Context Switching Question

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Hi, I'm creating a small C#program that communicates through the serial port.
I have a separate thread that continuously takes in data from an external
device in a while loop. The problem is that when I try and run another
program, open a menu, or anything, I miss getting bytes. If I set the threads
priority to above normal it works fine, but the rest of the program slows
down dramatically. Is there any command or way to ensure that a block of code
will execute together and not get context switched out in the middle? If
there is, then my problem is solved. I can send a command to the external
device saying I'm ready for the next byte, and be assured that I'll get it if
I can execute those commands together in a block. Any advice would be
appreciated. Thanks.
 
JRB,

How are you reading the bytes from the serial port to begin with? To be
honest, I doubt that context switching is the issue here, but rather, how
you access the bytes, and other operations that you might be performing.
 
Hi, here is the part in my code that is relevant. Might be some syntax errors
as I didn't copy and paste it, buy you'll get the idea. This is basically
what is running in the thread that gets started and stopped from a button on
my GUI.

byte[] b = null;
byte firstByte = 0;
byte secondByte = 0;
int nBytes = 0;

while(true)
{
Port.Send("A"); //Something to start transaction with device.

nBytes = 0;

//Read from port until actually recieve something.
do
{
nBytes = Port.Recv(out b); //Port.Recv returns how many bytes recieved.
} while(nBytes == 0);

firstByte = b[0];

nBytes = 0;

//Wait to recieve seond byte.
do
{
nBytes = Port.Recv(out b);
} while(nBytes == 0);

secondByte = b[0];

//I do this 8 times to get 8 bytes that the device sends successively.
//The device waits for 100 milliseconds after each time it sends a byte
in order
//to make sure that I'm in the do-while loop.
//Then when the user clicks stop, runningThread gets set to stop.

if(runningThread == false)
break;

}

Like I said, if I just let the program run without trying to open up any
other programs, or do anything, it works fine. But when I start doing other
things, one of the bytes gets missed. So for the 8th byte, the program and
the device are locked. My program is waiting to recieve a byte in the last
do-while loop, and the device has looped back and is waiting for the "A" to
be sent to start another cycle. If there was a way to lock 2 statements
together so there can't be a switch in between them then I can send a start
character before each do-while statement to the device to say "I'm ready for
another byte". Then I can drop into the do-while loop and wait for it. If I
can't be assured that both statements will execute one after another with no
switching, there is a possibility that there could be a context switch after
I send the statement to say I'm ready for a byte, then my program will miss a
byte again and be locked waiting for a byte, while the device is locked
waiting for the next "I'm ready" statement. Any thoughts would be
appreciated. Thanks.

Nicholas Paldino said:
JRB,

How are you reading the bytes from the serial port to begin with? To be
honest, I doubt that context switching is the issue here, but rather, how
you access the bytes, and other operations that you might be performing.


--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

JRB said:
Hi, I'm creating a small C#program that communicates through the serial
port.
I have a separate thread that continuously takes in data from an external
device in a while loop. The problem is that when I try and run another
program, open a menu, or anything, I miss getting bytes. If I set the
threads
priority to above normal it works fine, but the rest of the program slows
down dramatically. Is there any command or way to ensure that a block of
code
will execute together and not get context switched out in the middle? If
there is, then my problem is solved. I can send a command to the external
device saying I'm ready for the next byte, and be assured that I'll get it
if
I can execute those commands together in a block. Any advice would be
appreciated. Thanks.
Click to expand...
Click to expand...
 
Hi JRB:

I dont know what the Port class is, but looking at the code I'd guess
it possible for it to return all 8 bytes on the first call to Recv,
but the code assumes it will only return 1.

--
Scott
http://www.OdeToCode.com/blogs/scott/

Hi, here is the part in my code that is relevant. Might be some syntax errors
as I didn't copy and paste it, buy you'll get the idea. This is basically
what is running in the thread that gets started and stopped from a button on
my GUI.

byte[] b = null;
byte firstByte = 0;
byte secondByte = 0;
int nBytes = 0;

while(true)
{
Port.Send("A"); //Something to start transaction with device.

nBytes = 0;

//Read from port until actually recieve something.
do
{
nBytes = Port.Recv(out b); //Port.Recv returns how many bytes recieved.
} while(nBytes == 0);

firstByte = b[0];

nBytes = 0;

//Wait to recieve seond byte.
do
{
nBytes = Port.Recv(out b);
} while(nBytes == 0);

secondByte = b[0];

//I do this 8 times to get 8 bytes that the device sends successively.
//The device waits for 100 milliseconds after each time it sends a byte
in order
//to make sure that I'm in the do-while loop.
//Then when the user clicks stop, runningThread gets set to stop.

if(runningThread == false)
break;

}

Like I said, if I just let the program run without trying to open up any
other programs, or do anything, it works fine. But when I start doing other
things, one of the bytes gets missed. So for the 8th byte, the program and
the device are locked. My program is waiting to recieve a byte in the last
do-while loop, and the device has looped back and is waiting for the "A" to
be sent to start another cycle. If there was a way to lock 2 statements
together so there can't be a switch in between them then I can send a start
character before each do-while statement to the device to say "I'm ready for
another byte". Then I can drop into the do-while loop and wait for it. If I
can't be assured that both statements will execute one after another with no
switching, there is a possibility that there could be a context switch after
I send the statement to say I'm ready for a byte, then my program will miss a
byte again and be locked waiting for a byte, while the device is locked
waiting for the next "I'm ready" statement. Any thoughts would be
appreciated. Thanks.

Nicholas Paldino said:
JRB,

How are you reading the bytes from the serial port to begin with? To be
honest, I doubt that context switching is the issue here, but rather, how
you access the bytes, and other operations that you might be performing.


--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

JRB said:
Hi, I'm creating a small C#program that communicates through the serial
port.
I have a separate thread that continuously takes in data from an external
device in a while loop. The problem is that when I try and run another
program, open a menu, or anything, I miss getting bytes. If I set the
threads
priority to above normal it works fine, but the rest of the program slows
down dramatically. Is there any command or way to ensure that a block of
code
will execute together and not get context switched out in the middle? If
there is, then my problem is solved. I can send a command to the external
device saying I'm ready for the next byte, and be assured that I'll get it
if
I can execute those commands together in a block. Any advice would be
appreciated. Thanks.
Click to expand...
Click to expand...
Click to expand...
 
Hi, I'm not sure what you mean by port class. I'm reading in from a standard
serial port. RS-232. I haven't tried reading in all 8 bytes. I wasn't sure
how big the Rx buffer is, so thought it would be safer to read in one by one.
How many bytes will Rx hold before overflow? Thanks.

JRB

Scott Allen said:
Hi JRB:

I dont know what the Port class is, but looking at the code I'd guess
it possible for it to return all 8 bytes on the first call to Recv,
but the code assumes it will only return 1.

--
Scott
http://www.OdeToCode.com/blogs/scott/

Hi, here is the part in my code that is relevant. Might be some syntax errors
as I didn't copy and paste it, buy you'll get the idea. This is basically
what is running in the thread that gets started and stopped from a button on
my GUI.

byte[] b = null;
byte firstByte = 0;
byte secondByte = 0;
int nBytes = 0;

while(true)
{
Port.Send("A"); //Something to start transaction with device.

nBytes = 0;

//Read from port until actually recieve something.
do
{
nBytes = Port.Recv(out b); //Port.Recv returns how many bytes recieved.
} while(nBytes == 0);

firstByte = b[0];

nBytes = 0;

//Wait to recieve seond byte.
do
{
nBytes = Port.Recv(out b);
} while(nBytes == 0);

secondByte = b[0];

//I do this 8 times to get 8 bytes that the device sends successively.
//The device waits for 100 milliseconds after each time it sends a byte
in order
//to make sure that I'm in the do-while loop.
//Then when the user clicks stop, runningThread gets set to stop.

if(runningThread == false)
break;

}

Like I said, if I just let the program run without trying to open up any
other programs, or do anything, it works fine. But when I start doing other
things, one of the bytes gets missed. So for the 8th byte, the program and
the device are locked. My program is waiting to recieve a byte in the last
do-while loop, and the device has looped back and is waiting for the "A" to
be sent to start another cycle. If there was a way to lock 2 statements
together so there can't be a switch in between them then I can send a start
character before each do-while statement to the device to say "I'm ready for
another byte". Then I can drop into the do-while loop and wait for it. If I
can't be assured that both statements will execute one after another with no
switching, there is a possibility that there could be a context switch after
I send the statement to say I'm ready for a byte, then my program will miss a
byte again and be locked waiting for a byte, while the device is locked
waiting for the next "I'm ready" statement. Any thoughts would be
appreciated. Thanks.

Nicholas Paldino said:
JRB,

How are you reading the bytes from the serial port to begin with? To be
honest, I doubt that context switching is the issue here, but rather, how
you access the bytes, and other operations that you might be performing.


--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Hi, I'm creating a small C#program that communicates through the serial
port.
I have a separate thread that continuously takes in data from an external
device in a while loop. The problem is that when I try and run another
program, open a menu, or anything, I miss getting bytes. If I set the
threads
priority to above normal it works fine, but the rest of the program slows
down dramatically. Is there any command or way to ensure that a block of
code
will execute together and not get context switched out in the middle? If
there is, then my problem is solved. I can send a command to the external
device saying I'm ready for the next byte, and be assured that I'll get it
if
I can execute those commands together in a block. Any advice would be
appreciated. Thanks.
Click to expand...
Click to expand...
Click to expand...
 
Hi JRB:

I'm talking about this line of code:

nBytes = Port.Recv(out b);

The comment next to the line of code says "Port.Recv returns how many
bytes recieved.", but that return value (nBytes) is never checked. I'd
bet money you occasionaly get back more than a single byte.

--
Scott
http://www.OdeToCode.com/blogs/scott/

Hi, I'm not sure what you mean by port class. I'm reading in from a standard
serial port. RS-232. I haven't tried reading in all 8 bytes. I wasn't sure
how big the Rx buffer is, so thought it would be safer to read in one by one.
How many bytes will Rx hold before overflow? Thanks.

JRB

Scott Allen said:
Hi JRB:

I dont know what the Port class is, but looking at the code I'd guess
it possible for it to return all 8 bytes on the first call to Recv,
but the code assumes it will only return 1.

--
Scott
http://www.OdeToCode.com/blogs/scott/

Hi, here is the part in my code that is relevant. Might be some syntax errors
as I didn't copy and paste it, buy you'll get the idea. This is basically
what is running in the thread that gets started and stopped from a button on
my GUI.

byte[] b = null;
byte firstByte = 0;
byte secondByte = 0;
int nBytes = 0;

while(true)
{
Port.Send("A"); //Something to start transaction with device.

nBytes = 0;

//Read from port until actually recieve something.
do
{
nBytes = Port.Recv(out b); //Port.Recv returns how many bytes recieved.
} while(nBytes == 0);

firstByte = b[0];

nBytes = 0;

//Wait to recieve seond byte.
do
{
nBytes = Port.Recv(out b);
} while(nBytes == 0);

secondByte = b[0];

//I do this 8 times to get 8 bytes that the device sends successively.
//The device waits for 100 milliseconds after each time it sends a byte
in order
//to make sure that I'm in the do-while loop.
//Then when the user clicks stop, runningThread gets set to stop.

if(runningThread == false)
break;

}

Like I said, if I just let the program run without trying to open up any
other programs, or do anything, it works fine. But when I start doing other
things, one of the bytes gets missed. So for the 8th byte, the program and
the device are locked. My program is waiting to recieve a byte in the last
do-while loop, and the device has looped back and is waiting for the "A" to
be sent to start another cycle. If there was a way to lock 2 statements
together so there can't be a switch in between them then I can send a start
character before each do-while statement to the device to say "I'm ready for
another byte". Then I can drop into the do-while loop and wait for it. If I
can't be assured that both statements will execute one after another with no
switching, there is a possibility that there could be a context switch after
I send the statement to say I'm ready for a byte, then my program will miss a
byte again and be locked waiting for a byte, while the device is locked
waiting for the next "I'm ready" statement. Any thoughts would be
appreciated. Thanks.

:

JRB,

How are you reading the bytes from the serial port to begin with? To be
honest, I doubt that context switching is the issue here, but rather, how
you access the bytes, and other operations that you might be performing.


--
- Nicholas Paldino [.NET/C# MVP]
- (e-mail address removed)

Hi, I'm creating a small C#program that communicates through the serial
port.
I have a separate thread that continuously takes in data from an external
device in a while loop. The problem is that when I try and run another
program, open a menu, or anything, I miss getting bytes. If I set the
threads
priority to above normal it works fine, but the rest of the program slows
down dramatically. Is there any command or way to ensure that a block of
code
will execute together and not get context switched out in the middle? If
there is, then my problem is solved. I can send a command to the external
device saying I'm ready for the next byte, and be assured that I'll get it
if
I can execute those commands together in a block. Any advice would be
appreciated. Thanks.
Click to expand...
Click to expand...
Click to expand...
 
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