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GMonitor Class Reference

#include <GThreads.h>

Inheritance diagram for GMonitor:

GSafeFlags

List of all members.


Detailed Description

Monitor class. Monitors have been first described in (C.A.R Hoare, Communications of the ACM, 17(10), 1974). This mechanism provides the basic mutual exclusion (mutex) and thread notification facilities (condition variables).

Only one thread can own the monitor at a given time. Functions {enter} and {leave} can be used to acquire and release the monitor. This mutual exclusion provides an efficient way to protect segment of codes ({critical sections}) which should not be simultaneously executed by two threads. Class {GMonitorLock} provides a convenient way to do this effectively.

When the thread owning the monitor calls function {wait}, the monitor is released and the thread starts waiting until another thread calls function {signal} or {broadcast}. When the thread wakes-up, it re-acquires the monitor and function wait# returns. Since the signaling thread must acquire the monitor before calling functions signal# and broadcast#, the signaled thread will not be able to re-acquire the monitor until the signaling thread(s) releases the monitor.

{ Note} --- Both the copy constructor and the copy operator are declared as private members. It is therefore not possible to make multiple copies of instances of this class, as implied by the class semantic.

Definition at line 362 of file GThreads.h.


Public Member Functions

GThreads.h
Files #"GThreads.h"# and #"GThreads.cpp"# implement common entry points for multithreading on multiple platforms. Each execution thread is represented by an instance of class {GThread}. Synchronization is provided by class {GMonitor} which implements a monitor (C.A.R Hoare, Communications of the ACM, 17(10), 1974).

The value of compiler symbol THREADMODEL# selects an appropriate implementation for these classes. The current implementation supports the following values: {description} [-DTHREADMODEL=NOTHREADS] Dummy implementation. This is a good choice when the multithreading features are not required, because it minimizes the portability problems. This is currently the default when compiling under Unix. [-DTHREADMODEL=WINTHREADS] Windows implementation. This is the default when compiling under Windows. [-DTHREADMODEL=MACTHREADS] Macintosh implementation, which is based on the MacOS cooperative model. The current implementation does not yet fully support synchronization. This is the default when compiling under MacOS. [-DTHREADMODEL=POSIXTHREADS] Posix implementation. This implementation also supports DCE threads. The behavior of the code is subject to the quality of the system implementation of Posix threads. [-DTHREADMODEL=COTHREADS] Custom cooperative threads. These custom threads do not redefine system calls. Before executing a potentially blocking system function, each thread must explicitly check whether it is going to block and yield control explicitly if this is the case. This code must be compiled with a patched version of egcs-1.1.1 {http://egcs.cygnus.com}. The patch addresses exception thread-safety and is provided in #"@Tools/libgcc2.c.diff"#. Once you get the right compiler, this implementation is remarkably compact and portable. A variety of processors are supported, including mips, intel, sparc, hppa, and alpha. [-DTHREADMODEL=JRITHREADS] Java implementation hooks. Multi-threading within a Netscape plugin can be tricky. A simple idea however consists of implementing the threading primitives in Java and to access them using JRI. The classes just contain a JRIGlobalRef. This is not a real implementation since everything (Java code, native functions, stubs, exception thread safety) must be addressed by the plugin source code. Performance may be a serious issue. {description}

{ Portability}: The simultaneous use of threads and exceptions caused a lot of portability headaches under Unix. We eventually decided to implement the COTHREADS cooperative threads (because preemptive threads have more problems) and to patch EGCS in order to make exception handling COTHREAD-safe.

Portable threads

Author:
L\'eon Bottou <leonb@research.att.com> -- initial implementation.\ Praveen Guduru <praveen@sanskrit.lz.att.com> -- mac implementation.
From: Leon Bottou, 1/31/2002 Almost unchanged by Lizardtech. GSafeFlags should go because it not as safe as it claims.

Version:
#
Id
GThreads.h,v 1.10 2003/11/07 22:08:21 leonb Exp
#

void broadcast ()
void enter ()
 GMonitor ()
void leave ()
void signal ()
void wait (unsigned long timeout)
void wait ()
 ~GMonitor ()

Private Member Functions

 GMonitor (const GMonitor &)
GMonitoroperator= (const GMonitor &)

The documentation for this class was generated from the following file:

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