CS361 Slides - Week 12

Course Information

  • Course Title: CS 361: Computer Systems II

  • Instructor: Prof. Michael S. Kirkpatrick

  • Week: 12, Spring 2024

  • Institution: James Madison University (JMU)

Concept Testing

Thread Output Consistency

  • Code:

    void * child (void *args) {
  int x = 5;
  printf ("%d\n", ++x);
  pthread_exit (NULL);
}

  • Conclusion: Both threads' outputs are the same (each prints 6) because x is a local variable.

Process Structure

  • Process Components:

    • Stack: Memory used for function calls and local variables.

    • Data: Static variables and heap memory.

    • Code: Executable code of the program.

  • Thread Benefits:

    • Modularity

    • Parallel execution

    • Faster/more flexible than processes

    • A necessity in modern computing.

Hardware Considerations

  • Clock Rates:

    • Inquiry about the clock rate on personal computers.

    • Discussion of a hypothetical 52 THz CPU.

Intel Pentium Processors

  • Historical Overview:

    • The Pentium 4 had notable increases in clock rate and power consumption but less performance enhancement.

    • The Prescott version faced thermal issues, leading to the discontinuation of the Pentium 4 line.

    • The Core series adopted a simpler pipeline architecture with lower clock rates but supported multiple processors per chip.

Multithreading Concepts

Types of Threads

  • POSIX Threads

  • Green Threads

  • Fibers

  • Lightweight Processes:

    • Examples include JVM threads, kernel threads, etc.

Forking and Thread Creation

Code Example for Forking

  • Code:

    int main (int argc, char* argv[]) {
  pid_t pid = fork();
  if (pid > 0)
    wait (NULL); /* parent */
  else
    printf ("hello\n"); /* child */
  return 0;
}

  • Basic Operation: This code shows a process creating a child process using fork.

Creating and Managing Threads

  • Thread Creation and Management:

    • Each thread can be created using:

    pthread_create (&thread, NULL, hello, NULL);
pthread_join(thread, NULL);

  • Function to be executed by the thread:

    void * hello (void *args) {
  printf("hello\n");
  pthread_exit (NULL);
}

Comparing Process Creation and Thread Creation

  • Process ID (PID) vs. Thread ID (TID)

    • Differences include resource allocation and management overhead.

  • Thread Function Prototype:

    • All thread entry functions take and return void*.

Activity: Passing Arguments to Threads

Multi-Argument Handling

  1. Same Type: Simple handling in arrays.

  2. Different Types: Use structures to encapsulate multiple types.

  3. Return Structures: Allocated memory structures or pointers.

Example of Argument Passing

  • Addition Function:

    void *add(void * _args) {
  int *args = (int*) _args;
  int x = args[0];
  int y = args[1];
  pthread_exit(x + y);
}

Structs in Thread Arguments

Implementation Example

  • Structure for Passing Data:

    typedef struct name_dob {
  char *name;
  char *dob;
} bio_t;

  • Allocation advice: Always ensure allocated data persists beyond thread lifetime.

Potential Issues in Threads

  • Returning Local Variables: Dangerous to return local stack variables that may go out of scope.

    • Sample Problematic Code:

    void * child (void *args) {
  int x = 5;
  pthread_exit(&x);
}

  • Addressing Shared Variables: Make sure thread interactions on shared resources are well-controlled to avoid data races.

    • Issues arise if threads may concurrently modify shared variables without synchronizations.

Final Activity

  • Reflection on Threads in Assembly Language: Understanding how threading interacts at the assembly level can significantly aid in debugging multi-threaded applications.