Non-Reentrant VI executing in different Process Stacks
I am creating a DLL which can be called by several different processes on a machine at the same time. If I have a non-reentrant VI in the API, do the same restrictions apply between processes as if they were in the same process? For example, if I call "Get Shorty.vi" which is a non-reentrant VI from 2 places in the same process, at the same time, the first call will start executing, and the second call will wait till the first call is done. When called from 2 different process stacks, there is supposed to be total seperation of memory windows, so logic tells me that this restriction would not apply if that same VI were called from 2 different processes.
The catch is that the VI Library installed by the run-time engine is used by both processes as well. Would this, in effect, cause the same behavior between 2 calls to the same VI both in process and out?
Thanks for any help you can provide. This is not a easy to describe concept, so feel free to ask for clarification if needed.
CyberTazer
Software Systems Engineer
I understand that the memory spaces are supposed to be completly seperate. The question is that if 2 processes call the same function in the same dll at the same time... will one process have to wait on the other process to finish before being allowed to execute? My feeling on this is no, it would not have to wait, but I am hoping that someone out there has a more difinitive answer.
There is no shared memory mechanisms set up in this vi.. ie for persistant data between execution processes. I am not even sure if this is possible with LV dll's, but I thought I would throw that in there since I know it is possible in general.
Thanks again for your help guys... keep em comming. Hopefully this will help clear up other peoples perceptions on how dll execution is handled in LV if we can nail this down a bit more.
CyberTazer
Software Systems Engineer
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Hi,
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This is preventing other threads from entering this synchronized block until it has completed, but it looks to me like the same thread entering this method again with another request is allowed to go through, because the thread already has the lock on this email address object.
This is causing data to be saved twice because in the short time between when I check if a record already exists in the database and when a new one has been saved another request sneeks in and also saves a record.
How can I prevent the same thread from entering this block again with another request until processing has finished for this email?
I suspect it has something to do with non-reentrant locking, but I don't understand a word of what I've read about it so far.
Thanks in advance,
EvertI don't know if this is the problem with your
program, but what you describe is possible: in Java
(differing from POSIX threads) a thread can access a
single lock (a synchronized method) more than once.
It's called reentrant locking.I assume that in practice this can really just happen if I have a method that calls itself. In my case with a web application, I assume the thread would complete one request completely before starting with the next http request. Other threads might interject, but the same thread should finish one request before starting the next.
I've done what BinaryDigit suggested and synchronized on email.intern() instead of just on email, and it looks like that did the trick. After 6 years of Java programming, I've forgotten that two strings are not necessarily == when they are equal. It's time for me to grab my beginner Java books again! -
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This query takes 5 seconds to execute on Development environment to get 200 records but the same query takes around 50 seconds to execute on Alpha environment and to retrieve same number of records.
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CPU used by this session 1741
CPU used when call started 1741
Cached Commit SCN referenced 15634
DB time 1752
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Number of read IOs issued 173
SQL*Net roundtrips to/from client 14
buffer is not pinned count 90474
buffer is pinned count 264554
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bytes sent via SQL*Net to client 28859
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calls to kcmgcs 13
cell physical IO interconnect bytes 165330944
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commit txn count during cleanout 5273
consistent gets 202533
consistent gets - examination 101456
consistent gets direct 19686
consistent gets from cache 182847
consistent gets from cache (fastpath) 81013
enqueue releases 3
enqueue requests 3
execute count 6
file io wait time 1582
immediate (CR) block cleanout applications 5273
index fetch by key 36608
index scans kdiixs1 36582
no buffer to keep pinned count 8
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non-idle wait count 42
non-idle wait time 2
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parse count (hard) 1
parse count (total) 6
parse time cpu 1
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physical read IO requests 181
physical read bytes 163299328
physical read total IO requests 181
physical read total bytes 163299328
physical read total multi block requests 162
physical reads 19934
physical reads direct 19934
physical reads direct temporary tablespace 248
physical write IO requests 8
physical write bytes 2031616
physical write total IO requests 8
physical write total bytes 2031616
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physical writes direct 248
physical writes direct temporary tablespace 248
physical writes non checkpoint 248
recursive calls 31
recursive cpu usage 1
rows fetched via callback 23018
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session logical reads 202533
session uga memory max 65488
sorts (memory) 3
sorts (rows) 19516
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table fetch by rowid 140921
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table scan rows gotten 2012896
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table scans (long tables) 2
user I/O wait time 2
user calls 16
workarea executions - onepass 4
workarea executions - optimal 7
workarea memory allocated 17
------------------------------------------------------ For Alpha ------------------------------------------------------------------
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Commit SCN cached 1
DB time 6999
Effective IO time 4262103
Number of read IOs issued 2155
OS All other sleep time 10397
OS Chars read and written 340383180
OS Involuntary context switches 18766
OS Other system trap CPU time 27
OS Output blocks 12445
OS Process stack size 24576
OS System call CPU time 223
OS System calls 20542
OS User level CPU time 5526
OS User lock wait sleep time 86045
OS Voluntary context switches 15739
OS Wait-cpu (latency) time 273
SQL*Net roundtrips to/from client 14
buffer is not pinned count 2111
buffer is pinned count 334
bytes received via SQL*Net from client 4486
bytes sent via SQL*Net to client 28989
calls to get snapshot scn: kcmgss 510
calls to kcmgas 4
calls to kcmgcs 119
cell physical IO interconnect bytes 340041728
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cleanouts only - consistent read gets 1
cluster key scan block gets 179
cluster key scans 168
commit txn count during cleanout 1
consistent gets 41298
consistent gets - examination 722
consistent gets direct 30509
consistent gets from cache 10789
consistent gets from cache (fastpath) 9038
cursor authentications 2
db block gets 7
db block gets from cache 7
dirty buffers inspected 1
enqueue releases 58
enqueue requests 58
execute count 510
file io wait time 6841235
free buffer inspected 8772
free buffer requested 8499
hot buffers moved to head of LRU 27
immediate (CR) block cleanout applications 1
index fast full scans (full) 1
index fetch by key 196
index scans kdiixs1 331
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parse count (total) 44
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physical reads cache 8498
physical reads cache prefetch 7467
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physical write IO requests 126
physical write bytes 10764288
physical write total IO requests 126
physical write total bytes 10764288
physical writes 1314
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physical writes direct temporary tablespace 1314
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prefetched blocks aged out before use 183
recursive calls 1329
recursive cpu usage 76
rows fetched via callback 7
session cursor cache count 8
session cursor cache hits 491
session logical reads 41305
session pga memory max 851968
session uga memory -660696
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shared hash latch upgrades - no wait 14
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sorts (rows) 21371
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table fetch by rowid 613
table scan blocks gotten 30859
table scan rows gotten 3738599
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table scans (long tables) 8
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workarea executions - optimal 113
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