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198 lines
8.7 KiB
198 lines
8.7 KiB
.TH PCRE2SERIALIZE 3 "27 June 2018" "PCRE2 10.32"
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.SH NAME
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PCRE2 - Perl-compatible regular expressions (revised API)
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.SH "SAVING AND RE-USING PRECOMPILED PCRE2 PATTERNS"
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.rs
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.sp
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.nf
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.B int32_t pcre2_serialize_decode(pcre2_code **\fIcodes\fP,
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.B " int32_t \fInumber_of_codes\fP, const uint8_t *\fIbytes\fP,"
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.B " pcre2_general_context *\fIgcontext\fP);"
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.sp
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.B int32_t pcre2_serialize_encode(const pcre2_code **\fIcodes\fP,
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.B " int32_t \fInumber_of_codes\fP, uint8_t **\fIserialized_bytes\fP,"
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.B " PCRE2_SIZE *\fIserialized_size\fP, pcre2_general_context *\fIgcontext\fP);"
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.sp
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.B void pcre2_serialize_free(uint8_t *\fIbytes\fP);
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.sp
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.B int32_t pcre2_serialize_get_number_of_codes(const uint8_t *\fIbytes\fP);
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.fi
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.sp
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If you are running an application that uses a large number of regular
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expression patterns, it may be useful to store them in a precompiled form
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instead of having to compile them every time the application is run. However,
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if you are using the just-in-time optimization feature, it is not possible to
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save and reload the JIT data, because it is position-dependent. The host on
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which the patterns are reloaded must be running the same version of PCRE2, with
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the same code unit width, and must also have the same endianness, pointer width
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and PCRE2_SIZE type. For example, patterns compiled on a 32-bit system using
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PCRE2's 16-bit library cannot be reloaded on a 64-bit system, nor can they be
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reloaded using the 8-bit library.
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.P
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Note that "serialization" in PCRE2 does not convert compiled patterns to an
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abstract format like Java or .NET serialization. The serialized output is
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really just a bytecode dump, which is why it can only be reloaded in the same
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environment as the one that created it. Hence the restrictions mentioned above.
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Applications that are not statically linked with a fixed version of PCRE2 must
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be prepared to recompile patterns from their sources, in order to be immune to
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PCRE2 upgrades.
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.
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.
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.SH "SECURITY CONCERNS"
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.rs
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.sp
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The facility for saving and restoring compiled patterns is intended for use
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within individual applications. As such, the data supplied to
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\fBpcre2_serialize_decode()\fP is expected to be trusted data, not data from
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arbitrary external sources. There is only some simple consistency checking, not
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complete validation of what is being re-loaded. Corrupted data may cause
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undefined results. For example, if the length field of a pattern in the
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serialized data is corrupted, the deserializing code may read beyond the end of
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the byte stream that is passed to it.
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.
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.
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.SH "SAVING COMPILED PATTERNS"
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.rs
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.sp
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Before compiled patterns can be saved they must be serialized, which in PCRE2
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means converting the pattern to a stream of bytes. A single byte stream may
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contain any number of compiled patterns, but they must all use the same
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character tables. A single copy of the tables is included in the byte stream
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(its size is 1088 bytes). For more details of character tables, see the
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.\" HTML <a href="pcre2api.html#localesupport">
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.\" </a>
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section on locale support
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.\"
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in the
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.\" HREF
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\fBpcre2api\fP
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.\"
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documentation.
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.P
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The function \fBpcre2_serialize_encode()\fP creates a serialized byte stream
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from a list of compiled patterns. Its first two arguments specify the list,
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being a pointer to a vector of pointers to compiled patterns, and the length of
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the vector. The third and fourth arguments point to variables which are set to
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point to the created byte stream and its length, respectively. The final
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argument is a pointer to a general context, which can be used to specify custom
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memory management functions. If this argument is NULL, \fBmalloc()\fP is used
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to obtain memory for the byte stream. The yield of the function is the number
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of serialized patterns, or one of the following negative error codes:
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.sp
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PCRE2_ERROR_BADDATA the number of patterns is zero or less
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PCRE2_ERROR_BADMAGIC mismatch of id bytes in one of the patterns
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PCRE2_ERROR_NOMEMORY memory allocation failed
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PCRE2_ERROR_MIXEDTABLES the patterns do not all use the same tables
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PCRE2_ERROR_NULL the 1st, 3rd, or 4th argument is NULL
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.sp
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PCRE2_ERROR_BADMAGIC means either that a pattern's code has been corrupted, or
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that a slot in the vector does not point to a compiled pattern.
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.P
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Once a set of patterns has been serialized you can save the data in any
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appropriate manner. Here is sample code that compiles two patterns and writes
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them to a file. It assumes that the variable \fIfd\fP refers to a file that is
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open for output. The error checking that should be present in a real
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application has been omitted for simplicity.
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.sp
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int errorcode;
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uint8_t *bytes;
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PCRE2_SIZE erroroffset;
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PCRE2_SIZE bytescount;
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pcre2_code *list_of_codes[2];
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list_of_codes[0] = pcre2_compile("first pattern",
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PCRE2_ZERO_TERMINATED, 0, &errorcode, &erroroffset, NULL);
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list_of_codes[1] = pcre2_compile("second pattern",
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PCRE2_ZERO_TERMINATED, 0, &errorcode, &erroroffset, NULL);
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errorcode = pcre2_serialize_encode(list_of_codes, 2, &bytes,
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&bytescount, NULL);
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errorcode = fwrite(bytes, 1, bytescount, fd);
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.sp
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Note that the serialized data is binary data that may contain any of the 256
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possible byte values. On systems that make a distinction between binary and
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non-binary data, be sure that the file is opened for binary output.
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.P
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Serializing a set of patterns leaves the original data untouched, so they can
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still be used for matching. Their memory must eventually be freed in the usual
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way by calling \fBpcre2_code_free()\fP. When you have finished with the byte
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stream, it too must be freed by calling \fBpcre2_serialize_free()\fP. If this
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function is called with a NULL argument, it returns immediately without doing
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anything.
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.
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.
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.SH "RE-USING PRECOMPILED PATTERNS"
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.rs
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.sp
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In order to re-use a set of saved patterns you must first make the serialized
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byte stream available in main memory (for example, by reading from a file). The
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management of this memory block is up to the application. You can use the
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\fBpcre2_serialize_get_number_of_codes()\fP function to find out how many
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compiled patterns are in the serialized data without actually decoding the
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patterns:
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.sp
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uint8_t *bytes = <serialized data>;
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int32_t number_of_codes = pcre2_serialize_get_number_of_codes(bytes);
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.sp
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The \fBpcre2_serialize_decode()\fP function reads a byte stream and recreates
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the compiled patterns in new memory blocks, setting pointers to them in a
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vector. The first two arguments are a pointer to a suitable vector and its
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length, and the third argument points to a byte stream. The final argument is a
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pointer to a general context, which can be used to specify custom memory
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management functions for the decoded patterns. If this argument is NULL,
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\fBmalloc()\fP and \fBfree()\fP are used. After deserialization, the byte
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stream is no longer needed and can be discarded.
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.sp
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pcre2_code *list_of_codes[2];
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uint8_t *bytes = <serialized data>;
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int32_t number_of_codes =
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pcre2_serialize_decode(list_of_codes, 2, bytes, NULL);
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.sp
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If the vector is not large enough for all the patterns in the byte stream, it
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is filled with those that fit, and the remainder are ignored. The yield of the
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function is the number of decoded patterns, or one of the following negative
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error codes:
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.sp
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PCRE2_ERROR_BADDATA second argument is zero or less
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PCRE2_ERROR_BADMAGIC mismatch of id bytes in the data
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PCRE2_ERROR_BADMODE mismatch of code unit size or PCRE2 version
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PCRE2_ERROR_BADSERIALIZEDDATA other sanity check failure
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PCRE2_ERROR_MEMORY memory allocation failed
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PCRE2_ERROR_NULL first or third argument is NULL
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.sp
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PCRE2_ERROR_BADMAGIC may mean that the data is corrupt, or that it was compiled
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on a system with different endianness.
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.P
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Decoded patterns can be used for matching in the usual way, and must be freed
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by calling \fBpcre2_code_free()\fP. However, be aware that there is a potential
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race issue if you are using multiple patterns that were decoded from a single
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byte stream in a multithreaded application. A single copy of the character
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tables is used by all the decoded patterns and a reference count is used to
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arrange for its memory to be automatically freed when the last pattern is
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freed, but there is no locking on this reference count. Therefore, if you want
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to call \fBpcre2_code_free()\fP for these patterns in different threads, you
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must arrange your own locking, and ensure that \fBpcre2_code_free()\fP cannot
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be called by two threads at the same time.
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.P
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If a pattern was processed by \fBpcre2_jit_compile()\fP before being
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serialized, the JIT data is discarded and so is no longer available after a
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save/restore cycle. You can, however, process a restored pattern with
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\fBpcre2_jit_compile()\fP if you wish.
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.
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.
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.
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.SH AUTHOR
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.rs
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.sp
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.nf
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Philip Hazel
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Retired from University Computing Service
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Cambridge, England.
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.fi
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.
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.
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.SH REVISION
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.rs
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.sp
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.nf
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Last updated: 27 June 2018
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Copyright (c) 1997-2018 University of Cambridge.
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.fi
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