Statsd dictionaries should be multi-threaded (#13938)
* the new dictionaries do not support concurrent use without locks * update dictionaries readme
Costa Tsaousis committed
Nov 2, 2022 at 16:56 UTC
4aeb68234dabbb414a0b0c1599b670c02530b1c5
2 files changed
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collectors/statsd.plugin/statsd.c
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@@ -20,15 +20,10 @@
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// --------------------------------------------------------------------------------------
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+// DO NOT ENABLE MULTITHREADING - IT IS NOT WELL TESTED
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// #define STATSD_MULTITHREADED 1
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-#ifdef STATSD_MULTITHREADED
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-// DO NOT ENABLE MULTITHREADING - IT IS NOT WELL TESTED
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#define STATSD_DICTIONARY_OPTIONS (DICT_OPTION_DONT_OVERWRITE_VALUE | DICT_OPTION_ADD_IN_FRONT)
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-#else
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-#define STATSD_DICTIONARY_OPTIONS (DICT_OPTION_DONT_OVERWRITE_VALUE | DICT_OPTION_ADD_IN_FRONT | DICT_OPTION_SINGLE_THREADED)
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-#endif
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-
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#define STATSD_DECIMAL_DETAIL 1000 // floating point values get multiplied by this, with the same divisor
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// --------------------------------------------------------------------------------------------------------------------
libnetdata/dictionary/README.md
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@@ -229,12 +229,3 @@ There are 2 versions of `dfe_start`:
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While in the loop, depending on the read or write versions of `dfe_start`, the caller may lookup or manipulate the dictionary. The rules are the same with the unsorted walkthrough callback functions.
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PS: DFE is Dictionary For Each.
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-
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-## special multi-threaded lockless case
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-
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-Since the dictionary uses a hash table and a double linked list, if the contract between 2 threads is for one to use the hash table functions only (`set`, `get` - but no `del`) and the other to use the traversal ones only, the dictionary allows concurrent use without locks.
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-
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-This is currently used in statsd:
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-
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-- the data collection thread uses only `get` and `set`. It never uses `del`. New items are added at the front of the linked list (`DICT_OPTION_ADD_IN_FRONT`).
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-- the flushing thread is only traversing the dictionary up to the point it last traversed it (it uses a flag for that to know where it stopped last time). It never uses `get`, `set` or `del`.