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Truly independent web browser
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kleines Filmröllchen 49d29c8298 AK: Rehash HashTable in-place instead of shrinking 
As seen on TV, HashTable can get "thrashed", i.e. it has a bunch of
deleted buckets that count towards the load factor. This means that hash
tables which are large enough for their contents need to be resized.
This was fixed in 9d8da16 with a workaround that shrinks the HashTable
back down in these cases, as after the resize and re-hash the load
factor is very low again. However, that's not a good solution. If you
insert and remove repeatedly around a size boundary, you might get
frequent resizes, which involve frequent re-allocations.

The new solution is an in-place rehashing algorithm that I came up with.
(Do complain to me, I'm at fault.) Basically, it iterates the buckets
and re-hashes the used buckets while marking the deleted slots empty.
The issue arises with collisions in the re-hash. For this reason, there
are two kinds of used buckets during the re-hashing: the normal "used"
buckets, which are old and are treated as free space, and the
"re-hashed" buckets, which are new and treated as used space, i.e. they
trigger probing. Therefore, the procedure for relocating a bucket's
contents is as follows:
- Locate the "real" bucket of the contents with the hash. That bucket is
  the starting point for the target bucket, and the current (old) bucket
  is the bucket we want to move.
- While we still need to move the bucket:
  - If we're the target, something strange happened last iteration or we
    just re-hashed to the same location. We're done.
  - If the target is empty or deleted, just move the bucket. We're done.
  - If the target is a re-hashed full bucket, we probe by double-hashing
    our hash as usual. Henceforth, we move our target for the next
    iteration.
  - If the target is an old full bucket, we swap the target and to-move
buckets. Therefore, the bucket to move is a the correct location and the
former target, which still needs to find a new place, is now in the
bucket to move. So we can just continue with the loop; the target is
re-obtained from the bucket to move. This happens for each and every
bucket, though some buckets are "coincidentally" moved before their
point of iteration is reached. Either way, this guarantees full in-place
movement (even without stack storage) and therefore space complexity of
O(1). Time complexity is amortized O(2n) asssuming a good hashing
function.

This leads to a performance improvement of ~30% on the benchmark
introduced with the last commit.

Co-authored-by: Hendiadyoin1 <leon.a@serenityos.org>
2022-03-31 12:06:13 +02:00
.github Meta: Ignore the return value of test-wasm on CI 2022-03-17 23:20:06 +03:30
AK AK: Rehash HashTable in-place instead of shrinking 2022-03-31 12:06:13 +02:00
Base LibWeb: Fix sizing of flex child that has flex-basis 0 2022-03-30 21:16:47 +02:00
Documentation Everywhere: Move tests to /home/anon/Tests 2022-03-20 22:20:59 +01:00
Kernel Kernel: Fix storage device read/write for request length < block size 2022-03-30 19:31:12 +03:00
Meta LibWeb: Replace ad-hoc EventHandler type with callback function typedef 2022-03-31 01:10:47 +02:00
Ports Ports: Add Jagged Alliance 2 Stracciatella port 2022-03-30 14:11:53 +01:00
Tests Tests: Introduce a HashTable benchmark for "table thrashing" 2022-03-31 12:06:13 +02:00
Toolchain Toolchain: Fix serenity.nix 2022-03-29 16:36:28 -07:00
Userland LibELF: Remove unused m_program_interpreter member from DynamicLoader 2022-03-31 10:18:07 +02:00
.clang-format Meta: Update .clang-format to not indent nested namespaces 2020-03-14 10:10:21 +01:00
.clang-tidy Meta: Disable readability-use-anyofallof clang-tidy check 2022-01-09 23:29:57 -08:00
.gitattributes Repository: Protect port patches from CRLF/LF normalization 2022-01-12 01:08:38 +01:00
.gitignore man.serenityos.org: Simplify local builds 2021-10-22 19:49:28 +03:00
.mailmap Meta: Fix my .mailmap entry by adding the name 2022-01-25 23:26:14 +00:00
.pre-commit-config.yaml Meta: Add a post-commit commit message linter hook 2021-05-02 16:28:01 +02:00
.prettierignore CI: Bump prettier to latest version (2.4.1) 2021-11-21 01:18:23 +00:00
.prettierrc Meta: Move prettier config files to the root of the repository 2020-08-24 18:21:33 +02:00
azure-pipelines.yml CI: Disallow test failures on macOS Lagom :^) 2022-01-14 22:39:06 +01:00
CMakeLists.txt Meta: Error out on find_program errors with CMake less than 3.18 2022-03-19 15:01:22 -07:00
CONTRIBUTING.md Meta: Add Tim Flynn to list of project maintainers :^) 2022-02-11 22:24:10 +01:00
LICENSE Meta: Update year range in LICENSE :^) 2022-01-02 18:08:02 +01:00
README.md Meta: Add Maciej (sppmacd) to the contributors list :^) 2022-03-24 11:55:37 +01:00

README.md

SerenityOS

Graphical Unix-like operating system for x86 computers.

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About

SerenityOS is a love letter to '90s user interfaces with a custom Unix-like core. It flatters with sincerity by stealing beautiful ideas from various other systems.

Roughly speaking, the goal is a marriage between the aesthetic of late-1990s productivity software and the power-user accessibility of late-2000s *nix. This is a system by us, for us, based on the things we like.

You can watch videos of the system being developed on YouTube:

Screenshot

Screenshot as of b36968c.png

Kernel features

  • x86 (32-bit) and x86_64 (64-bit) kernel with pre-emptive multi-threading
  • Hardware protections (SMEP, SMAP, UMIP, NX, WP, TSD, ...)
  • IPv4 stack with ARP, TCP, UDP and ICMP protocols
  • ext2 filesystem
  • POSIX signals
  • Purgeable memory
  • /proc filesystem
  • Pseudoterminals (with /dev/pts filesystem)
  • Filesystem notifications
  • CPU and memory profiling
  • VMWare/QEMU mouse integration

System services

  • Launch/session daemon (SystemServer)
  • Compositing window server (WindowServer)
  • Text console manager (TTYServer)
  • DNS client (LookupServer)
  • Network protocols server (RequestServer and WebSocket)
  • Software-mixing sound daemon (AudioServer)
  • Desktop notifications (NotificationServer)
  • HTTP server (WebServer)
  • Telnet server (TelnetServer)
  • DHCP client (DHCPClient)

Libraries

  • C++ templates and containers (AK)
  • Event loop and utilities (LibCore)
  • 2D graphics library (LibGfx)
  • OpenGL 1.x compatible library (LibGL)
  • GUI toolkit (LibGUI)
  • Cross-process communication library (LibIPC)
  • HTML/CSS engine (LibWeb)
  • JavaScript engine (LibJS)
  • Markdown (LibMarkdown)
  • Audio (LibAudio)
  • Digital Signal Processing/Synthesizer Chains (LibDSP)
  • PCI database (LibPCIDB)
  • Terminal emulation (LibVT)
  • Out-of-process network protocol I/O (LibProtocol)
  • Mathematical functions (LibM)
  • ELF file handling (LibELF)
  • POSIX threading (LibPthread)
  • Higher-level threading (LibThreading)
  • Transport Layer Security (LibTLS)
  • HTTP and HTTPS (LibHTTP)
  • IMAP (LibIMAP)

Userland features

  • Unix-like libc and userland
  • Shell with pipes and I/O redirection
  • On-line help system (both terminal and GUI variants)
  • Web browser (Browser)
  • C++ IDE (HackStudio)
  • Desktop synthesizer (Piano)
  • E-mail client (Mail)
  • Various desktop apps & games
  • Color themes

How do I read the documentation?

Man pages are available online at man.serenityos.org. These pages are generated from the Markdown source files in Base/usr/share/man and updated automatically.

When running SerenityOS you can use man for the terminal interface, or help for the GUI.

How do I build and run this?

See the SerenityOS build instructions

Before opening an issue

Please see the issue policy.

FAQ: Frequently Asked Questions

Get in touch

Join our Discord server: SerenityOS Discord

Author

Contributors

(And many more!) The people listed above have landed more than 100 commits in the project. :^)

License

SerenityOS is licensed under a 2-clause BSD license.