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NAME
ost::Thread - Every thread of execution in an application is created by instantiating an object of a
class derived from the Thread class.
SYNOPSIS
#include <thread.h>
Inherited by ost::PosixThread, ost::SerialService, ost::SocketService, ost::TCPSession, ost::ThreadQueue,
ost::TTYSession, and ost::UnixSession.
Public Types
enum Throw { throwNothing, throwObject, throwException }
How to raise error.
enum Cancel { cancelInitial =0, cancelDeferred =1, cancelImmediate, cancelDisabled, cancelManual,
cancelDefault =cancelDeferred }
How work cancellation.
enum Suspend { suspendEnable, suspendDisable }
How work suspend.
typedef enum ost::Thread::Throw Throw
How to raise error.
typedef enum ost::Thread::Cancel Cancel
How work cancellation.
typedef enum ost::Thread::Suspend Suspend
How work suspend.
Public Member Functions
Thread (bool isMain)
This is actually a special constructor that is used to create a thread 'object' for the current
execution context when that context is not created via an instance of a derived Thread object itself.
Thread (int pri=0, size_t stack=0)
When a thread object is contructed, a new thread of execution context is created.
Thread (const Thread &th)
A thread of execution can also be specified by cloning an existing thread.
virtual ~Thread ()
The thread destructor should clear up any resources that have been allocated by the thread.
int start (Semaphore *start=0)
When a new thread is created, it does not begin immediate execution.
int detach (Semaphore *start=0)
Start a new thread as 'detached'.
Thread * getParent (void)
Gets the pointer to the Thread class which created the current thread object.
void suspend (void)
Suspends execution of the selected thread.
void resume (void)
Resumes execution of the selected thread.
Cancel getCancel (void)
Used to retrieve the cancellation mode in effect for the selected thread.
bool isRunning (void) const
Verifies if the thread is still running or has already been terminated but not yet deleted.
bool isDetached (void) const
Check if this thread is detached.
void join (void)
Blocking call which unlocks when thread terminates.
bool isThread (void) const
Tests to see if the current execution context is the same as the specified thread object.
cctid_t getId (void) const
Get system thread numeric identifier.
const char * getName (void) const
Get the name string for this thread, to use in debug messages.
Static Public Member Functions
static Thread * get (void)
static void setStack (size_t size=0)
Set base stack limit before manual stack sizes have effect.
static void sleep (timeout_t msec)
A thread-safe sleep call.
static void yield (void)
Yields the current thread's CPU time slice to allow another thread to begin immediate execution.
static Throw getException (void)
Get exception mode of the current thread.
static void setException (Throw mode)
Set exception mode of the current thread.
static Cancel enterCancel (void)
This is used to help build wrapper functions in libraries around system calls that should behave as
cancellation points but don't.
static void exitCancel (Cancel cancel)
This is used to restore a cancel block.
Protected Member Functions
void setName (const char *text)
Set the name of the current thread.
virtual void run (void)=0
All threads execute by deriving the Run method of Thread.
virtual void final (void)
A thread that is self terminating, either by invoking exit() or leaving it's run(), will have this
method called.
virtual void initial (void)
The initial method is called by a newly created thread when it starts execution.
virtual void * getExtended (void)
Since getParent() and getThread() only refer to an object of the Thread 'base' type, this virtual
method can be replaced in a derived class with something that returns data specific to the derived
class that can still be accessed through the pointer returned by getParent() and getThread().
virtual void notify (Thread *)
When a thread terminates, it now sends a notification message to the parent thread which created it.
void exit (void)
Used to properly exit from a Thread derived run() or initial() method.
void sync (void)
Used to wait for a join or cancel, in place of explicit exit.
bool testCancel (void)
test a cancellation point for deferred thread cancellation.
void setCancel (Cancel mode)
Sets thread cancellation mode.
void setSuspend (Suspend mode)
Sets the thread's ability to be suspended from execution.
void terminate (void)
Used by another thread to terminate the current thread.
void clrParent (void)
clear parent thread relationship.
Friends
class PosixThread
class DummyThread
class Cancellation
class postream_type
class Slog
class ThreadImpl
void operator++ (Thread &th)
Signal the semaphore that the specified thread is waiting for before beginning execution.
void operator-- (Thread &th)
Detailed Description
Every thread of execution in an application is created by instantiating an object of a class derived from
the Thread class.
Classes derived from Thread must implement the run() method, which specifies the code of the thread. The
base Thread class supports encapsulation of the generic threading methods implemented on various target
operating systems. This includes the ability to start and stop threads in a synchronized and controllable
manner, the ability to specify thread execution priority, and thread specific 'system call' wrappers,
such as for sleep and yield. A thread exception is thrown if the thread cannot be created. Threading was
the first part of Common C++ I wrote, back when it was still the APE library. My goal for Common C++
threading has been to make threading as natural and easy to use in C++ application development as
threading is in Java. With this said, one does not need to use threading at all to take advantage of
Common C++. However, all Common C++ classes are designed at least to be thread-aware/thread-safe as
appropriate and necessary.
Common C++ threading is currently built either from the Posix 'pthread' library or using the win32 SDK.
In that the Posix 'pthread' draft has gone through many revisions, and many system implementations are
only marginally compliant, and even then usually in different ways, I wrote a large series of autoconf
macros found in ost_pthread.m4 which handle the task of identifying which pthread features and
capabilities your target platform supports. In the process I learned much about what autoconf can and
cannot do for you..
Currently the GNU Portable Thread library (GNU pth) is not directly supported in Common C++. While GNU
'Pth' doesn't offer direct native threading support or benefit from SMP hardware, many of the design
advantages of threading can be gained from it's use, and the Pth pthread 'emulation' library should be
usable with Common C++. In the future, Common C++ will directly support Pth, as well as OS/2 and BeOS
native threading API's.
Common C++ itself defines a fairly 'neutral' threading model that is not tied to any specific API such as
pthread, win32, etc. This neutral thread model is contained in a series of classes which handle threading
and synchronization and which may be used together to build reliable threaded applications.
Common C++ defines application specific threads as objects which are derived from the Common C++ 'Thread'
base class. At minimum the 'Run' method must be implemented, and this method essentially is the 'thread',
for it is executed within the execution context of the thread, and when the Run method terminates the
thread is assumed to have terminated.
Common C++ allows one to specify the running priority of a newly created thread relative to the 'parent'
thread which is the thread that is executing when the constructor is called. Since most newer C++
implementations do not allow one to call virtual constructors or virtual methods from constructors, the
thread must be 'started' after the constructor returns. This is done either by defining a 'starting'
semaphore object that one or more newly created thread objects can wait upon, or by invoking an explicit
'start' member function.
Threads can be 'suspended' and 'resumed'. As this behavior is not defined in the Posix 'pthread'
specification, it is often emulated through signals. Typically SIGUSR1 will be used for this purpose in
Common C++ applications, depending in the target platform. On Linux, since threads are indeed processes,
SIGSTP and SIGCONT can be used. On solaris, the Solaris thread library supports suspend and resume
directly.
Threads can be canceled. Not all platforms support the concept of externally cancelable threads. On those
platforms and API implementations that do not, threads are typically canceled through the action of a
signal handler.
As noted earlier, threads are considered running until the 'Run' method returns, or until a cancellation
request is made. Common C++ threads can control how they respond to cancellation, using
setCancellation(). Cancellation requests can be ignored, set to occur only when a cancellation 'point'
has been reached in the code, or occur immediately. Threads can also exit by returning from Run() or by
invoking the Exit() method.
Generally it is a good practice to initialize any resources the thread may require within the constructor
of your derived thread class, and to purge or restore any allocated resources in the destructor. In most
cases, the destructor will be executed after the thread has terminated, and hence will execute within the
context of the thread that requested a join rather than in the context of the thread that is being
terminated. Most destructors in derived thread classes should first call Terminate() to make sure the
thread has stopped running before releasing resources.
A Common C++ thread is normally canceled by deleting the thread object. The process of deletion invokes
the thread's destructor, and the destructor will then perform a 'join' against the thread using the
Terminate() function. This behavior is not always desirable since the thread may block itself from
cancellation and block the current 'delete' operation from completing. One can alternately invoke
Terminate() directly before deleting a thread object.
When a given Common C++ thread exits on it's own through it's Run() method, a 'Final' method will be
called. This Final method will be called while the thread is 'detached'. If a thread object is
constructed through a 'new' operator, it's final method can be used to 'self delete' when done, and
allows an independent thread to construct and remove itself autonomously.
A special global function, getThread(), is provided to identify the thread object that represents the
current execution context you are running under. This is sometimes needed to deliver signals to the
correct thread. Since all thread manipulation should be done through the Common C++ (base) thread class
itself, this provides the same functionality as things like 'pthread_self' for Common C++.
All Common C++ threads have an exception 'mode' which determines their behavior when an exception is
thrown by another Common C++ class. Extensions to Common C++ should respect the current exception mode
and use getException() to determine what to do when they are about to throw an object. The default
exception mode (defined in the Thread() constructor) is throwObject, which causes a pointer to an
instance of the class where the error occured to be thrown. Other exception modes are throwException,
which causes a class-specific exception class to be thrown, and throwNothing, which causes errors to be
ignored.
As an example, you could try to call the Socket class with an invalid address that the system could not
bind to. This would cause an object of type Socket * to be thrown by default, as the default exception
mode is throwObject. If you call setException(throwException) before the bad call to the Socket
constructor, an object of type SockException (the exception class for class Socket) will be thrown
instead.
To determine what exception class is thrown by a given Common C++ class when the exception mode is set to
throwException, search the source files for the class you are interested in for a class which inherits
directly or indirectly from class Exception. This is the exception class which would be thrown when the
exception mode is set to throwException.
The advantage of using throwException versus throwObject is that more information is available to the
programmer from the thrown object. All class-specific exceptions inherit from class Exception, which
provides a getString() method which can be called to get a human-readable error string.
Common C++ threads are often aggregated into other classes to provide services that are 'managed' from or
operate within the context of a thread, even within the Common C++ framework itself. A good example of
this is the TCPSession class, which essentially is a combination of a TCP client connection and a
separate thread the user can define by deriving a class with a Run() method to handle the connected
service. This aggregation logically connects the successful allocation of a given resource with the
construction of a thread to manage and perform operations for said resource.
Threads are also used in 'service pools'. In Common C++, a service pool is one or more threads that are
used to manage a set of resources. While Common C++ does not provide a direct 'pool' class, it does
provide a model for their implementation, usually by constructing an array of thread 'service' objects,
each of which can then be assigned the next new instance of a given resource in turn or algorithmically.
Threads have signal handlers associated with them. Several signal types are 'predefined' and have special
meaning. All signal handlers are defined as virtual member functions of the Thread class which are called
when a specific signal is received for a given thread. The 'SIGPIPE' event is defined as a 'Disconnect'
event since it's normally associated with a socket disconnecting or broken fifo. The Hangup() method is
associated with the SIGHUP signal. All other signals are handled through the more generic Signal().
Incidently, unlike Posix, the win32 API has no concept of signals, and certainly no means to define or
deliver signals on a per-thread basis. For this reason, no signal handling is supported or emulated in
the win32 implementation of Common C++ at this time.
In addition to TCPStream, there is a TCPSession class which combines a thread with a TCPStream object.
The assumption made by TCPSession is that one will service each TCP connection with a separate thread,
and this makes sense for systems where extended connections may be maintained and complex protocols are
being used over TCP.
Author
David Sugar dyfet@ostel.com
base class used to derive all threads of execution.
Examples
bug1.cpp, bug2.cpp, tcpservice.cpp, tcpstr1.cpp, thread1.cpp, and thread2.cpp.
Member Typedef Documentation
typedef enum ost::Thread::Cancel ost::Thread::Cancel
How work cancellation.
typedef enum ost::Thread::Suspend ost::Thread::Suspend
How work suspend.
typedef enum ost::Thread::Throw ost::Thread::Throw
How to raise error.
Member Enumeration Documentation
enum ost::Thread::Cancel
How work cancellation.
Enumerator
cancelInitial
used internally, do not use
cancelDeferred
exit thread on cancellation pointsuch as yield
cancelImmediate
exit befor cancellation
cancelDisabled
ignore cancellation
cancelManual
unimplemented (working in progress)
cancelDefault
default you should use this for compatibility instead of deferred
enum ost::Thread::Suspend
How work suspend.
Enumerator
suspendEnable
suspend enabled
suspendDisable
suspend disabled, Suspend do nothing
enum ost::Thread::Throw
How to raise error.
Enumerator
throwNothing
continue without throwing error
throwObject
throw object that cause error (throw this)
throwException
throw an object relative to error
Constructor & Destructor Documentation
ost::Thread::Thread (bool isMain)
This is actually a special constructor that is used to create a thread 'object' for the current execution
context when that context is not created via an instance of a derived Thread object itself. This
constructor does not support First.
Parameters
isMain bool used if the main 'thread' of the application.
ost::Thread::Thread (int pri = 0, size_t stack = 0)
When a thread object is contructed, a new thread of execution context is created. This constructor allows
basic properties of that context (thread priority, stack space, etc) to be defined. The starting
condition is also specified for whether the thread is to wait on a semaphore before begining execution or
wait until it's start method is called.
Parameters
pri thread base priority relative to it's parent.
stack space as needed in some implementations.
ost::Thread::Thread (const Thread & th)
A thread of execution can also be specified by cloning an existing thread. The existing thread's
properties (cancel mode, priority, etc), are also duplicated.
Parameters
th currently executing thread object to clone.
virtual ost::Thread::~Thread () [virtual]
The thread destructor should clear up any resources that have been allocated by the thread. The
desctructor of a derived thread should begin with Terminate() and is presumed to then execute within the
context of the thread causing terminaton.
Member Function Documentation
void ost::Thread::clrParent (void) [inline], [protected]
clear parent thread relationship.
int ost::Thread::detach (Semaphore * start = 0)
Start a new thread as 'detached'. This is an alternative start() method that resolves some issues with
later glibc implimentations which incorrectly impliment self-detach.
Returns
error code if execution fails.
Parameters
start optional starting semaphore to alternately use.
Examples
thread2.cpp.
static Cancel ost::Thread::enterCancel (void) [static]
This is used to help build wrapper functions in libraries around system calls that should behave as
cancellation points but don't.
Returns
saved cancel type.
void ost::Thread::exit (void) [protected]
Used to properly exit from a Thread derived run() or initial() method. Terminates execution of the
current thread and calls the derived classes final() method.
static void ost::Thread::exitCancel (Cancel cancel) [static]
This is used to restore a cancel block.
Parameters
cancel type that was saved.
virtual void ost::Thread::final (void) [protected], [virtual]
A thread that is self terminating, either by invoking exit() or leaving it's run(), will have this method
called. It can be used to self delete the current object assuming the object was created with new on the
heap rather than stack local, hence one may often see final defined as 'delete this' in a derived thread
class. A final method, while running, cannot be terminated or cancelled by another thread. Final is
called for all cancellation type (even immediate).
You can safe delete thread ('delete this') class on final, but you should exit ASAP (or do not try to
call CommonC++ methods...)
Note
A thread cannot delete its own context or join itself. To make a thread that is a self running object
that self-deletes, one has to detach the thread by using detach() instead of start().
See also
exit
run
Reimplemented in ost::ThreadQueue.
static Thread* ost::Thread::get (void) [static]
Referenced by ost::getThread().
Cancel ost::Thread::getCancel (void) [inline]
Used to retrieve the cancellation mode in effect for the selected thread.
Returns
cancellation mode constant.
static Throw ost::Thread::getException (void) [static]
Get exception mode of the current thread.
Returns
exception mode.
virtual void* ost::Thread::getExtended (void) [protected], [virtual]
Since getParent() and getThread() only refer to an object of the Thread 'base' type, this virtual method
can be replaced in a derived class with something that returns data specific to the derived class that
can still be accessed through the pointer returned by getParent() and getThread().
Returns
pointer to derived class specific data.
cctid_t ost::Thread::getId (void) const
Get system thread numeric identifier.
Returns
numeric identifier of this thread.
const char* ost::Thread::getName (void) const [inline]
Get the name string for this thread, to use in debug messages.
Returns
debug name.
Thread* ost::Thread::getParent (void) [inline]
Gets the pointer to the Thread class which created the current thread object.
Returns
a Thread *, or '(Thread *)this' if no parent.
virtual void ost::Thread::initial (void) [protected], [virtual]
The initial method is called by a newly created thread when it starts execution. This method is ran with
deferred cancellation disabled by default. The Initial method is given a separate handler so that it can
create temporary objects on it's own stack frame, rather than having objects created on run() that are
only needed by startup and yet continue to consume stack space.
See also
run
final
Reimplemented in ost::UnixSession, and ost::TCPSession.
bool ost::Thread::isDetached (void) const
Check if this thread is detached.
Returns
true if the thread is detached.
bool ost::Thread::isRunning (void) const
Verifies if the thread is still running or has already been terminated but not yet deleted.
Returns
true if the thread is still executing.
bool ost::Thread::isThread (void) const
Tests to see if the current execution context is the same as the specified thread object.
Returns
true if the current context is this object.
void ost::Thread::join (void)
Blocking call which unlocks when thread terminates.
virtual void ost::Thread::notify (Thread *) [protected], [virtual]
When a thread terminates, it now sends a notification message to the parent thread which created it. The
actual use of this notification is left to be defined in a derived class.
Parameters
- the thread that has terminated.
void ost::Thread::resume (void)
Resumes execution of the selected thread.
virtual void ost::Thread::run (void) [protected], [pure virtual]
All threads execute by deriving the Run method of Thread. This method is called after Initial to begin
normal operation of the thread. If the method terminates, then the thread will also terminate after
notifying it's parent and calling it's Final() method.
See also
#Initial
void ost::Thread::setCancel (Cancel mode) [protected]
Sets thread cancellation mode. Threads can either be set immune to termination (cancelDisabled), can be
set to terminate when reaching specific 'thread cancellation points' (cancelDeferred) or immediately when
Terminate is requested (cancelImmediate).
Parameters
mode for cancellation of the current thread.
static void ost::Thread::setException (Throw mode) [static]
Set exception mode of the current thread.
Returns
exception mode.
void ost::Thread::setName (const char * text) [protected]
Set the name of the current thread. If the name is passed as NULL, then the default name is set (usually
object pointer).
Parameters
text name to use.
static void ost::Thread::setStack (size_t size = 0) [inline], [static]
Set base stack limit before manual stack sizes have effect.
Parameters
size stack size to set, or use 0 to clear autostack.
void ost::Thread::setSuspend (Suspend mode) [protected]
Sets the thread's ability to be suspended from execution. The thread may either have suspend enabled
(suspendEnable) or disabled (suspendDisable).
Parameters
mode for suspend.
static void ost::Thread::sleep (timeout_t msec) [static]
A thread-safe sleep call. On most Posix systems, 'sleep()' is implimented with SIGALRM making it unusable
from multipe threads. Pthread libraries often define an alternate 'sleep' handler such as usleep(),
nanosleep(), or nap(), that is thread safe, and also offers a higher timer resolution.
Parameters
msec timeout in milliseconds.
Examples
thread1.cpp.
int ost::Thread::start (Semaphore * start = 0)
When a new thread is created, it does not begin immediate execution. This is because the derived class
virtual tables are not properly loaded at the time the C++ object is created within the constructor
itself, at least in some compiler/system combinations. The thread can either be told to wait for an
external semaphore, or it can be started directly after the constructor completes by calling the start()
method.
Returns
error code if execution fails.
Parameters
start optional starting semaphore to alternately use.
void ost::Thread::suspend (void)
Suspends execution of the selected thread. Pthreads do not normally support suspendable threads, so the
behavior is simulated with signals. On systems such as Linux that define threads as processes, SIGSTOP
and SIGCONT may be used.
void ost::Thread::sync (void) [protected]
Used to wait for a join or cancel, in place of explicit exit.
void ost::Thread::terminate (void) [protected]
Used by another thread to terminate the current thread. Termination actually occurs based on the current
setCancel() mode. When the current thread does terminate, control is returned to the requesting thread.
terminate() should always be called at the start of any destructor of a class derived from Thread to
assure the remaining part of the destructor is called without the thread still executing.
bool ost::Thread::testCancel (void) [protected]
test a cancellation point for deferred thread cancellation.
static void ost::Thread::yield (void) [static]
Yields the current thread's CPU time slice to allow another thread to begin immediate execution.
Friends And Related Function Documentation
friend class Cancellation [friend]
friend class DummyThread [friend]
void operator++ (Thread & th) [friend]
Signal the semaphore that the specified thread is waiting for before beginning execution.
Parameters
th specified thread.
void operator-- (Thread & th) [friend]
friend class PosixThread [friend]
friend class postream_type [friend]
friend class Slog [friend]
friend class ThreadImpl [friend]
Author
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