Monitors

NSPR
About NSPR
NSPR API Reference
NSPR Build Instruction
NSPR Release Process
Introduction to NSPR
NSPR Types
Threads
1. Threading Types and Constants
2. Threading Functions
Process Initialization
Locks
1. Lock Type
2. Lock Functions
Condition Variables
1. Condition Variable Type
2. Condition Variable Functions
Monitors
1. Monitor Type
2. Monitor Functions
Cached Monitors
1. Cached Monitor Functions
I/O Types
I/O Functions
Network Addresses
1. Network Address Types and Constants
2. Network Address Functions
Atomic Operations
Interval Timing
1. Interval Time Type and Constants
2. Interval Functions
Date and Time
Memory Management Operations
1. Memory Allocation Functions
2. Memory Allocation Macros
String Operations
Floating Point Number to String Conversion
Linked Lists
1. Linked List Types
  1. PRCList
2. Linked List Macros
Dynamic Library Linking
Process Management and Interprocess Communication
1. Process Management Types and Constants
  1. PRProcess
  2. PRProcessAttr
2. Process Management Functions
  1. Setting the Attributes of a New Process
  2. Creating and Managing Processes
Logging
Named Shared Memory
1. Shared Memory Protocol
2. Named Shared Memory Functions
Anonymous Shared Memory
1. Anonymous Memory Protocol
2. Anonymous Shared Memory Functions
IPC Semaphores
1. IPC Semaphore Functions
Thread Pools
1. Thread Pool Types
2. Thread Pool Functions
Random Number Generator
1. Random Number Generator Function
Hash Tables
1. Hash Tables and Type Constants
2. Hash Table Functions
NSPR Error Handling
Contribute
2. The MDN Project

In addition to the mutex type PRLock, NSPR provides a special type, PRMonitor, for use in Java programming. This chapter describes the NSPR API for creation and manipulation of a mutex of type PRMonitor.

With a mutex of type PRLock, a single thread may enter the monitor only once before it exits, and the mutex can have multiple associated condition variables.

With a mutex of type PRMonitor, a single thread may re-enter a monitor as many times as it sees fit. The first time the thread enters a monitor, it acquires the monitor's lock and the thread's entry count is incremented to 1. Each subsequent time the thread successfully enters the same monitor, the thread's entry count is incremented again, and each time the thread exits the monitor, the thread's entry count is decremented. When the entry count for a thread reaches zero, the thread releases the monitor's lock, and other threads that were blocked while trying to enter the monitor will be rescheduled.

A call to PR_Wait temporarily returns the entry count to zero. When the calling thread resumes, it has the same entry count it had before the wait operation.

Unlike a mutex of type PRLock, a mutex of type PRMonitor has a single, implicitly associated condition variable that may be used to facilitate synchronization of threads with the change in state of monitored data.

For an introduction to NSPR thread synchronization, including locks and condition variables, see Introduction to NSPR.

Monitor Type

With the exception of PR_NewMonitor, which creates a new monitor object, all monitor functions require a pointer to an opaque object of type PRMonitor.

Monitor Functions

All monitor functions are thread-safe. However, this safety does not extend to protecting the monitor object from deletion.