This PR introduces a basic transaction support for the new mpmc hashtable:

it introduces two new data structures, both mpmc and spsc, to fetch and release slot ids using a bitmap, whereas each slot is mapped to each bit of the bitmap
- this special bitmap uses a table lookup to quickly find which is the first bit available in an uint16_t drammatically reducing the number of comparisons the algorithm has to carry out
- the mpmc variant offers some additional functions over the spsc one to avoid cache-conflicts in the vast majority of the cases
it restructures the transactions related structs and fields, now the id is a plain uint32_t number
- it can even be reduced in size to recoup space to be used for different purposes, probably a 20 bit number would be plenty as having 1048575 transactions seems unlikely even on very high end systems
it updates the internal interfaces to provide the needed hooks and checks for the transactions needed for the Read-Modify-Write operations

This PR is extremely important because it introduces a blazing fast new data structure, the slots_bitmap_mpmc which performs extremely well under contention. The main idea is that each transaction is just a slot of the bitmap and each thread will search in this bitmap first in its own shard (as the bitmap allows localized searches) and then in the whole bitmaps as fallback.

The result is that in a normal situation, where slots are available for the thread, to acquire and release 51200 slots per threads it takes just a few nanoseconds (more details in benches/bench-slots-bitmap-mpmc.cpp)

threads:1 15099228 ns
threads:2 1027204 ns
threads:4 74470 ns
threads:8 5860 ns
threads:16 499 ns
threads:32 42 ns

With 4 thread and in avg 800k ops/s in total (therefore potentially 800k transactions/s) the time required would be 1.16ms, an average overhead of 1.45ns per transaction to be acquired and released meanwhile with with just 1 thread and in avg 200k ops/s would be 295us. In both cases the time to acquire and release a transaction id is close enough to zero to be considered irrelevant!

Codecov Report

Patch coverage: 94.95% and project coverage change: +0.15 :tada:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #285 +/- ## ========================================== + Coverage 83.01% 83.15% +0.15% ========================================== Files 158 161 +3 Lines 10310 10524 +214 ========================================== + Hits 8558 8751 +193 - Misses 1752 1773 +21 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `83.15% <94.95%> (+0.15%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano) | Coverage Δ | | |---|---|---| | [...rc/data\_structures/hashtable/spsc/hashtable\_spsc.c](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL2RhdGFfc3RydWN0dXJlcy9oYXNodGFibGUvc3BzYy9oYXNodGFibGVfc3BzYy5j) | `94.51% <ø> (ø)` | | | [...rc/data\_structures/hashtable\_mpmc/hashtable\_mpmc.c](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL2RhdGFfc3RydWN0dXJlcy9oYXNodGFibGVfbXBtYy9oYXNodGFibGVfbXBtYy5j) | `94.28% <80.00%> (+0.22%)` | :arrow_up: | | [...a\_structures/slots\_bitmap\_mpmc/slots\_bitmap\_mpmc.c](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL2RhdGFfc3RydWN0dXJlcy9zbG90c19iaXRtYXBfbXBtYy9zbG90c19iaXRtYXBfbXBtYy5j) | `94.03% <94.03%> (ø)` | | | [...a\_structures/slots\_bitmap\_spsc/slots\_bitmap\_spsc.c](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL2RhdGFfc3RydWN0dXJlcy9zbG90c19iaXRtYXBfc3BzYy9zbG90c19iaXRtYXBfc3BzYy5j) | `95.70% <95.70%> (ø)` | | | [...a\_structures/slots\_bitmap\_mpmc/slots\_bitmap\_mpmc.h](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL2RhdGFfc3RydWN0dXJlcy9zbG90c19iaXRtYXBfbXBtYy9zbG90c19iaXRtYXBfbXBtYy5o) | `96.97% <96.97%> (ø)` | | | [src/network/channel/network\_channel\_tls.c](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL25ldHdvcmsvY2hhbm5lbC9uZXR3b3JrX2NoYW5uZWxfdGxzLmM=) | `1.20% <0.00%> (-0.16%)` | :arrow_down: | | [src/network/network\_tls.c](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL25ldHdvcmsvbmV0d29ya190bHMuYw==) | `71.83% <0.00%> (ø)` | | | [src/network/io/network\_io\_common\_tls.c](https://codecov.io/gh/danielealbano/cachegrand/pull/285?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano#diff-c3JjL25ldHdvcmsvaW8vbmV0d29ya19pb19jb21tb25fdGxzLmM=) | `100.00% <0.00%> (+100.00%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Daniele+Salvatore+Albano)

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danielealbano / cachegrand

Initial implementation transactions in new hastable mpmc #285

Codecov Report