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Detangler 0.2 (Default branch)
06-18-2008
Detangler is a Java Swing thread debugger. It solves problems such as incomplete and incorrect displays, events happening in the wrong order, gray windows, lockups, and slow response that gets slower with more use. These symptoms are usually caused by incorrect Swing threading, and thread bugs are the hardest to find. Detangler finds those tough bugs for you so that your application runs smoothly and quickly. License: Other/Proprietary License with Free Trial Changes:|
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WITNESS(4) BSD Kernel Interfaces Manual WITNESS(4) NAME
witness -- lock validation facility SYNOPSIS
options WITNESS options WITNESS_COUNT options WITNESS_KDB options WITNESS_NO_VNODE options WITNESS_SKIPSPIN DESCRIPTION
The witness module keeps track of the locks acquired and released by each thread. It also keeps track of the order in which locks are acquired with respect to each other. Each time a lock is acquired, witness uses these two lists to verify that a lock is not being acquired in the wrong order. If a lock order violation is detected, then a message is output to the kernel console detailing the locks involved and the locations in question. Witness can also be configured to drop into the kernel debugger when an order violation occurs. The witness code also checks various other conditions such as verifying that one does not recurse on a non-recursive lock, or attempt an upgrade on a shared lock held by another thread. If any of these checks fail, then the kernel will panic. The WITNESS_COUNT kernel option controls the maximum number of witness(4) entries that are tracked in the kernel. The maximum number of entries can be queried via the debug.witness.count sysctl. It can also be set from the loader(8) via the debug.witness.count environment variable. The WITNESS_NO_VNODE kernel option tells witness(4) to ignore locking issues between vnode(9) objects. The flag that controls whether or not the kernel debugger is entered when a lock order violation is detected can be set in a variety of ways. By default, the flag is off, but if the WITNESS_KDB kernel option is specified, then the flag will default to on. It can also be set from the loader(8) via the debug.witness.kdb environment variable or after the kernel has booted via the debug.witness.kdb sysctl. If the flag is set to zero, then the debugger will not be entered. If the flag is non-zero, then the debugger will be entered. The witness code can also be configured to skip all checks on spin mutexes. By default, this flag defaults to off, but it can be turned on by specifying the WITNESS_SKIPSPIN kernel option. The flag can also be set via the loader(8) environment variable debug.witness.skipspin. If the variable is set to a non-zero value, then spin mutexes are skipped. Once the kernel has booted, the status of this flag can be exam- ined but not set via the read-only sysctl debug.witness.skipspin. The sysctl debug.witness.watch specifies the level of witness involvement in the system. A value of 1 specifies that witness is enabled. A value of 0 specifies that witness is disabled, but that can be enabled again. This will maintain a small amount of overhead in the system. A value of -1 specifies that witness is disabled permanently and cannot be enabled again. The sysctl debug.witness.watch can be set via loader(8). The witness code also provides two extra ddb(4) commands if both witness and ddb(4) are compiled into the kernel: show locks [thread] Outputs the list of locks held by a thread to the kernel console along with the filename and line number at which each lock was last acquired by the thread. The optional thread argument may be either a TID, PID, or pointer to a thread structure. If thread is not specified, then the locks held by the current thread are displayed. show all locks Outputs the list of locks held by all threads in the system to the kernel console. show witness Dump the current order list to the kernel console. The code first displays the lock order tree for all of the sleep locks. Then it displays the lock order tree for all of the spin locks. Finally, it displays a list of locks that have not yet been acquired. SEE ALSO
ddb(4), loader(8), sysctl(8), mutex(9) HISTORY
The witness code first appeared in BSD/OS 5.0 and was imported from there into FreeBSD 5.0. BSD
February 6, 2015 BSD