December 2, 2008 06:20pm pst

1. Infinity08 578,921
2. sunnycoder 226,870
3. evilrix 176,915
4. jkr 159,159
5. ozo 115,519
6. Kdo 90,690
7. jaime_oliv... 58,140
8. itsmeandn... 55,011
9. josgood 45,657
10. fridom 40,492
11. LordOfPo... 17,652
12. Mysidia 15,348
13. Gurudenis 14,530
14. JohnGaby 14,500
15. duncan_roe 12,950
16. FentonEng 12,200
17. sweetfa2 11,500
18. peetm 11,260
19. ravenpl 9,890
20. Anthony... 9,692
21. trinitrotolu... 8,530
22. hielo 7,700
23. DanRollins 7,240
24. ikework 7,100
25. cup 6,640

1. Infinity08 1,111,780
2. sunnycoder 1,013,413
3. Kdo 817,188
4. jkr 769,921
5. ozo 457,827
6. grg99 297,356
7. PaulCasw... 296,971
8. jaime_oliv... 213,812
9. evilrix 206,780
10. itsmeandn... 183,477
11. brettmjohn... 182,528
12. fridom 171,096
13. ankuratvb 157,866
14. imladris 141,517
15. cwwkie 129,383
16. Axter 98,363
17. akshayxx 96,671
18. josgood 79,717
19. AlexViroc... 70,328
20. gj62 70,227
21. rbr 69,997
22. ssnkumar 61,996
23. rajeev_d... 60,229
24. efn 57,946
25. alexo 56,489

04.30.2008 at 06:02PM PDT, ID: 23367376

	[x] Attachment Details

[x]

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9.0

Synchronization question

Asked by CyrexCore2k in C Programming Language, C++ Programming Language

I've been trying to figure out when and where a context switch can occur. I thought I understood it but a program I wrote seems to be proving me wrong.

Here's the setup. I've declared a global unsigned int val and in my main method I give it the value 2097152. I also created a global volatile char called hold which I've set to false in the main method. I then create 10 threads and have them run the following function:

void * thread_work(void * parameters)
{
while(hold) {}
val = val / 2;
return NULL;
}

As soon as all the threads are created main will set hold to some value that evaluates to false. (I did this because I didn't want any threads executing while I'm still creating the others.)

Here's my question, why am I consistently getting the result 2048? Shouldn't I be getting random power of 2 values between that and 1048576? I thought the code might execute something like this:

thread1 moves memory value into register
thread1 divides value (lets say it's the first one so 1048576)
*context switch*
thread2 moves memory value into register (still 2097152)
thread2 divides value (lets say it's the first one so 1048576)
thread2 moves register value back into memory
*context switch*
thread1 moves register value back into memory

Which would make the result 4096 at least... so why isn't this happening? What am I misunderstanding here?Start Free Trial

Keywords: Synchronization question

	Title
1	volatile??
2	Volatile optimizations
3	Volatile
4	volatile variable
5	what is volatile in java . how it is used
6	Question with regard to Volatile type s…

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20081112-EE-VQP-44 / EE_QW_EXPERT_20070906

Synchronization question

Asked by CyrexCore2k in C Programming Language, C++ Programming Language

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