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Why Contexts?

Why Contexts?. Parallel libraries require isolation of messages from one another and from the user that cannot be adequately handled by tags. The following examples are due to Marc Snir. Sub1 and Sub2 are from different libraries Sub1(); Sub2(); Sub1a and Sub1b are from the same library

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Why Contexts?

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  1. Why Contexts? • Parallel libraries require isolation of messages from one another and from the user that cannot be adequately handled by tags. • The following examples are due to Marc Snir. • Sub1 and Sub2 are from different libraries Sub1(); Sub2(); • Sub1a and Sub1b are from the same library Sub1a(); Sub2(); Sub1b();

  2. Process 0 Process 1 Process 2 Recv(any) Send(1) Sub1 Recv(any) Send(0) Recv(1) Send(0) Sub2 Recv(2) Send(1) Send(2) Recv(0) Correct Execution of Library Calls

  3. Recv(1) Send(2) Incorrect Execution of Library Calls Process 0 Process 1 Process 2 Recv(any) Send(1) Sub1 Recv(any) Send(0) Send(0) ? Sub2 Recv(2) Send(1) Recv(0) Program hangs (Recv(1) never satisfied)

  4. Recv(any) Send(1) Sub1a Send(0) Recv(2) Send(0) Send(2) Recv(1) Sub2 Send(1) Recv(0) Recv(any) Sub1b Correct Execution of Library Calls with Pending Communication

  5. Recv(any) Send(1) Sub1a Send(0) Recv(2) Send(0) Send(2) Recv(1) Sub2 Send(1) Recv(0) Recv(any) Sub1b Incorrect Execution of Library Calls with Pending Communication Program Runs—but with wrong data!

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