man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

td_sync_setstate(3C_DB)

Name

td_sync_get_info, td_ta_sync_tracking_enable, td_sync_get_stats, td_sync_setstate, td_sync_waiters - operations on a synchronization object in libc_db

Synopsis

cc [ flag... ] file... -lc_db [ library... ]
#include <proc_service.h>
#include <thread_db.h>

td_err_e td_sync_get_info(const td_synchandle_t *sh_p, td_syncinfo_t *si_p);
td_err_e td_ta_sync_tracking_enable(const td_thragent_t *ta_p, int on_off);
td_err_e td_sync_get_stats(const td_synchandle_t *sh_p, td_syncstats_t *ss_p);
td_err_e td_sync_setstate(const td_synchandle_t *sh_p);
typedef int td_thr_iter_f(const td_thrhandle_t *th_p, void *cb_data_p);
td_err_e td_sync_waiters(const td_synchandle_t *sh_p, td_thr_iter_f *cb,
     void *cb_data_p);

Description

Synchronization objects include mutexes, condition variables, semaphores, and reader-writer locks. In the same way that thread operations use a thread handle of type td_thrhandle_t, operations on synchronization objects use a synchronization object handle of type td_synchandle_t .

The controlling process obtains synchronization object handles either by calling the function td_ta_sync_iter() to obtain handles for all synchronization objects of the target process that are known to the libc_db library of interfaces, or by mapping the address of a synchronization object in the address space of the target process to a handle by calling td_ta_map_addr2sync(3C_DB).

Not all synchronization objects that a process uses can be known to the libc_db library and returned by td_ta_sync_iter(3C_DB). A synchronization object is known to libc_db only if it has been the target of a synchronization primitive in the process (such as mutex_lock(), described on the mutex_init(3C) manual page) after td_ta_new(3C_DB) has been called to attach to the process and td_ta_sync_tracking_enable () has been called to enable synchronization object tracking.

The td_ta_sync_tracking_enable() function turns synchronization object tracking on or off for the process identified by ta_p, depending on whether on_off is 0 (off) or non-zero (on).

The td_sync_get_info() function fills in the td_syncinfo_t structure *si_p with values for the synchronization object identified by sh_p. The td_syncinfo_t structure contains the following fields:

td_thragent_t *si_ta_p

The internal process handle identifying the target process through which this synchronization object handle was obtained. Synchronization objects may be process-private or process-shared. In the latter case, the same synchronization object may have multiple handles, one for each target process's "view" of the synchronization object.

psaddr_t si_sv_addr

The address of the synchronization object in this target process's address space.

td_sync_type_e si_type

The type of the synchronization variable: mutex, condition variable, semaphore, or readers-writer lock.

int si_shared_type

If si_shared_type is non-zero, this synchronization object is process-shared, otherwise it is process-private.

td_sync_flags_t si_flags

Flags dependent on the type of the synchronization object.

int si_state.sema_count

Semaphores only. The current value of the semaphore

int si_state.nreaders

Readers-writer locks only. The number of readers currently holding the lock, or -1, if a writer is currently holding the lock.

int si_state.mutex_locked

For mutexes only. Non-zero if and only if the mutex is currently locked.

int si_size

The size of the synchronization object.

uint8_t si_has_waiters

Non-zero if and only if at least one thread is blocked on this synchronization object.

uint8_t si_is_wlocked

For reader-writer locks only. The value is non-zero if and only if this lock is held by a writer.

uint8_t si_rcount

PTHREAD_MUTEX_RECURSIVE mutexes only. If the mutex is held, the recursion count.

uint8_t si_prioceiling

PTHREAD_PRIO_PROTECT protocol mutexes only. The priority ceiling.

td_thrhandle_t si_owner

Mutexes and readers-writer locks only. This is the thread holding the mutex, or the write lock, if this is a reader-writer lock. The value is NULL if no one holds the mutex or write-lock.

pid_t si_ownerpid

Mutexes only. For a locked process-shared mutex, this is the process-ID of the process containing the owning thread.

The td_sync_get_stats() function fills in the td_syncstats_t structure *ss_p with values for the synchronization object identified by sh_p. The td_syncstats_t structure contains an embedded td_syncinfo_t structure that is filled in as described above for td_sync_get_info(). In addition, usage statistics gathered since td_ta_sync_tracking_enable() was called to enable synchronization object tracking are returned in the ss_un.mutex, ss_un.cond, ss_un.rwlock, or ss_un.sema members of the td_syncstats_t structure, depending on the type of the synchronization object.

The td_sync_setstate function modifies the state of synchronization object si_p, depending on the synchronization object type. For mutexes, td_sync_setstate is unlocked if the value is 0. Otherwise it is locked. For semaphores, the semaphore's count is set to the value. For reader-writer locks, the reader count set to the value if value is >0. The count is set to write-locked if value is –1. It is set to unlocked if the value is 0. Setting the state of a synchronization object from a libc_db interface may cause the synchronization object's semantics to be violated from the point of view of the threads in the target process. For example, if a thread holds a mutex, and td_sync_setstate is used to set the mutex to unlocked, then a different thread will also be able to subsequently acquire the same mutex.

The td_sync_waiters function iterates over the set of thread handles of threads blocked on sh_p. The callback function cb is called once for each such thread handle, and is passed the thread handle and cb_data_p. If the callback function returns a non-zero value, iteration is terminated early. See td_ta_thr_iter(3C_DB).

Return Values

TD_OK

The call returned successfully.

TD_BADTH

An invalid thread handle was passed in.

TD_DBERR

A call to one of the imported interface routines failed.

TD_ERR

A libc_db-internal error occurred.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
MT-Level
Safe

See Also

libc_db(3LIB), mutex_init(3C), td_ta_map_addr2sync(3C_DB), td_ta_sync_iter(3C_DB), td_ta_thr_iter(3C_DB), attributes(5)