Debugging with GDB (September 2007)

Chapter 14: HP-UX Configuration-Specific Information 157
set thread check { [on|off]| [option] [on|off] |[option] [num]}
The set thread-check [on|off] command enables or disables advanced thread de-
bugging. This feature is off by default. The set thread-check [on|off] command
must be enabled prior to running the application under the debugger, to force the
underlying runtime system to collect information on pthread primitives.
The advanced thread debugging features can be enabled only if the set thread-check
[on] command is enabled. The following advanced thread debugging options are avail-
able for the set thread-check command:
• recursive-relock [on|off]
This set thread-check recursive-relock [on|off] com mand checks if a
thread has attempted to acquire a non-recursive mutex that it currently holds.
Re-locking a non-recursive mutex results in a deadlock. At run-time, the debugger
keeps track of each mutex in the application and the thread that currently holds
each mutex. When a thread attempts to acquire a lock on a non-recursive mutex,
the debugger checks if the thread currently holds the lock object for the mutex.
The debugger transfers the execution control to the user and prints a warning
message when this condition is detected.
• unlock-not-own [on|off]
The set thread-check unlock-not-own [on|off] command checks if a thread
has attempted to unlock a mutex or a read-write lock that it has not acquired.
The debugger transfers the execution control to the user and prints a warning
message when this condition is detected.
• mixed-sched-policy [on|off]
The set thread-check mixed-sched-policy [on|off] command checks if a
thread is waiting (blocked) on a mutex or a read-write lock that is held by
a thread with a different scheduling policy. This is not an application error
and does not always res ult in deadlock. However, it degrades the application
performance. The debugger transfers the execution control to the user and prints
a warning message when this condition is detected.
• cv-multiple-mxs [on|off]
The set thread-check cv-multiple-mxs [on|off] command checks if an ap-
plication uses the same condition variable in multiple calls, by different threads
to pthread_cond_wait() or pthread_cond_timedwait(), but specifies different
mutexes. The debugger transfers the execution control to the user and prints a
warning message when this condition is detected.
All threads that concurrently wait on any single condition variable must specify
the same associated mutex. For example,the pthread impleme ntation does not
allow thread 1 to wait on condition variable A by specifying mutex A, while
thread 2 waits on the same condition variable A by specifying mutex B. This
returns an EINVAL error to the application. In contrast to this obvious EINVAL
error, the cv-multiple-mxs option detects the less-obvious and non-concurrent
use of multiple mutexes with the same condition variable by different threads. This
option detects potential EINVAL errors that exist as a result of different timings or
execution paths.