Using vs 2003, vb.net sql msde..
Consider the following code snippets. See **** for questions. All are
shared and accessed by multiple threads simultaneiously.
' Instantiate per for this shared class
Private Shared gcCDsd As New Class_Component_Designer
Private Shared Sub tblMETHODS_DETAILSC_ADD_Row(ByVal
tblMethods_Summary_Row_Number_0_Based As Integer, ByVal Summary_Text As
String, Optional ByVal Details_Text As String = "", Optional ByVal
Exception_Thrown_Message As String = "")
****** Question 0) The same as question 2 below for the arguments above.
... code to create row to add
SyncLock (gcCDsd.DS_Methods.Methods_Details)
' Add new DataRow to DataSet
gcCDsd.DS_Methods.Methods_Details.AddMethods_Detai lsRow(DR_To_Add)
' Call method to update row to datasourse
Rows_Updated = DLsd.tblMETHODS_DETAILS_UPDATE()
End SyncLock
end sub
Private Shared Function tblMETHODS_DETAILS_UPDATE() As Integer
' Purpose: Updates the DataSource From the DataSet for this table only
****** Question 1) Since gcCDsd.DS_Methods.Methods_Details is synclocked in
the calling method, does it need to be synclocked again here. I think not,
since it would seem to be already locked. If so, it would seem that the
same thread running into the same item with a 2nd synclock on it would
ignore the 2nd synclock. Is that thinking correct?
' Holds Rows affected by DataAdapter commands, such as FILL or UPDATED
Dim Rows_Updated As Integer = -1
' call method to update datasource
Rows_Updated = DL.cmdUPDATE_DataSource(gcCDsd.DA_tblMethods_Detai ls,
gcCDsd.DS_Methods.Methods_Details)
' return rows updated
Return Rows_Updated
End Function
Friend Shared Function cmdUPDATE_DataSource(ByVal SQL_Data_Adapter As
SqlDataAdapter, ByVal DataTable_To_Update As DataTable) As Integer
' Purpose: Updates any changes made to a dataset datatable to the
datasource
****** Question 2) Do the parameters passed above need to be synclocked?
In other words, if 2 threads call this, do the arguments above instantiate a
new variable each time it is called (like dim SQL_Data_Adapter As
SqlDataAdapter would) or do they amount to shared variables that must be
protected by synclocks? It worked with out synclocks with 2 threads, but as
I have added threads I have had problems.
' Holds number of DS rows Updated to DataSource
Dim Rows_Updated As Integer = -1
****** Question 3) You would never synclock the next DIM line, since each
pass by a different thread (even at the same time) would create its own
DT_With_Changes to work with.
' create DataTable to hold only the changes in table
Dim DT_With_Changes As New DataTable
' load with rows that have changes in table
DT_With_Changes = DataTable_To_Update.GetChanges()
Rows_Updated = SQL_Data_Adapter.Update(DT_With_Changes)
' all rows for this table set back to unmodified.
DataTable_To_Update.AcceptChanges()
' Return number of rows updated6
Return Rows_Updated
End Function
Thanks!
Bob Day
10  3135  ****** Question 1) Since gcCDsd.DS_Methods.Methods_Details is synclocked
in the calling method, does it need to be synclocked again here. I think
not, since it would seem to be already locked. If so, it would seem that the
same thread running into the same item with a 2nd synclock on it would
ignore the 2nd synclock. Is that thinking correct?
You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only allows
one thread through the gate at a time.
The variable that you use in the synclock is kind of like a ticket to get
through the gate, but there is (should be) only one ticket.
The first thread to come to the synclock statement "grabs" the ticket. The
bouncer at the front gate sees he has the ticket and lets him through. The
thread then gives up the ticket at the back gate (the end of the synclock
block). The second thread must wait in line until he can get his hands on
the ticket.
I would recommend creating a seperate variable used for locking.
****** Question 2) Do the parameters passed above need to be synclocked?
In other words, if 2 threads call this, do the arguments above instantiate
a new variable each time it is called (like dim SQL_Data_Adapter As
SqlDataAdapter would) or do they amount to shared variables that must be
protected by synclocks? It worked with out synclocks with 2 threads, but
as I have added threads I have had problems.
All arguments get a seperate copy for each thread as they are placed on the
stack, and stacks are managed on a per-thread basis. However, what you have
as arguments here are object references (in essense pointers to some object
that lives on the heap). Getting multiple copies of pointers doesn't matter
because you are referencing the same objects on the heap, which might be
doing something at the time any particular thread is trying to use it.
Synclock this procudure to prevent that from happening (remember, you
synclocking code, not variables).
****** Question 3) You would never synclock the next DIM line, since each
pass by a different thread (even at the same time) would create its own
DT_With_Changes to work with.
Once again, you synclock code, not variables :-)
However, you are right in saying that locally-scoped variables get created
unique to the current thread, so you don't need to worry about them, unless
they are references to a common object on the heap. In this case not,
because each thread is creating a NEW object.
-Rob Teixeira [MVP]
With all due respect, you are giving me to question 1 the exact opposite
answer I have been previously given in this newsgroup. Previous, it was
stated that you don't sysnclock code, you synclock shared or global
varialbles, modify them, end sycnlock , since those variables can be
modified by another thread.
You are saying create an arbitrary variable, and synclock all the code you
want (whether it pertains to shared or global variables or not), not
worrying about shared or global variables, like the follwing:
Private shared sub ToSomething
dim x as string
synclock x
..all code
end synclock
End Sub
Your approach seems easier, but by the vary nature of creating an arbitrary
variable to use synclock, that does not seem how synclock was intended to be
used.
Please advise. Also, can you provide soem URLs on your approach?
Thansk!
Bob
"Rob Teixeira [MVP]" <RobTeixeira@@msn.com> wrote in message
news:uU*************@TK2MSFTNGP09.phx.gbl... ****** Question 1) Since gcCDsd.DS_Methods.Methods_Details is synclocked in the calling method, does it need to be synclocked again here. I think
not, since it would seem to be already locked. If so, it would seem that the
same thread running into the same item with a 2nd synclock on it would
ignore the 2nd synclock. Is that thinking correct?
You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only allows
one thread through the gate at a time.
The variable that you use in the synclock is kind of like a ticket to get
through the gate, but there is (should be) only one ticket.
The first thread to come to the synclock statement "grabs" the ticket. The
bouncer at the front gate sees he has the ticket and lets him through. The
thread then gives up the ticket at the back gate (the end of the synclock
block). The second thread must wait in line until he can get his hands on
the ticket.
I would recommend creating a seperate variable used for locking.
****** Question 2) Do the parameters passed above need to be
synclocked? In other words, if 2 threads call this, do the arguments above
instantiate a new variable each time it is called (like dim SQL_Data_Adapter As
SqlDataAdapter would) or do they amount to shared variables that must be
protected by synclocks? It worked with out synclocks with 2 threads,
but as I have added threads I have had problems.
All arguments get a seperate copy for each thread as they are placed on
the stack, and stacks are managed on a per-thread basis. However, what you
have as arguments here are object references (in essense pointers to some
object that lives on the heap). Getting multiple copies of pointers doesn't
matter because you are referencing the same objects on the heap, which might be
doing something at the time any particular thread is trying to use it.
Synclock this procudure to prevent that from happening (remember, you
synclocking code, not variables).
****** Question 3) You would never synclock the next DIM line, since
each pass by a different thread (even at the same time) would create its own
DT_With_Changes to work with.
Once again, you synclock code, not variables :-)
However, you are right in saying that locally-scoped variables get created
unique to the current thread, so you don't need to worry about them,
unless they are references to a common object on the heap. In this case not,
because each thread is creating a NEW object.
-Rob Teixeira [MVP]
You don't want to use a local variable as your sync mechanism.
Synclock creates a barrier around reentrant code (code that can be accessed
by multiple threads) to prevent multiple threads from executing that code at
the same time. The object you use inside the parens of the Synclock
statement is mearly used as a ticket to get into the synclocked code
barrier. Only one thread can "grab" that ticket at a time.
Most early examples used a class' Type object as this ticket, but that has
since proven to be a bad idea. You can read more about that here: http://msdn.microsoft.com/library/de...ui06032003.asp
-Rob Teixeira [MVP]
"Bob Day" <Bo****@TouchTalk.net> wrote in message
news:%2****************@TK2MSFTNGP11.phx.gbl... With all due respect, you are giving me to question 1 the exact opposite
answer I have been previously given in this newsgroup. Previous, it was
stated that you don't sysnclock code, you synclock shared or global
varialbles, modify them, end sycnlock , since those variables can be
modified by another thread.
You are saying create an arbitrary variable, and synclock all the code you
want (whether it pertains to shared or global variables or not), not
worrying about shared or global variables, like the follwing:
Private shared sub ToSomething
dim x as string
synclock x
..all code
end synclock
End Sub
Your approach seems easier, but by the vary nature of creating an
arbitrary variable to use synclock, that does not seem how synclock was intended to
be used.
Please advise. Also, can you provide soem URLs on your approach?
Thansk!
Bob
Rob, You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only allows
one thread through the gate at a time.
Are you sure about this?
Yes the SyncLock itself is around a block of code, however is not its real
intent to protect one or more 'shared' variables?
In other words why protect a block of code that does not reference 'shared'
variables?
By 'shared' variable I mean an value (reference type or value type) that can
be accessed by two threads simultaneously. Either a field declared in a
Module, in a Class with the Shared keyword, or an instance field in a Class
that the object itself is referenced by two threads.
I know what you mean by the above statement, I want to make sure that Bob
Day knows what you mean by the above statement!
Unfortunately I can't really explain it any better then I already have. (the
previous thread Bob Day mentions).
Hope this helps
Jay
"Rob Teixeira [MVP]" <RobTeixeira@@msn.com> wrote in message
news:uU*************@TK2MSFTNGP09.phx.gbl... ****** Question 1) Since gcCDsd.DS_Methods.Methods_Details is synclocked in the calling method, does it need to be synclocked again here. I think
not, since it would seem to be already locked. If so, it would seem that the
same thread running into the same item with a 2nd synclock on it would
ignore the 2nd synclock. Is that thinking correct?
You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only allows
one thread through the gate at a time.
The variable that you use in the synclock is kind of like a ticket to get
through the gate, but there is (should be) only one ticket.
The first thread to come to the synclock statement "grabs" the ticket. The
bouncer at the front gate sees he has the ticket and lets him through. The
thread then gives up the ticket at the back gate (the end of the synclock
block). The second thread must wait in line until he can get his hands on
the ticket.
I would recommend creating a seperate variable used for locking.
****** Question 2) Do the parameters passed above need to be
synclocked? In other words, if 2 threads call this, do the arguments above
instantiate a new variable each time it is called (like dim SQL_Data_Adapter As
SqlDataAdapter would) or do they amount to shared variables that must be
protected by synclocks? It worked with out synclocks with 2 threads,
but as I have added threads I have had problems.
All arguments get a seperate copy for each thread as they are placed on
the stack, and stacks are managed on a per-thread basis. However, what you
have as arguments here are object references (in essense pointers to some
object that lives on the heap). Getting multiple copies of pointers doesn't
matter because you are referencing the same objects on the heap, which might be
doing something at the time any particular thread is trying to use it.
Synclock this procudure to prevent that from happening (remember, you
synclocking code, not variables).
****** Question 3) You would never synclock the next DIM line, since
each pass by a different thread (even at the same time) would create its own
DT_With_Changes to work with.
Once again, you synclock code, not variables :-)
However, you are right in saying that locally-scoped variables get created
unique to the current thread, so you don't need to worry about them,
unless they are references to a common object on the heap. In this case not,
because each thread is creating a NEW object.
-Rob Teixeira [MVP]
In article <Oo**************@TK2MSFTNGP10.phx.gbl>, Jay B. Harlow [MVP - Outlook] wrote: Rob, You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only allows
one thread through the gate at a time. Are you sure about this?
Rob is correct, IMHO.
Yes the SyncLock itself is around a block of code, however is not its real
intent to protect one or more 'shared' variables?
It's intent is to create a critical section to protect any shared
resource. That may not necessarily be a shared/member variable.
In other words why protect a block of code that does not reference 'shared'
variables?
Two threads writing to a file... They may not share a variable, but
they may share access to the file. Its about shared resources.
--
Tom Shelton
MVP [Visual Basic]
"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in message
news:Oo**************@TK2MSFTNGP10.phx.gbl... Rob, You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only
allows one thread through the gate at a time. Are you sure about this?
Sure am :-)
Yes the SyncLock itself is around a block of code, however is not its real
intent to protect one or more 'shared' variables?
Not necessarily. Its purpose is to protect reentrant code from multiple
simultaneous threads of execution (and its quite likely that what you might
indirectly be protecting is a shared variable that should only be accessed
by one thread at a time).
In other words why protect a block of code that does not reference
'shared' variables?
It might be trying to access a system resource that shouldn't be accessed by
simultaneous threads of execution?
By 'shared' variable I mean an value (reference type or value type) that
can be accessed by two threads simultaneously. Either a field declared in a
Module, in a Class with the Shared keyword, or an instance field in a
Class that the object itself is referenced by two threads.
I know what you mean by the above statement, I want to make sure that Bob
Day knows what you mean by the above statement!
Unfortunately I can't really explain it any better then I already have.
(the previous thread Bob Day mentions).
Check out my other post to Bob.
Let's say, for example, that you have a shared object. And, you know there's
nothing wrong with accessing (reading) one of its properties regardless of
how many threads are trying to do that simultaneously. However, you don't
want simultaneous calls to this object's "ChangeCriticalStuff" method. You
don't want to lock the whole object, just the critical reenterant method.
Does that help?
Of course, there are many more variety of situations you have to account for
when dealing with multi-threading, so don't take this one example as the
only thing that needs consideration.
-Rob Teixeira [MVP]
Hope this helps
Jay
Rob,
You need to make sure it helps Bob Day!
As I totally agree with what you & Tom are saying, I'm just trying to ensure
you say it in a way that Bob Day understands!
Its is not worth my time to "split hairs" with you!
Jay
"Rob Teixeira [MVP]" <RobTeixeira@@msn.com> wrote in message
news:OB**************@tk2msftngp13.phx.gbl...
"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in message
news:Oo**************@TK2MSFTNGP10.phx.gbl... Rob, You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only allows one thread through the gate at a time. Are you sure about this?
Sure am :-)
Yes the SyncLock itself is around a block of code, however is not its
real intent to protect one or more 'shared' variables?
Not necessarily. Its purpose is to protect reentrant code from multiple
simultaneous threads of execution (and its quite likely that what you
might indirectly be protecting is a shared variable that should only be accessed
by one thread at a time).
In other words why protect a block of code that does not reference 'shared' variables?
It might be trying to access a system resource that shouldn't be accessed
by simultaneous threads of execution?
By 'shared' variable I mean an value (reference type or value type) that can be accessed by two threads simultaneously. Either a field declared in a
Module, in a Class with the Shared keyword, or an instance field in a
Class that the object itself is referenced by two threads.
I know what you mean by the above statement, I want to make sure that
Bob Day knows what you mean by the above statement!
Unfortunately I can't really explain it any better then I already have.
(the previous thread Bob Day mentions).
Check out my other post to Bob.
Let's say, for example, that you have a shared object. And, you know
there's nothing wrong with accessing (reading) one of its properties regardless of
how many threads are trying to do that simultaneously. However, you don't
want simultaneous calls to this object's "ChangeCriticalStuff" method. You
don't want to lock the whole object, just the critical reenterant method.
Does that help?
Of course, there are many more variety of situations you have to account
for when dealing with multi-threading, so don't take this one example as the
only thing that needs consideration.
-Rob Teixeira [MVP]
Hope this helps
Jay
Tom,
You need to make sure it helps Bob Day!
As I totally agree with what you & Tom are saying, I'm just trying to ensure
you say it in a way that Bob Day understands!
Its is not worth my time to "split hairs" with you!
Jay
"Tom Shelton" <to*@mtogden.com> wrote in message
news:ub**************@TK2MSFTNGP12.phx.gbl... In article <Oo**************@TK2MSFTNGP10.phx.gbl>, Jay B. Harlow [MVP -
Outlook] wrote: Rob, You don't synclock variables, you synclock blocks of code.
Synclock establishes a walled gate around a piece of code and only
allows one thread through the gate at a time.
Are you sure about this?
Rob is correct, IMHO.
Yes the SyncLock itself is around a block of code, however is not its
real intent to protect one or more 'shared' variables?
It's intent is to create a critical section to protect any shared
resource. That may not necessarily be a shared/member variable.
In other words why protect a block of code that does not reference
'shared' variables?
Two threads writing to a file... They may not share a variable, but
they may share access to the file. Its about shared resources.
--
Tom Shelton
MVP [Visual Basic]
Not trying to split anything with anyone :-)
I'm just under the impression that Bob has been led to believe that if he
uses a variable in the parens of the synclock statement, it will lock that
variable, which isn't entirely correct.
I hope he got the meaning of what I was saying :-)
-Rob Teixeira [MVP]
"Jay B. Harlow [MVP - Outlook]" <Ja************@msn.com> wrote in message
news:e2**************@tk2msftngp13.phx.gbl... Rob,
You need to make sure it helps Bob Day!
As I totally agree with what you & Tom are saying, I'm just trying to
ensure you say it in a way that Bob Day understands!
Its is not worth my time to "split hairs" with you!
Jay
On 2004-01-01, Jay B. Harlow [MVP - Outlook] <Ja************@msn.com> wrote: Tom,
You need to make sure it helps Bob Day!
I agree. I hope it does help him. I just don't want Bob to have the
wrong impression as to what a SyncLock is about...
As I totally agree with what you & Tom are saying, I'm just trying to ensure
you say it in a way that Bob Day understands!
Understood.
Its is not worth my time to "split hairs" with you!
I'm not trying to split hairs - it's just that as Rob said, Bob seems to
have a misunderstanding about the intent of SyncLock. I thought Robs,
explanation was right on...
--
Tom Shelton
MVP [Visual Basic] This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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