threadDeath1.cc File Reference

basic thread functionality More...

#include <pthread.h>
#include <iostream>
#include <cstring>

Include dependency graph for threadDeath1.cc:

Go to the source code of this file.

Macros
#define	CHAR_EXAMPLE
	make this a define to use the char * example More...

Functions
void *	myfunc (void *arg)
	user defined function to call More...
void *	func (void *arg)
	a function that calls the user defined function More...
int	main (int argc, char *argv[])

Detailed Description

basic thread functionality

Purpose:

Example program that creates a thread that uses a function that calls a user defined function. Also demonstrates casing examples for the pthread_join(void **) return type. Often the return type from pthread_join() is confusing so we demonstrate a char* or a string* depending on whether CHAR_EXAMPLE is defined within this file (see below).

The intention here is that we want to demonstrate passing pointers around when creating threads and then accessing those pointers as we go allong.

Definition in file threadDeath1.cc.

Macro Definition Documentation

#define CHAR_EXAMPLE

make this a define to use the char * example

Definition at line 24 of file threadDeath1.cc.

Function Documentation

void* func

(

void *

arg

)

a function that calls the user defined function

See myfunc for more details. This function does, however use pthread_exit() to demonstrate the passing of the return_value pointer back through pthread_join() in main

Definition at line 69 of file threadDeath1.cc.

References myfunc().

Referenced by main().

{
  void *return_value = myfunc(arg);
  pthread_exit(return_value);
}

Here is the call graph for this function:

int main	(	int	argc,
		char *	argv[]
	)

Definition at line 81 of file threadDeath1.cc.

References func(), and myfunc().

{
  //a thread id
  pthread_t tid;

  //return var from a pthread_exit()/pthread_join()
  void **ret;

  //a string to pass to myfunc()
  string arg("string from main");

  //##########################################################
  //##########################################################
  cout << "example 1:" << endl;
  //##########################################################

  //call a function tha calls the function
  pthread_create(&tid, (pthread_attr_t *)NULL, func, (void *)&arg);
  
  //join the thread
  pthread_join(tid, ret);

#ifdef CHAR_EXAMPLE
  //demonstrate a char * example
  char *pc = ((char *)(char *)*ret);
  cout << pc << endl;
  delete pc;
#else
  //demonstrate a string * example
  string *ps = ((string *)(string *)*ret);
  cout << *ps << endl;
  delete (string *)ps;
#endif

  //##########################################################
  //##########################################################
  /* Same type of example as above: this one just calls the function
  directly and uses more direct casting when accesing the return
  value from the function.
  */
  //##########################################################
  cout << "\n" << "example 2:" << endl;
  //##########################################################

  //creat thread 
  pthread_create(&tid, (pthread_attr_t *)NULL, myfunc, (void *)&arg);

  //join thread
  pthread_join(tid, ret);

#ifdef CHAR_EXAMPLE
  //access char through casts
  cout << ((char *)(char *)*ret) << endl;
  delete ((char *)(char *)*ret);
#else
  //access string through casts
  cout << *((string *)(string *)*ret) << endl;
  delete ((string *)(string *)*ret);
#endif

  return 0;
}

Here is the call graph for this function:

void * myfunc

(

void *

arg

)

user defined function to call

Purpose:

A user defined function. This function, for demonstration purposes, dynamically creates a string object that will be returned through a call to pthread_join() later on.

Note

This function SHOULD NOT call pthread_exit() as it is intended, in this case, to return to the wrapper function func(). Calling pthread_exit() from here will terminate the thread and will result in "undefined behavior".

Parameters

arg	is a string object pointer passed in as a void *

Returns

a string object that is dynamically allocated

Returns

some object from the heap

Parameters

some

object

Note

this function assumes that arg is a string pointer passed in from main -for demonstration purposes

 \warning do NOT call pthread_exit from here! This function will

behave the same if it is called directly or not and a returning normally does not affect the return_value parameter of a pthread_join().

Definition at line 28 of file threadDeath1.cc.

Referenced by func(), and main().

{
  //print whatever is in arg as a string 
  cout << *(string *)arg << endl;
  
#ifdef CHAR_EXAMPLE
  //demonstrate a char * return
  char *c = new char[256];
  memset(c, 0, 256);
  strcpy(c,"string from myfunc");
  cout << "myfunc returning:" << c <<endl;

  //pthread_exit((void *)c);

  return( (void *)c);

#else
  //demonstrate a string * return.
  string *s = new string("string from myfunc");
  cout << "myfunc returning:" << *s <<endl;

  /* DO NOT CALL pthread_exit from here */
  //pthread_exit((void *)s); 

  return( (void *)s);
#endif
}