@@ -43,13 +44,15 @@ JIT support applies only to the traditional Perl-compa It does not apply when the DFA matching function is being used. The code for this support was written by Zoltan Herczeg.
--JIT support is available for both the 8-bit and 16-bit PCRE libraries. To keep -this documentation simple, only the 8-bit interface is described in what -follows. If you are using the 16-bit library, substitute the 16-bit functions -and 16-bit structures (for example, pcre16_jit_stack instead of -pcre_jit_stack). +JIT support is available for all of the 8-bit, 16-bit and 32-bit PCRE +libraries. To keep this documentation simple, only the 8-bit interface is +described in what follows. If you are using the 16-bit library, substitute the +16-bit functions and 16-bit structures (for example, pcre16_jit_stack +instead of pcre_jit_stack). If you are using the 32-bit library, +substitute the 32-bit functions and 32-bit structures (for example, +pcre32_jit_stack instead of pcre_jit_stack).
@@ -61,17 +64,18 @@ JIT. The support is limited to the following hardware Intel x86 32-bit and 64-bit MIPS 32-bit Power PC 32-bit and 64-bit + SPARC 32-bit (experimental) -The Power PC support is designated as experimental because it has not been -fully tested. If --enable-jit is set on an unsupported platform, compilation -fails. +If --enable-jit is set on an unsupported platform, compilation fails.
A program that is linked with PCRE 8.20 or later can tell if JIT support is available by calling pcre_config() with the PCRE_CONFIG_JIT option. The result is 1 when JIT is available, and 0 otherwise. However, a simple program -does not need to check this in order to use JIT. The API is implemented in a -way that falls back to the ordinary PCRE code if JIT is not available. +does not need to check this in order to use JIT. The normal API is implemented +in a way that falls back to the interpretive code if JIT is not available. For +programs that need the best possible performance, there is also a "fast path" +API that is JIT-specific.
If your program may sometimes be linked with versions of PCRE that are older @@ -88,8 +92,8 @@ You have to do two things to make use of the JIT suppo pcre_exec(). (2) Use pcre_free_study() to free the pcre_extra block when it is - no longer needed instead of just freeing it yourself. This - ensures that any JIT data is also freed. + no longer needed, instead of just freeing it yourself. This ensures that + any JIT data is also freed. For a program that may be linked with pre-8.20 versions of PCRE, you can insert
@@ -106,32 +110,55 @@ this to free the study data:
pcre_free(study_ptr);
#endif
+PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for complete
+matches. If you want to run partial matches using the PCRE_PARTIAL_HARD or
+PCRE_PARTIAL_SOFT options of pcre_exec(), you should set one or both of
+the following options in addition to, or instead of, PCRE_STUDY_JIT_COMPILE
+when you call pcre_study():
++ PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE + PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE ++The JIT compiler generates different optimized code for each of the three +modes (normal, soft partial, hard partial). When pcre_exec() is called, +the appropriate code is run if it is available. Otherwise, the pattern is +matched using interpretive code. + +
In some circumstances you may need to call additional functions. These are described in the section entitled "Controlling the JIT stack" below.
-If JIT support is not available, PCRE_STUDY_JIT_COMPILE is ignored, and no JIT -data is set up. Otherwise, the compiled pattern is passed to the JIT compiler, -which turns it into machine code that executes much faster than the normal -interpretive code. When pcre_exec() is passed a pcre_extra block -containing a pointer to JIT code, it obeys that instead of the normal code. The -result is identical, but the code runs much faster. +If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are ignored, and +no JIT data is created. Otherwise, the compiled pattern is passed to the JIT +compiler, which turns it into machine code that executes much faster than the +normal interpretive code. When pcre_exec() is passed a pcre_extra +block containing a pointer to JIT code of the appropriate mode (normal or +hard/soft partial), it obeys that code instead of running the interpreter. The +result is identical, but the compiled JIT code runs much faster.
There are some pcre_exec() options that are not supported for JIT execution. There are also some pattern items that JIT cannot handle. Details are given below. In both cases, execution automatically falls back to the -interpretive code. +interpretive code. If you want to know whether JIT was actually used for a +particular match, you should arrange for a JIT callback function to be set up +as described in the section entitled +"Controlling the JIT stack" +below, even if you do not need to supply a non-default JIT stack. Such a +callback function is called whenever JIT code is about to be obeyed. If the +execution options are not right for JIT execution, the callback function is not +obeyed.
If the JIT compiler finds an unsupported item, no JIT data is generated. You can find out if JIT execution is available after studying a pattern by calling pcre_fullinfo() with the PCRE_INFO_JIT option. A result of 1 means that JIT compilation was successful. A result of 0 means that JIT support is not -available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE, or the -JIT compiler was not able to handle the pattern. +available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE etc., or +the JIT compiler was not able to handle the pattern.
Once a pattern has been studied, with or without JIT, it can be used as many
@@ -140,22 +167,14 @@ times as you like for matching different subject strin
UNSUPPORTED OPTIONS AND PATTERN ITEMS
The only pcre_exec() options that are supported for JIT execution are -PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and -PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not -supported. +PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NO_UTF32_CHECK, PCRE_NOTBOL, +PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and +PCRE_PARTIAL_SOFT.
-The unsupported pattern items are: -
- \C match a single byte; not supported in UTF-8 mode - (?Cn) callouts - (*COMMIT) ) - (*MARK) ) - (*PRUNE) ) the backtracking control verbs - (*SKIP) ) - (*THEN) ) --Support for some of these may be added in future. +The only unsupported pattern items are \C (match a single data unit) when +running in a UTF mode, and a callout immediately before an assertion condition +in a conditional group.
@@ -221,8 +240,8 @@ should use. Its arguments are as follows: void *data The extra argument must be the result of studying a pattern with -PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the other two -options: +PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the other +two options:
(1) If callback is NULL and data is NULL, an internal 32K block
on the machine stack is used.
@@ -230,26 +249,38 @@ options:
(2) If callback is NULL and data is not NULL, data must be
a valid JIT stack, the result of calling pcre_jit_stack_alloc().
- (3) If callback not NULL, it must point to a function that is called
- with data as an argument at the start of matching, in order to
- set up a JIT stack. If the result is NULL, the internal 32K stack
- is used; otherwise the return value must be a valid JIT stack,
- the result of calling pcre_jit_stack_alloc().
+ (3) If callback is not NULL, it must point to a function that is
+ called with data as an argument at the start of matching, in
+ order to set up a JIT stack. If the return from the callback
+ function is NULL, the internal 32K stack is used; otherwise the
+ return value must be a valid JIT stack, the result of calling
+ pcre_jit_stack_alloc().
-You may safely assign the same JIT stack to more than one pattern, as long as
-they are all matched sequentially in the same thread. In a multithread
-application, each thread must use its own JIT stack.
+A callback function is obeyed whenever JIT code is about to be run; it is not
+obeyed when pcre_exec() is called with options that are incompatible for
+JIT execution. A callback function can therefore be used to determine whether a
+match operation was executed by JIT or by the interpreter.
-Strictly speaking, even more is allowed. You can assign the same stack to any -number of patterns as long as they are not used for matching by multiple +You may safely use the same JIT stack for more than one pattern (either by +assigning directly or by callback), as long as the patterns are all matched +sequentially in the same thread. In a multithread application, if you do not +specify a JIT stack, or if you assign or pass back NULL from a callback, that +is thread-safe, because each thread has its own machine stack. However, if you +assign or pass back a non-NULL JIT stack, this must be a different stack for +each thread so that the application is thread-safe. +
++Strictly speaking, even more is allowed. You can assign the same non-NULL stack +to any number of patterns as long as they are not used for matching by multiple threads at the same time. For example, you can assign the same stack to all compiled patterns, and use a global mutex in the callback to wait until the -stack is available for use. However, this is an inefficient solution, and -not recommended. +stack is available for use. However, this is an inefficient solution, and not +recommended.
-This is a suggestion for how a typical multithreaded program might operate: +This is a suggestion for how a multithreaded program that needs to set up +non-default JIT stacks might operate:
During thread initalization
thread_local_var = pcre_jit_stack_alloc(...)
@@ -263,7 +294,7 @@ This is a suggestion for how a typical multithreaded p
All the functions described in this section do nothing if JIT is not available,
and pcre_assign_jit_stack() does nothing unless the extra argument
is non-NULL and points to a pcre_extra block that is the result of a
-successful study with PCRE_STUDY_JIT_COMPILE.
+successful study with PCRE_STUDY_JIT_COMPILE etc.
JIT STACK FAQ
@@ -320,7 +351,7 @@ replacement.
No, because this is too costly in terms of resources. However, you could
implement some clever idea which release the stack if it is not used in let's
-say two minutes. The JIT callback can help to achive this without keeping a
+say two minutes. The JIT callback can help to achieve this without keeping a
list of the currently JIT studied patterns.
@@ -329,11 +360,11 @@ pattern causes stack overflow with a stack of 1M? Is t
stack is freed?
-Especially on embedded sytems, it might be a good idea to release
-memory sometimes without freeing the stack. There is no API for this at the
-moment. Probably a function call which returns with the currently allocated
-memory for any stack and another which allows releasing memory (shrinking the
-stack) would be a good idea if someone needs this.
+Especially on embedded sytems, it might be a good idea to release memory
+sometimes without freeing the stack. There is no API for this at the moment.
+Probably a function call which returns with the currently allocated memory for
+any stack and another which allows releasing memory (shrinking the stack) would
+be a good idea if someone needs this.
(7) This is too much of a headache. Isn't there any better solution for JIT
@@ -368,11 +399,40 @@ callback.
-+Because the API described above falls back to interpreted execution when JIT is +not available, it is convenient for programs that are written for general use +in many environments. However, calling JIT via pcre_exec() does have a +performance impact. Programs that are written for use where JIT is known to be +available, and which need the best possible performance, can instead use a +"fast path" API to call JIT execution directly instead of calling +pcre_exec() (obviously only for patterns that have been successfully +studied by JIT). +
++The fast path function is called pcre_jit_exec(), and it takes exactly +the same arguments as pcre_exec(), plus one additional argument that +must point to a JIT stack. The JIT stack arrangements described above do not +apply. The return values are the same as for pcre_exec(). +
++When you call pcre_exec(), as well as testing for invalid options, a +number of other sanity checks are performed on the arguments. For example, if +the subject pointer is NULL, or its length is negative, an immediate error is +given. Also, unless PCRE_NO_UTF[8|16|32] is set, a UTF subject string is tested +for validity. In the interests of speed, these checks do not happen on the JIT +fast path, and if invalid data is passed, the result is undefined. +
++Bypassing the sanity checks and the pcre_exec() wrapping can give +speedups of more than 10%. +
+pcreapi(3)
-
Philip Hazel (FAQ by Zoltan Herczeg)
@@ -381,11 +441,11 @@ University Computing Service
Cambridge CB2 3QH, England.
-Last updated: 08 January 2012
+Last updated: 17 March 2013
-Copyright © 1997-2012 University of Cambridge.
+Copyright © 1997-2013 University of Cambridge.
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