Image Threads Investigation Report

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TurboIMAGE thread-aware and thread-safe investigation report

by Tien-You Chen

1. Introduction *

1.1 Background *

1.2 Requests *

1.3 Acknowledgements *

2. Problem statement *

2.1 Thread safe *

2.1.1 Runtime control blocks

2.1.2 Global variables

2.1.3 Open files

2.2 Forked processes *

2.2.1 Runtime control blocks

2.2.2 Global variables

2.2.3 Open files

2.3 Passing "base ID" between processes *

3. Options *

3.1 Runtime control blocks *

3.1.1 Copy DBU and DBUX

3.1.2 Share DBU and DBUX

3.2 Global variables *

3.3 Open files *

4. Feedback *

5. Recommendation and estimation *

6. Issues *

Introduction

1.1 Background

In order to respond to users’ requests quickly, this year, 2001, Interex and CSY have teamed

up and taken a different approach to handling the System Improvement Ballot (SIB). First,

each Special Interest Group (SIG) proposed a list of enhancements, less than 10 items, to a

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Summary of content (9 pages)

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Image Threads Investigation Report Page 1 of 9 Jazz home > Papers & Training IMAGE threads investigation report » Return to original page TurboIMAGE thread-aware and thread-safe investigation report by Tien-You Chen 1. Introduction * 1.1 Background * 1.2 Requests * 1.3 Acknowledgements * 2. Problem statement * 2.1 Thread safe * 2.1.1 Runtime control blocks * 2.1.2 Global variables * 2.1.3 Open files * 2.2 Forked processes * 2.2.1 Runtime control blocks * 2.2.2 Global variables * 2.2.3 Open files * 2.
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Image Threads Investigation Report Page 2 of 9 specially formed committee. Second, the committee went through the lists from all the SIGs and picked 20 to 30 enhancements and created a final ballot. After all the users of HP e3000 community have voted, CSY will quickly review the result and choose several items from the top ten and then begin working. The item, which got the most votes, was "make TurboIMAGE thread aware and thread safe". 1.
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Image Threads Investigation Report Page 3 of 9 2.1.1 Runtime control blocks For every DBOPEN user’s program called, a runtime control block named DBU will be created. A DBU contains the information specific to this DBOPEN.
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Image Threads Investigation Report Page 4 of 9 are a few global variables exist, since they have to last and keep the value from one intrinsic call to another intrinsic call. Those variables are created by TurboIMAGE and allocated in the DP area in the SR5 virtual space.
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Image Threads Investigation Report Page 5 of 9 can not be within a transaction while forking, either a dynamic transaction or a user logging transaction. The forking process can not own any locks, no matter if it is a database lock, a data set lock or a predicate lock. And, of course, the forking process can not be in a TurboIMAGE intrinsic at the time of forking.
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Image Threads Investigation Report Page 6 of 9 categories: runtime control blocks, global variables and open files. 3.1 Runtime control blocks There are two ways to handle the runtime control blocks: copy and share. 3.1.1 Copy DBU and DBUX When a process, which already has an open TurboIMAGE database, forks, one way to handle the DBU and DBUX runtime control block is to copy. Copy all the DBUs and the DBUX, which the parent process owned, to the SR5 virtual space of the forked process.
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Image Threads Investigation Report Page 7 of 9 procedure, the performance of the forking will be bad if we choose to copy the DBU(s). ¡ Threads share the same SR5 virtual space. So, if the initial thread opens many databases and then creates many threads, then there may be a space problem if we copy DBU(s) for every thread. ¡ One general concept for thread and forked processes is that they inherit (share) the resource of the parent process.
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Image Threads Investigation Report Page 8 of 9 certain level in order to accommodate the multiple copies of the log record, trailer area …etc. ¡ For every DBOPEN, one "accessor entry" and one DBU will be created. The address of the DBU will be stored in "accessor entry" and the user count will be increased. These three are tightly coupled to each other.
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Image Threads Investigation Report Page 9 of 9 responsibility to keep track of current record pointers if more than one thread would access the same data set in the same database. Many design suggestions such as adding new intrinsics for thread operation to use; implementing "internal MR" to prevent potential deadlock between two PINs (but in the same "thread family"); creating "light-weight" DBU, which contains only things need to be separated etc. are also mentioned in their feedback. 5.