Shared Memory
Posted: Sat Sep 29, 2012 4:43 am
Thanks to Mistrel & Siggi Rings for their code. I used it as a base to understand how to write a shared memory process. There are two programs, a producer and a consumer. The producer creates the shared memory, and the consumer is able to read it.
Switch between the two, you'll see how they work.
Question for those who may know: Can there be a possibility of IMA's if a read is done while data is being written to the shared memory? Has anyone handled such a situation?
Rich
Code: Select all
; shm_producer.pb
EnableExplicit
Procedure.i CreateMap(*MapName, Size.i)
Protected hFileMap.i
Protected *MapView.i
Protected Security.SECURITY_ATTRIBUTES
hFileMap = CreateFileMapping_(-1, 0, #PAGE_READWRITE, 0, Size, *MapName)
ProcedureReturn hFileMap
EndProcedure
Procedure.s GetMapString(*MapName)
Protected hFileMap.i
Protected *MapView
Protected Value.s
hFileMap = OpenFileMapping_(#FILE_MAP_ALL_ACCESS, 0, *MapName)
If hFileMap
*MapView = MapViewOfFile_(hFileMap, #FILE_MAP_WRITE, 0, 0, 0)
;/ Read the map value to the file then Unmap the mapped view of the file from memory
If *MapView
Value = PeekS(*MapView)
UnmapViewOfFile_(*MapView)
Else
Value = ""
EndIf
CloseHandle_(hFileMap)
Else
Value = ""
EndIf
ProcedureReturn Value
EndProcedure
Procedure.i SetMapString(*MapName, *Value)
Protected hFileMap.i
Protected *MapView
Protected Value.s = PeekS(*Value)
Protected retValue.i = #False
hFileMap = OpenFileMapping_(#FILE_MAP_ALL_ACCESS, 0, *MapName)
If hFileMap
*MapView = MapViewOfFile_(hFileMap, #FILE_MAP_WRITE, 0, 0, 0)
;/ Write the map value to the file, then Unmap the mapped view of the file from memory
If *MapView
PokeS(*MapView, Value)
UnmapViewOfFile_(*MapView)
retValue = #True
EndIf
CloseHandle_(hFileMap)
EndIf
ProcedureReturn retValue
EndProcedure
Procedure.i CloseMapPtr(*MapPtr)
Protected Value.i
;/ Unmap the mapped view of the file from memory
If UnmapViewOfFile_(*MapPtr)
Value = #True
Else
Value = #False
EndIf
ProcedureReturn Value
EndProcedure
Procedure CloseMap(hMap)
Protected Value.i
If CloseHandle_(hMap)
Value = #True
Else
Value = #False
EndIf
ProcedureReturn Value
EndProcedure
Define hMap.i
Define *MapView
Define MapName.s = "SharedMapName"
Define sendStr.s = ""
Define mapSize.i = 512
hMap = CreateMap(@MapName, mapSize)
;/ Output from source
OpenConsole()
sendStr = "First string to be sent..., start consumer process"
SetMapString(@MapName, @sendStr)
PrintN("Set Map = " + GetMapString(@MapName))
Repeat
PrintN("")
Print("Enter text To send, or press <enter> to quit: ")
sendStr = Input()
If sendStr <> ""
SetMapString(@MapName, @sendStr)
PrintN("Set Map = " + GetMapString(@MapName))
Else
Break
EndIf
ForEver
CloseMapPtr(*MapView)
CloseMap(hMap)
CloseConsole()
EndCode: Select all
; shm_consumer.pb
EnableExplicit
Procedure.i GetMapPtr(*MapName)
Protected hFileMap.i
Protected *MapView
Protected Value.i = #False
hFileMap = OpenFileMapping_(#FILE_MAP_ALL_ACCESS, 0, *MapName)
If hFileMap
*MapView = MapViewOfFile_(hFileMap, #FILE_MAP_WRITE, 0, 0, 0)
If *MapView
Value = *MapView
EndIf
CloseHandle_(hFileMap)
EndIf
ProcedureReturn Value
EndProcedure
Define *MapView
Define MapName.s = "SharedMapName"
Define sentText.s = ""
;/ Output from source
OpenConsole()
;/ Output from other process
Repeat
*MapView = GetMapPtr(@MapName)
If *MapView > 0
sentText = PeekS(*MapView)
If sentText <> ""
PrintN("Read Map = " + sentText)
PrintN("")
PrintN("Press <enter> to check shared memory")
Input()
Else
Break
EndIf
Else
Break
EndIf
ForEver
CloseConsole()
EndQuestion for those who may know: Can there be a possibility of IMA's if a read is done while data is being written to the shared memory? Has anyone handled such a situation?
Rich
