Databases
StackOverflow2013
Postsdbo
POExplanation for behaviour of code
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POExplanation for behaviour of code
    primarykey
    data
    text
    <p>I was following the multithreading tutorial from <a href="https://computing.llnl.gov/tutorials/pthreads" rel="nofollow">https://computing.llnl.gov/tutorials/pthreads</a> and experimenting with some of the code provided.</p> <p>I used this source file <a href="https://computing.llnl.gov/tutorials/pthreads/samples/hello.c" rel="nofollow">https://computing.llnl.gov/tutorials/pthreads/samples/hello.c</a> then added this to the main function:</p> <pre><code> void * v; v = (void *)t; </code></pre> <p>and replaced this line:</p> <pre><code>rc = pthread_create(threads+t, NULL, PrintHello, (void*)t); </code></pre> <p>by this:</p> <pre><code>rc = pthread_create(threads+t, NULL, PrintHello, v) </code></pre> <p>Arguably(I know it's not a good argument :) ), the output should have remained unchanged.. but this is the new output:</p> <pre><code>In main: creating thread 0 In main: creating thread 1 Hello World! It's me, thread #140734232544832! In main: creating thread 2 In main: creating thread 3 Hello World! It's me, thread #140734232544832! In main: creating thread 4 Hello World! It's me, thread #140734232544832! Hello World! It's me, thread #140734232544832! Hello World! It's me, thread #140734232544832! </code></pre> <p>Thread # is garbage! </p> <p>Can someone explain to me what's going on here? Why is the output changed?</p> <p>Is it because t was being passed by value and casted while being passed to PrintHello while now, after the change I am attempting to pass pointer and while the address of that pointer is passed properly - that address does not contain the value t contains since that was local to main?</p> <p>Can someone please confirm/ reject and fix my theory?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USuser657862
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POExplanation for behaviour of code
      1. This table or related slice is empty.
      1. VTDownMod
    1. COyou need to show us where you added `void* v` and the follwing line in the main
      singulars
      1. POExplanation for behaviour of code
      1. USpippin1289
    2. COah, of course. v gets the value of t. which right after `long t`, `t` has an undefined value. put it inside the for loop instead.
      singulars
      1. POExplanation for behaviour of code
      1. USpippin1289
    3. COThanks pippin1289. I had completely ignored the most common suspicion and was wondering instead if this was due to casting at the time of calling the function - which of course was an invalid suspicion. After moving the v = (void *)t into the loop it works the way I expected it to :)
      singulars
      1. POExplanation for behaviour of code
      1. USuser657862
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload