2c588b031f
Consider this scenario: * A userland thread puts its ID into some structure so that it can be woken up later, sets its wait_status to initiate the begin of the wait, and then calls _user_block_thread. * A second thread finishes whatever task the first thread intended to wait for, reads the ID almost immediately after it was written, and calls _user_unblock_thread. * _user_unblock_thread was called so soon that the first thread is not yet blocked on the _user_block_thread block, but is instead blocked on e.g. the thread's main mutex. * The first thread's thread_block() call returns B_OK. As in this example it was inside mutex_lock, it thinks that it now owns the mutex. * But it doesn't own the mutex, and so (until yesterday) all sorts of mayhem and then a random crash occurs, or (after yesterday) an assert-failure is tripped that the thread does not own the mutex it expected to. The above scenario is not a hypothetical, but is in fact the exact scenario behind the strange panics in #15211. The solution is to only have _user_unblock_thread actually unblock threads that were blocked by _user_block_thread, so I've introduced a new BLOCK_TYPE to differentiate these. While I'm at it, remove the BLOCK_TYPE_USER_BASE, which was never used (and now never will be.) If we want to differentiate different consumers of _user_block_thread for debugging purposes, we should use the currently-unused "object" argument to thread_block, instead of cluttering the relatively-clean block type debugging code with special types. One final note: The race condition which was the case of this bug does not, in fact, imply a deadlock on the part of the rw_lock here. The wait_status is protected by the thread's mutex, which is acquired by both _user_block_thread and _user_unblock_thread, and so if _user_unblock_thread succeeds faster than _user_block_thread can initiate the block, it will just see that wait_status is already <= 0 and return immediately. Fixes #15211. |
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| ReadMe.Compiling.md | ||
| ReadMe.md | ||
Haiku
Homepage | Mailing Lists | IRC Channels | Issue Tracker | API docs
Haiku is an open-source operating system that specifically targets personal computing. Inspired by the BeOS, Haiku is fast, simple to use, easy to learn and yet very powerful.
Goals
- Sensible defaults with minimal configuration required.
- Clean, clear, concise code.
- Unified desktop environment.
Trying Haiku
Haiku provides pre-built nightly images and release images. Haiku is compatible with a large variety of hardware, but in case you don't want to "take the plunge" and install Haiku on bare metal, you can install it on a virtual machine (VM) instead. If you've never used a VM before, you can follow one of the "Emulating Haiku" guides.
Compiling Haiku
See ReadMe.Compiling.
Contributing
Haiku is a meritocratic open source project with a large variety of tasks. Even if you can't write code, you can still help! Haiku needs designers, (technical) writers, translators, testers... Get involved and help out!
Contributing code
If you're submitting a patch to us, please make sure you're following the patch submitting guidelines.
If you're having trouble finding something in the source tree, you can use one of our OpenGrok servers:
- http://xref.plausible.coop/ (provided by Landon Fuller)
- http://code.metager.de/source/xref/haiku (provided by MetaGer)
Contributing documentation
The main piece of documentation that still needs work are the API docs (found
in the tree at docs/user). Just find an undocumented class, write
documentation for it, and submit a patch.
Contributing translations
See wiki:i18n.
Contributing software ports
See HaikuPorts.
Contributing to our infrastructure
See Infrastructure.