
594 | 256, 25 (stringref-namespace, stringref, L |
718 | 256, 25 (stringref-namespace, stringref, L |
595 | <http://cbor.schmorp.de/stringref>) |
719 | <http://cbor.schmorp.de/stringref>) |
596 | These tags are automatically decoded when encountered. They are only |
720 | These tags are automatically decoded when encountered. They are only |
597 | encoded, however, when "pack_strings" is enabled. |
721 | encoded, however, when "pack_strings" is enabled. |
… | |
… | |
615 | |
739 | |
616 | When any of these need to load additional modules that are not part of |
740 | When any of these need to load additional modules that are not part of |
617 | the perl core distribution (e.g. URI), it is (currently) up to the user |
741 | the perl core distribution (e.g. URI), it is (currently) up to the user |
618 | to provide these modules. The decoding usually fails with an exception |
742 | to provide these modules. The decoding usually fails with an exception |
619 | if the required module cannot be loaded. |
743 | if the required module cannot be loaded. |
|
|
744 | |
|
|
745 | 0, 1 (date/time string, seconds since the epoch) |
|
|
746 | These tags are decoded into Time::Piece objects. The corresponding |
|
|
747 | "Time::Piece::TO_CBOR" method always encodes into tag 1 values |
|
|
748 | currently. |
|
|
749 | |
|
|
750 | The Time::Piece API is generally surprisingly bad, and fractional |
|
|
751 | seconds are only accidentally kept intact, so watch out. On the plus |
|
|
752 | side, the module comes with perl since 5.10, which has to count for |
|
|
753 | something. |
620 | |
754 | |
621 | 2, 3 (positive/negative bignum) |
755 | 2, 3 (positive/negative bignum) |
622 | These tags are decoded into Math::BigInt objects. The corresponding |
756 | These tags are decoded into Math::BigInt objects. The corresponding |
623 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
757 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
624 | CBOR integers, and others into positive/negative CBOR bignums. |
758 | CBOR integers, and others into positive/negative CBOR bignums. |
… | |
… | |
703 | uses long double to represent floating point values, they might not be |
837 | uses long double to represent floating point values, they might not be |
704 | encoded properly. Half precision types are accepted, but not encoded. |
838 | encoded properly. Half precision types are accepted, but not encoded. |
705 | |
839 | |
706 | Strict mode and canonical mode are not implemented. |
840 | Strict mode and canonical mode are not implemented. |
707 | |
841 | |
|
|
842 | LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
|
|
843 | On perls that were built without 64 bit integer support (these are rare |
|
|
844 | nowadays, even on 32 bit architectures, as all major Perl distributions |
|
|
845 | are built with 64 bit integer support), support for any kind of 64 bit |
|
|
846 | integer in CBOR is very limited - most likely, these 64 bit values will |
|
|
847 | be truncated, corrupted, or otherwise not decoded correctly. This also |
|
|
848 | includes string, array and map sizes that are stored as 64 bit integers. |
|
|
849 | |
708 | THREADS |
850 | THREADS |
709 | This module is *not* guaranteed to be thread safe and there are no plans |
851 | This module is *not* guaranteed to be thread safe and there are no plans |
710 | to change this until Perl gets thread support (as opposed to the |
852 | to change this until Perl gets thread support (as opposed to the |
711 | horribly slow so-called "threads" which are simply slow and bloated |
853 | horribly slow so-called "threads" which are simply slow and bloated |
712 | process simulations - use fork, it's *much* faster, cheaper, better). |
854 | process simulations - use fork, it's *much* faster, cheaper, better). |