Petri net
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The document describes a Petri net model with two processes, A and B, that access two files, F1 and F2. The model contains places representing the states of each process starting, accessing the first file, and accessing both files. It also contains transitions representing each process taking the first file, taking the second file, and finishing. The files are represented by tokens in places F1 and F2, and initially the processes are represented as started by tokens in their starting places. The model demonstrates how the processes accessing the files in different orders can result in a deadlock situation.
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Petri net
- 1. Petri Net
- 2. The next Petri net model contains two processes A and B accessing the files F1 and F2. For both processes there are places representing the following states: - the process has been started . - the process uses the first file (F1 for the process A, F2 for B) . - the process uses both files .
- 3. For both processes there are transitions representing the following actions: - the process takes the first file (F1 for the process A, F2 for B), - the process takes the second file (F2 for the process A, F1 for B), - the process finishes.
- 4. The files are modeled by tokens in places F1 and F2 respectively. The tokens in places "process starts" represent the fact, that the processes have been started. At the beginning there are two enabled transitions (both processes may start). The second step decides whether there will be a deadlock or not. If both processes take one file, no process can continue. If the process which took the first file takes also the second one, everything is OK. The next example shows the solution to this deadlock problem.
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