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322
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1 OS
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2 ==
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272
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3
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322
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4 Design
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5 ------
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273
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6
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7 Processes / threads
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8 ~~~~~~~~~~~~~~~~~~~
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272
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9
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10 Processes are completely seperated and fully pre-emptive.
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11 This means a process can be unscheduled at any moment.
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12
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13 Threads are co-operative. This means they yield control
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14 voluntary. This means that mutexes and locks are not required.
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15 This is done with the built-in language feature called tasks.
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16
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17 If some heavy duty task must be performed, either way spawn
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18 a new process, or yield frequently from this hard labour.
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19
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273
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20 tasks
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21 ~~~~~
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272
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22
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273
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23 Consider the following:
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24
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25 .. code::
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272
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26
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273
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27 function int insanemath(int a)
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272
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28 {
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273
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29 while (a > 0)
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30 {
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31 a = a -1;
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32 resume agent1;
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33 }
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34 return a - 1;
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272
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35 }
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36
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273
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37 task agent1()
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38 {
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39 start agent2;
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40 }
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272
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41
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273
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42 task agent2()
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43 {
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44 insanemath(55);
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45 insanemath(44);
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46 }
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272
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47
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273
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48 task main()
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49 {
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50 start agent1;
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51 join agent1;
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52 }
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53
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272
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54
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55 Say to tasks are running in concurrent / parallel.
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56
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57
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58
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59 Stack layout for tasks.
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60 ||
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61 ||
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62 \/
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63 +---------+
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64 | return address
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65 | locals
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66 |
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67 +------
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68 | return address
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69 | locals
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70 |
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71 +---
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72
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73 Assembly code for the functions above:
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74
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273
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75 .. code::
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76
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77 .code
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78 insanemath:
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79 L1:
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80 load r0, sp - 4
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81 cmp r0, 0
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82 jl L2
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83 dec r0
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84 store r0, sp - 4
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85 jmp L1
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86 L2:
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87 ret
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272
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88
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273
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89 agent1:
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90 hlt?
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272
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91
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273
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92 agent2:
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93 hlt?
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272
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94
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273
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95 main:
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96 jmp agent1
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272
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97
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273
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98 .data
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99 agent1_task:
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100 dd 0
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101 agent2_task:
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102 dd 0
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272
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103
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