Synchronization in Software

Drawing Denso QR Bar Code in Software Synchronization
10
Generate QR In Visual C#.NET
Using Barcode generation for .NET Control to generate, create QR Code 2d barcode image in .NET applications.
Synchronization
QR Maker In Visual Studio .NET
Using Barcode maker for ASP.NET Control to generate, create Quick Response Code image in ASP.NET applications.
Event
Creating QR Code In .NET Framework
Using Barcode maker for .NET framework Control to generate, create QR Code ISO/IEC18004 image in Visual Studio .NET applications.
The event is a kernel mode primitive accessible in user mode via an opaque handle An event is a synchronization object that can take on one of two states: signaled or nonsignaled When an event goes from the non-signaled state to the signaled state (indicating that a particular event has occurred), a thread waiting on that event object will be woken up and allowed to continue execution Event objects are very commonly used to synchronize code flow execution between multiple threads For example, the Win32 API ReadFile can read data asynchronously by passing in a pointer to an OVERLAPPED structure Figure 101 illustrates the flow of events
Quick Response Code Creator In VB.NET
Using Barcode creator for Visual Studio .NET Control to generate, create QR Code image in .NET applications.
THREAD 1 CreateEvent THREAD 2
Painting Bar Code In .NET Framework
Using Barcode printer for ASP.NET Control to generate, create bar code image in ASP.NET applications.
ReadFile( , ,hEvent)
Read Bar Code In Java
Using Barcode decoder for Java Control to read, scan read, scan image in Java applications.
Read operation executes in the background
Make Data Matrix In Visual Studio .NET
Using Barcode creator for VS .NET Control to generate, create Data Matrix 2d barcode image in Visual Studio .NET applications.
Do other work
Barcode Encoder In Visual Studio .NET
Using Barcode maker for VS .NET Control to generate, create bar code image in Visual Studio .NET applications.
WaitForSingleObject(hEvent)
USS Code 128 Creation In Visual Basic .NET
Using Barcode generator for Visual Studio .NET Control to generate, create Code 128A image in VS .NET applications.
Read operation competes, SetEvent(hEvent) Execution Resume
Generate Code 128B In Java
Using Barcode creator for Java Control to generate, create Code 128B image in Java applications.
Figure 101 Part of the OVERLAPPED structure is a handle to an event that the caller passes in Because the presence of the OVERLAPPED parameter indicates that it is an asynchronous operation, ReadFile returns to the caller immediately and processes the
ECC200 Generator In C#.NET
Using Barcode creation for VS .NET Control to generate, create Data Matrix image in .NET applications.
Synchronization Basics
Bar Code Reader In VS .NET
Using Barcode recognizer for VS .NET Control to read, scan read, scan image in VS .NET applications.
read operation in the background The caller is then free to do other work When the caller is ready for the results of the read operation, he simply waits (using the WaitForSingleObject API) for the state of the event to become signaled When the background read operations succeeds, the event is set to a signaled state, thereby waking up the calling thread, and allows execution to continue There are two forms of event objects: manual reset and auto reset The key difference between the two is what happens when the event is signaled In the case of a manual reset event, the event object remains in the signaled state until explicitly reset, thereby allowing any number of threads waiting for the event object to be released In contrast, the auto reset event only allows one waiting thread to be released before being automatically reset to the nonsignaled state If no threads are waiting, the event remains in a signaled state until the first thread tries to wait for the event In user mode, an event object is represented as an opaque handle to an underlying kernel object As such, in user mode, looking at how the handle object is laid out in memory is not possible However, an extension command exists that lets you get some information about a particular handle The extension command is called !handle To see how the !handle extension command works, attach the debugger to an instance of notepadexe and issue the !handle command Listing 101 shows the abbreviated output of the !handle extension command (Note that the output might look different, depending on the state Notepad was in when you issued the command) Listing 101
Code 39 Extended Scanner In Visual Studio .NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in VS .NET applications.
0:001> Handle Type Handle Type Handle Type Handle Type Handle Type Handle Type Handle Type Handle Type !handle 74 File 3c8 Section 3cc Mutant 3d8 Mutant 3dc Mutant 3e0 Mutant 3e4 Mutant 3e8 Mutant
Drawing UPC-A Supplement 5 In Java
Using Barcode maker for Java Control to generate, create UPC Code image in Java applications.
10 SYNCHRONIZATION
Decoding DataMatrix In .NET
Using Barcode recognizer for Visual Studio .NET Control to read, scan read, scan image in VS .NET applications.
(continues)
Reading Code 128C In .NET
Using Barcode decoder for .NET Control to read, scan read, scan image in .NET applications.
10
Barcode Generator In Visual Basic .NET
Using Barcode printer for VS .NET Control to generate, create bar code image in .NET framework applications.
Synchronization
Printing Data Matrix ECC200 In Java
Using Barcode drawer for Java Control to generate, create ECC200 image in Java applications.
Listing 101
European Article Number 13 Recognizer In .NET Framework
Using Barcode decoder for .NET Control to read, scan read, scan image in Visual Studio .NET applications.
(continued)
Generate UPC - 13 In Java
Using Barcode generator for Java Control to generate, create EAN13 image in Java applications.
Handle 3f0 Type Handle 42c Type Handle 438 Type Handle 43c Type Handle 47c Type 37 Handles Type None Event Section File Port Directory Mutant WindowStation Semaphore Key Desktop Section Key Section Port Event
Count 1 5 4 4 2 3 6 2 5 4 1
As you can see, the !handle extension command (without parameters) dumps out all the handles opened in the process with abbreviated information To get more detailed information on a particular handle, you add the handle value to the !handle extension command followed by a value that represents the depth of the information to be displayed Using a value of f gives you the most exhaustive information Let s use handle 47c (an event) as an example (see Listing 102) Listing 102
0:001> !handle 47c f Handle 614 Type Event Attributes 0
Synchronization Basics
GrantedAccess 0x1f0003: Delete,ReadControl,WriteDac,WriteOwner,Synch QueryState,ModifyState HandleCount 2 PointerCount 4 Name <none> Object Specific Information Event Type Auto Reset Event is Set