Introduction -to threads and processes

diff -r ebc84c812384 -r 46218c8b8afa Symbian3/PDK/Source/GUID-21A43565-FC69-553E-9617-4832AB776004.dita --- a/Symbian3/PDK/Source/GUID-21A43565-FC69-553E-9617-4832AB776004.dita Thu Mar 11 15:24:26 2010 +0000 +++ b/Symbian3/PDK/Source/GUID-21A43565-FC69-553E-9617-4832AB776004.dita Thu Mar 11 18:02:22 2010 +0000 @@ -1,57 +1,57 @@ - - - - - -Introduction -to threads and processes -

Programs consist of a number of processes, each of which contains one or -more conceptually concurrent threads of execution.

A thread is the unit of execution within a process. Every time a process -is initialised, a primary thread is created. For many applications the primary -thread is the only one that the application requires; however, processes can -create additional threads.

Each user process has its own private address space, i.e. a collection -of memory regions which that process can access. A user process cannot directly -address memory areas in the address space of another process. There is also -a special process, the Kernel process, whose threads run at supervisor privilege -level. This process normally contains two threads:

the Kernel server thread, -which is the initial thread whose execution begins at the reset vector, and -which is used to implement all Kernel functions requiring allocation or deallocation -on the Kernel heap. This is the highest priority thread in the system.
the null thread, which -runs only when no other threads are ready to run. The null thread places the -processor into idle mode to save power.

Threads execute individually and are unaware of other threads in a process. -The scheduling of threads is pre-emptive, i.e. a currently executing thread -may be suspended at any time to allow another thread to run.

Each thread is assigned a priority; at any time, the thread running is -the highest priority thread which is ready to run. Threads with equal priority -are time-sliced on a round-robin basis. Context switching between threads -involves saving and restoring the state of threads. This state includes not -only the processor registers (the thread context) but also the address space -accessible to the thread (the process context). The process context only needs -switching if a reschedule is between threads in different processes.

Compare this with active objects which allow non pre-emptive multi-tasking -within a single thread.

A thread can suspend, resume, panic and kill another thread.

When a thread is created it is put into a suspended state, it does not -begin to run until that thread’s Resume() member function -is called.

When a thread is created, it is given the priority EPriorityNormal by -default. The fact that a thread is initially put into a suspended state means -that the thread priority can be changed (RThread::SetPriority()) before the -thread is started (RThread::Resume()).

-Use -Of Shared Memory Between Threads + + + + + +Introduction +to threads and processes +

Programs consist of a number of processes, each of which contains one or +more conceptually concurrent threads of execution.

A thread is the unit of execution within a process. Every time a process +is initialised, a primary thread is created. For many applications the primary +thread is the only one that the application requires; however, processes can +create additional threads.

Each user process has its own private address space, i.e. a collection +of memory regions which that process can access. A user process cannot directly +address memory areas in the address space of another process. There is also +a special process, the Kernel process, whose threads run at supervisor privilege +level. This process normally contains two threads:

the Kernel server thread, +which is the initial thread whose execution begins at the reset vector, and +which is used to implement all Kernel functions requiring allocation or deallocation +on the Kernel heap. This is the highest priority thread in the system.
the null thread, which +runs only when no other threads are ready to run. The null thread places the +processor into idle mode to save power.

Threads execute individually and are unaware of other threads in a process. +The scheduling of threads is pre-emptive, i.e. a currently executing thread +may be suspended at any time to allow another thread to run.

Each thread is assigned a priority; at any time, the thread running is +the highest priority thread which is ready to run. Threads with equal priority +are time-sliced on a round-robin basis. Context switching between threads +involves saving and restoring the state of threads. This state includes not +only the processor registers (the thread context) but also the address space +accessible to the thread (the process context). The process context only needs +switching if a reschedule is between threads in different processes.

Compare this with active objects which allow non pre-emptive multi-tasking +within a single thread.

A thread can suspend, resume, panic and kill another thread.

When a thread is created it is put into a suspended state, it does not +begin to run until that thread’s Resume() member function +is called.

When a thread is created, it is given the priority EPriorityNormal by +default. The fact that a thread is initially put into a suspended state means +that the thread priority can be changed (RThread::SetPriority()) before the +thread is started (RThread::Resume()).

+Use +Of Shared Memory Between Threads

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