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Depends on D137611 Differential Revision: https://phabricator.services.mozilla.com/D137612
63 lines
2.5 KiB
ReStructuredText
63 lines
2.5 KiB
ReStructuredText
In addition to the mutex type :ref:`PRLock`, NSPR provides a special type,
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:ref:`PRMonitor`, for use in Java programming. This chapter describes the
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NSPR API for creation and manipulation of a mutex of type :ref:`PRMonitor`.
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- `Monitor Type <#Monitor_Type>`__
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- `Monitor Functions <#Monitor_Functions>`__
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With a mutex of type :ref:`PRLock`, a single thread may enter the monitor
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only once before it exits, and the mutex can have multiple associated
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condition variables.
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With a mutex of type :ref:`PRMonitor`, a single thread may re-enter a
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monitor as many times as it sees fit. The first time the thread enters a
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monitor, it acquires the monitor's lock and the thread's entry count is
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incremented to 1. Each subsequent time the thread successfully enters
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the same monitor, the thread's entry count is incremented again, and
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each time the thread exits the monitor, the thread's entry count is
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decremented. When the entry count for a thread reaches zero, the thread
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releases the monitor's lock, and other threads that were blocked while
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trying to enter the monitor will be rescheduled.
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A call to :ref:`PR_Wait` temporarily returns the entry count to zero. When
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the calling thread resumes, it has the same entry count it had before
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the wait operation.
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Unlike a mutex of type :ref:`PRLock`, a mutex of type :ref:`PRMonitor` has a
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single, implicitly associated condition variable that may be used to
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facilitate synchronization of threads with the change in state of
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monitored data.
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For an introduction to NSPR thread synchronization, including locks and
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condition variables, see `Introduction to
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NSPR <Introduction_to_NSPR>`__.
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.. _Monitor_Type:
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Monitor Type
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------------
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With the exception of :ref:`PR_NewMonitor`, which creates a new monitor
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object, all monitor functions require a pointer to an opaque object of
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type :ref:`PRMonitor`.
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.. _Monitor_Functions:
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Monitor Functions
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-----------------
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All monitor functions are thread-safe. However, this safety does not
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extend to protecting the monitor object from deletion.
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- :ref:`PR_NewMonitor` creates a new monitor.
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- :ref:`PR_DestroyMonitor` destroys a monitor object.
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- :ref:`PR_EnterMonitor` enters the lock associated with a specified
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monitor.
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- :ref:`PR_ExitMonitor` decrements the entry count associated with a
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specified monitor.
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- :ref:`PR_Wait` waits for a notify on a specified monitor's condition
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variable.
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- :ref:`PR_Notify` notifies a thread waiting on a specified monitor's
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condition variable.
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- :ref:`PR_NotifyAll` notifies all threads waiting on a specified
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monitor's condition variable.
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