Hello,
I've 3 small programs. First one writes 4K of data contains 'A's into a
file /tmp/pagetest and then lseek() to the begin of the file.
Second one writes 4K of 'Z' into the same file /tmp/pagetest and
then lseek() to the begin of the file. They both do that in a tight
loop. Now, the third program reads 4K of data from /tmp/pagetest
and exit if the 4K data does not contain all 'A's nor 'Z's. 3 programs
run concurrently on the same machine (3.4). No lock in the code whatsoever,
and all 3 programs use pure write() and read(). I thought the third
program would exit pretty quickly since the data in the file may contain
mixed of 'A's and 'Z's, but it has been running for hours and nothing
happened. Could someone kindly explain this? I was told that this is
because the pagesize is 4096 in the kernel, so that read()/write() 4K of
data will not get context switched until the call is compeleted.
Is that right?
I can attach the code if it's necessary.
Thanks
FengYue
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