Transcript Lecture 2 on Windows CE files and processes

Operating systems
Windows CE files.
Windows CE databases.
Windows CE processes.
© 2004 Wayne Wolf
Overheads for Computers as
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WinCE file system
Designed for devices without rotating
storage.
May use disk drives.
Based upon object store.
Object store is undocumented---can’t
determine format in memory.
API is fairly complete version of Win32 file
system.
© 2004 Wayne Wolf
Overheads for Computers as
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Object store
Default file system in WinCE.
Stores files in compressed form.
Applications cannot easily distinguish
between RAM and ROM files.
Limited to 256 MB of RAM.
Individual file limited to 32 MB.
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Other WinCE file systems
Installable file system (IFS): up to 256 storage
devices with file systems.
Every storage device is a directory from root.
Doesn’t use drive letters C: etc.
Doesn’t have size limitations of object store.
Uses Windows-style file names.
Supports many attribute flags: read-only,
system, hidden, etc.
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Memory-mapped files
Can use memory reads/writes to read and
write file.
Don’t need FileRead(), FileWrite().
Opened with specialized calls
CreateFileForMapping(),
CreateFileMapping().
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Overheads for Computers as
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WinCE registry
Database that stores data on configuration of
WinCE and applications.
Used to store data that needs to be saved.
Contains keys, values.
Multiple levels of keys separated by ‘\’.
Registry access:
Key containing value is opened.
Value read or written.
Key is closed.
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WinCE databases
Designed for address lists, etc.
Provides basic database functions:
One level.
At most four sort indexes.
Not supported by other Windows
platforms.
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Database records
 Database: set of records.
 Record: unlimited number of properties.
 Property types:
2-byte signed integer.
2-byte unsigned integer.
4-byte signed integer.
4-byte unsigned integer.
Time/date structure.
Null-terminated Unicode string.
Collection of bytes.
Boolean.
8-byte signed value.
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Database volumes
Volume: format for storing database in a
file.
Can be stored in compact flash, etc.
Must be mounted and dismounted.
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Windows CE modules and
processes
Types of executable code:
Applications .exe.
Dynamically linked libraries .dll.
A process is an instance of an application.
Each process has its own thread.
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DLLs vs EXEs
An executable can be executed.
A DLL cannot be directly executed.
Must be called by an EXE or DLL.
EXE can list the DLL in its import table.
DLL can be loaded explicitly.
Share file format.
Only difference is markers in the header.
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WinCE processes
Only 32 processes can execute at any one
time.
WinCE processes contain less state than
other Windows processes.
No current directory, etc.
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WinCE startup
When started, WinCE starts four
processes:
Kernel NK.exe.
System services FileSys.exe.
GUI support GWES.exe.
Device drivers Device.exe.
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WinCE threads
A thread is a flow of control.
Has its own stack and register set.
A process has one or more threads.
Primary process for threads.
Process can create an arbitrary number of
additional threads.
All threads in a process share the same
address space.
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Threads and scheduling
The kernel schedules threads.
Preemptive scheduling.
Time sliced into quanta.
Preemptive scheduling:
Higher priority ready thread runs first.
Thread can be blocked.
Scheduler supports priority inheritance to solve
priority inversion.
256 possible scheduling priorities.
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Priorities and quanta
Priority can be changed by the thread or
by another thread.
0 is highest priority, 255 is lowest.
Each thread may have its own time
quantum.
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WinCE fibers
Fiber: thread-like object that is scheduled
by the application, not the system.
Application creates thread, then turns it into
a fiber.
Introduced for better compatibility with
Unix.
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Thread local storage
Each thread that calls a routine can have
its own local storage.
Persistent.
Unique to a thread.
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WinCE synchronization
Based on synchronization objects.
Thread waits on synchronization object.
Signal to objectd causes thread to unblock.
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WinCE events
Event object capture signals:
Named objects.
In signaled or nonsignaled state.
Event object must be created in each
process that wants to use it.
Processes can wait on objects.
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Semaphore objects
Counting semaphores.
Zero count is not signaled.
Non-zero count is signaled.
Threads can wait on semaphore objects.
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Mutexes
Used to make sure that only one process
at a time works on a resource.
Signal is on when not owned by a thread.
Signal is off when owned by a thread.
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Critical sections
Critical section of code must not be
executed at same time as another critical
section.
Controlled by EnterCriticalSection(),
LeaveCriticalSection().
© 2004 Wayne Wolf
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Components