Mutexes Page

A mutex is a mutual exclusion object that allows multiple threads to synchronize access to shared resources. A mutex has two states: locked and unlocked. Once a mutex is locked by a thread, other threads attempting to lock it will block. Only after a locking thread unlocks (releases) the mutex can one of the blocked threads acquire (lock) the mutex and proceed.

This page contains a list of all mutexes known in a process.

For each mutex, TotalView displays the following information:

ID

The sequence number assigned to a mutex by the threads package. Diving into this field opens a Variable Window containing a view of the mutex’s data.

Type

The mutex type. These types are set using the pthread_mutexattr_settype() call on the attribute object before the mutex is initialized.

The type is one of the following:

Normal

A normal mutex.

Recurs

A recursive mutex.

ErrChk

An error-check mutex.

NRecNP

A non-portable, non-recursive mutex.

RcurNP

A non-portable, recursive mutex.

FastNP

A non-portable, fast mutex.

State

The mutex lock state is displayed as follows:

Unlocked

The mutex is unlocked.

Locked

The mutex is locked. By default, this is shown in blue; its color is the same as the thread’s stopped state flag color.

Pshared

This value indicates if the mutex can be shared by other processes.

Private

The mutex can only be manipulated by threads in the process that initialized the mutex.

Shared

The mutex can be manipulated by any process that has access to the mutex’s memory. (Some versions of IBM’s system libraries cannot provide information on shared mutexes. If this information is not available, TotalView only describes private mutexes.)

Owner

If the mutex is locked, this field displays the locking thread’s system TID.

Diving on this number tells TotalView to display the locking thread’s Process Window. This is the same window that TotalView would display if you dive or select the thread's entry in the Root Window’s Attached Page.

If threads are waiting for this mutex, their system TIDs are shown beneath the owner field, with one thread ID displayed on each line. You can open a Process Window for these waiting threads by diving or selecting on its number.

If TotalView cannot obtain this information, it does not show waiting thread system TIDs.

Address

This field contains the memory address of the mutex. You can open a Variable Window containing a view of the mutex’s data by diving on this field.