|
| 1 | +/* |
| 2 | +output 1 - 100 |
| 3 | +two threads, one prints odd one prints even in order |
| 4 | +*/ |
| 5 | + |
| 6 | +#include <stdio.h> |
| 7 | +#include <stdlib.h> |
| 8 | +#include <pthread.h> |
| 9 | + |
| 10 | +#define START_NUMBER 1 |
| 11 | +#define END_NUMBER 100 |
| 12 | + |
| 13 | +pthread_mutex_t mtx; |
| 14 | +pthread_cond_t cond; |
| 15 | + |
| 16 | +int seq; |
| 17 | +int run_thread; |
| 18 | + |
| 19 | +typedef struct range_s { |
| 20 | + int start; |
| 21 | + int end; |
| 22 | +} range_t; |
| 23 | + |
| 24 | +int odd_print_one(const int start, const int end) { |
| 25 | + int rc = 0; |
| 26 | + |
| 27 | + pthread_mutex_lock(&mtx); |
| 28 | + |
| 29 | + // wait for cond to be singaled by using mtx and cond |
| 30 | + while (run_thread != 1) { |
| 31 | + pthread_cond_wait(&cond, &mtx); |
| 32 | + } |
| 33 | + if (seq > end) { |
| 34 | + rc = -1; |
| 35 | + } else { |
| 36 | + printf("%d ", seq); |
| 37 | + seq ++; |
| 38 | + } |
| 39 | + run_thread = 2; |
| 40 | + |
| 41 | + // siganl cond variable; |
| 42 | + pthread_cond_signal(&cond); |
| 43 | + pthread_mutex_unlock(&mtx); |
| 44 | + |
| 45 | + return rc; |
| 46 | +} |
| 47 | + |
| 48 | +/* most of code is common with odd_print_one(), they can be |
| 49 | + incooperated as one function, for readability, I keep them |
| 50 | + separated here. */ |
| 51 | +int even_print_one(const int start, const int end) { |
| 52 | + int rc = 0; |
| 53 | + pthread_mutex_lock(&mtx); |
| 54 | + |
| 55 | + // wait for cond to be singaled by using mtx and cond |
| 56 | + while (run_thread != 2) { |
| 57 | + pthread_cond_wait(&cond, &mtx); |
| 58 | + } |
| 59 | + if (seq > end) { |
| 60 | + rc = -1; |
| 61 | + } else { |
| 62 | + printf("%d ", seq); |
| 63 | + seq ++; |
| 64 | + } |
| 65 | + run_thread = 1; |
| 66 | + |
| 67 | + // siganl cond variable |
| 68 | + pthread_mutex_unlock(&mtx); |
| 69 | + pthread_cond_signal(&cond); |
| 70 | + |
| 71 | + return rc; |
| 72 | +} |
| 73 | + |
| 74 | +void *odd_printer(void *args) { |
| 75 | + int rc; |
| 76 | + const int start = ((range_t *)args)->start; |
| 77 | + const int end = ((range_t *)args)->end; |
| 78 | + do { |
| 79 | + rc = odd_print_one(start, end); |
| 80 | + } while (rc == 0); |
| 81 | + |
| 82 | + return NULL; |
| 83 | +} |
| 84 | + |
| 85 | +void *even_printer(void *args) { |
| 86 | + int rc; |
| 87 | + const int start = ((range_t *)args)->start; |
| 88 | + const int end = ((range_t *)args)->end; |
| 89 | + do { |
| 90 | + rc = even_print_one(start, end); |
| 91 | + } while(rc == 0); |
| 92 | + |
| 93 | + return NULL; |
| 94 | +} |
| 95 | + |
| 96 | +int main() { |
| 97 | + pthread_t odd_thread, even_thread; |
| 98 | + int rc; |
| 99 | + void *ret; |
| 100 | + |
| 101 | + const range_t range = {START_NUMBER, END_NUMBER}; |
| 102 | + |
| 103 | + seq = range.start; |
| 104 | + run_thread = 1; |
| 105 | + |
| 106 | + pthread_mutex_init(&mtx, NULL); |
| 107 | + pthread_cond_init(&cond, NULL); |
| 108 | + |
| 109 | + rc = pthread_create(&odd_thread, NULL, odd_printer, (void *)&range); |
| 110 | + if (rc != 0) { |
| 111 | + goto cu1; |
| 112 | + } |
| 113 | + rc = pthread_create(&even_thread, NULL, even_printer, (void *)&range); |
| 114 | + if (rc != 0) { |
| 115 | + pthread_kill(odd_thread, 0); |
| 116 | + goto cu0; |
| 117 | + } |
| 118 | + |
| 119 | + // clean up |
| 120 | + pthread_join(even_thread, &ret); |
| 121 | +cu0: |
| 122 | + pthread_join(odd_thread, &ret); |
| 123 | + |
| 124 | +cu1: |
| 125 | + printf("\n"); |
| 126 | + pthread_mutex_destroy(&mtx); |
| 127 | + pthread_cond_destroy(&cond); |
| 128 | + |
| 129 | + return rc; |
| 130 | +} |
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