=Paper=
{{Paper
|id=None
|storemode=property
|title=PNTM Integration of Petri Nets and Transactional Memory
|pdfUrl=https://ceur-ws.org/Vol-723/paper15.pdf
|volume=Vol-723
|dblpUrl=https://dblp.org/rec/conf/apn/WuZWD11
}}
==PNTM Integration of Petri Nets and Transactional Memory==
https://ceur-ws.org/Vol-723/paper15.pdf
PNTM – Integration of Petri Nets and
Transactional Memory
Weiyi Wu, Yao Zhang, Shengyuan Wang, and Yuan Dong
Department of Computer Science and Technology , Tsinghua University, Beijing,
100084, China
w1w2y3@gmail.com wwssyy@tsinghua.edu.cn
PNTM demonstrates a new concurrent programming model, providing explicit
concurrency among cooperative transactions with correctness. It integrates a
special Petri net and transactional memory, and improves the performance of
transactions by decreasing the rate of conflicts. The GUI part of PNTM
environment is based on PNK [1], the compiler is a modified GJC [2], and the
runtime is based on DSTM2 [3].
Editor The IDE provides a simple GUI with a code editor and a net editor.
The editor for Petri net system is modified from PNK. All elements can have
extra fields and be edited visually. The extra fields such as resources in places
and code in transitions all correspond special variables and functions in the
code, as in Table 1.
Table 1. Extra fields in Petri nets’ elements and corresponding elements in code
code in transition petrinet function name
resource in place resource variable
inscription in arc resource variable
Virtual Machine The code editor can compile code along with Petri nets.
Before compilation, the Petri nets are interpreted to internal representation for
static check. In order to guarantee correctness at the level of Petri nets, the
Petri net must meet constraints below:
1. All resources must have different names.
2. One resource should appear at no more than one place at any time.
3. The input arcs to one transition should have no common resource.
4. The output arcs from one transition should have no common resource. Be-
sides, the resources in output arcs must be the subset of resources in input
arcs.
After checking the correctness at the level of Petri nets, the editor will append
a piece of code for building Petri Net simulator at runtime. Hence the simulator
is created and initialized at runtime. The runtime provide 5 APIs as below:
W. Wu, Y. Zhang, S. Wang, Y. Dong: Petri Nets and Transactional Memory 197
1. AddTransition(transition, code) adds transition.
2. AddPlace(place, resource) adds place.
3. AddArc(source, target, inscription) adds arc.
4. Start() starts simulation.
5. Join() terminates simulation.
The runtime is a Petri nets VM using DSTM2. The first 3 API can build
up a simulator of a Petri net and the last 2 API control the simulator. The
simulator allocate a DSTM2 Thread for every transition in the net. The Threads
are all waiting for notification. Only notified Thread can consume resources,
call function and produce new resources. A global lock is used to protect all
resources in order to make manipulation on resources atomic and prevent dead-
lock. Some optimizations accelerate the check-and-consume process. Hence the
overhead is relatively low. When the transition consumes resources and is ready
to fire, corresponding petrinet function is called using reflection. If all global
variables protected by STM successfully commit, the transition will produce new
resources. Otherwise the transition will revert all state and return consumed
resources.
Compilation At the early stage of compilation, the compiler will recognize
and mark new keyword petrinet, resource, global. The global variables
need to transform to instances of pre-defined interfaces in order to meet
requirement of DSTM2’s APIs. For example, equivalent code to transformed
“global int a;” is shown in Table 2. AInt refers to “Atomic Integer”.
Table 2. Equivalent code to transformed code
original code equivalent code pre-defined interface
@atomic interface AInt {
int getValue ();
AInt a = void setValue (int value);
global int a;
factory_AInt.create(); }
Factory factory_AInt =
Thread.makeFactory(AInt.class);
After AST is built, the compiler will check the semantic correctness. The
functions with petrinet modifier and Petri nets themselves should meet con-
straints below:
1. petrinet function must have function body.
2. petrinet function should have no parameter.
3. Only resource, global and local variables can be used in a petrinet func-
tion.
4. Only petrinet function can be called in transition.
5. Resources in incoming arcs of a transition must be a superset of all resource
variable used in corresponding petrinet function.
198 PNSE’11 – Petri Nets and Software Engineering
In addition, all references of global variables and all left-values consisted
of global variables must be transformed to proper getter and setter in order
to meet requirement of DSTM2’s API. Equivalent code to getter and setter is
shown in Table 3.
Table 3. Equivalent code to getter and setter
transform type original code equivalent code
initializer global int a = 0; ...;a.setValue(0);
reference x = a + 1; x = a.getValue() + 1;
left-value a = x + 1; a.setValue(x + 1);
self-operation a++; a.setValue(a.getValue() + 1);
The rest of compilation is the same with GJC.
Future Work We are making efforts to some basic performance evaluation.
References
1. INA:Integrated Net Analyzer, at http://www.informatik.hu-
berlin.de/lehrstuehle/automaten/ina.
2. GJC available at : http://www.sun.com/software/communitysource/j2se
3. Maurice Herlihy, Victor Luchangco, Mark Moir, A Flexible Framework for Imple-
menting Software Transactional Memory, In Preceedings of OOPSLA’06, Pages 253-
262, 2006.