unix-ffi/re: Fix the PCRE2 memory leaks. - #1153
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Every call to search() allocated a match data block with pcre2_match_data_create_from_pattern() and never freed it again, leaking a few kilobytes per call, on the no-match path as well. Free it once the offsets have been copied out of it. The module level functions compile a pattern that the caller never gets to see, and that was leaked as well. Free it when the call is done; the match object that is returned does not refer to it. Note that a pattern returned by re.compile() still has to be kept alive by the caller and cannot be released automatically, because MicroPython does not run __del__ on instances of Python classes. Signed-off-by: Kirill Lukonin (Evil Wireless Man) <klukonin@gmail.com>
The error code and the error offset were passed as bytes(4). Such objects are immutable, and the error offset is a PCRE2_SIZE, which is 8 bytes on a 64-bit target, so a failing compile wrote 4 bytes past the end of the buffer. Use writable arrays of the right size instead, and report the values in the assertion. Signed-off-by: Kirill Lukonin (Evil Wireless Man) <klukonin@gmail.com>
The test measures the resident set size around a few thousand calls and fails if it keeps growing. It covers every entry point that makes PCRE2 allocate: matching with a compiled pattern, the module level functions, and compiling itself, including a pattern that fails to compile. Without the preceding fixes it reports between 4.6 and 17.8 kilobytes of growth per call, depending on the entry point. Signed-off-by: Kirill Lukonin (Evil Wireless Man) <klukonin@gmail.com>
Every call to re.search(), and to the functions next to it, compiled the pattern it was given. Keep the compiled patterns in a small cache instead, the way CPython does, so that using the same pattern again does not compile it a second time. compile() returns the cached pattern as well, so re.compile(p) is re.compile(p), as it is in CPython. Matching against a repeated pattern gets about twice as fast, compiling one about eight times. Because MicroPython cannot release a compiled pattern by itself, the cache also decides what is kept: a cached pattern stays for the lifetime of the program, and a pattern that this module compiled for its own use is freed again afterwards. The cache owns what it holds and never evicts it. A pattern that is still in use, by the caller or by a call further up the stack, must not be freed underneath it, which a replacement callback passed to sub() can otherwise trigger. The cache is bounded instead: once it is full, further patterns are compiled and, where this module owns them, freed again after use. Signed-off-by: Kirill Lukonin (Evil Wireless Man) <klukonin@gmail.com>
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unix-ffi/renever frees anything it gets from PCRE2. Every match leaks thematch data block, and every compiled pattern leaks as well, so a program or module (such as json) that
uses re module in a loop grows without bound.
Measured on a
ports/unixbuild (1.30.0-preview) against libpcre2-8, residentset size around 2x5000 calls:
Pattern.search(), match / no matchPattern.match()/sub()/split()/findall()re.search()/re.match()re.sub()/re.split()/re.findall()re.compile(), same patternre.compile(), distinct patterns70k operations grew the process from 4 MB to 367 MB before.
With the fixes it is flat now.