使用线程生成随机数
使用线程生成随机数
提问于 2020-11-17 06:38:31
我尝试生成一个介于-1和+1之间的随机浮点数，总数由用户指定，以及线程的数量，然后随机数的总量在线程之间平均分配，线程都使用一个工作区结构。
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
typedef struct WorkspaceStruct {
unsigned int tid;
int points_generated;
int points_in_circle;
unsigned int seed;
}Workspace;
void *worker(void *ws) {
Workspace *workspace = (Workspace *) ws; // link worker to workspace
pthread_mutex_lock(&mutex);
printf("Worker %d\n", workspace->tid);
int max = workspace->points_generated;
unsigned int seed = workspace->seed;
for (int i = 0; i < max; ++i) {
float point_x = (float)rand_r(&seed) / RAND_MAX * 2.0 - 1.0;
float point_y = (float)rand_r(&seed) / RAND_MAX * 2.0 - 1.0;
printf("x: %f, y: %f\n", point_x, point_y);
}
pthread_mutex_unlock(&mutex);
pthread_exit(NULL);
}
void calculate_circle_area(int total_samples, int no_workers) {
pthread_t worker_thread[no_workers];
Workspace workspace;
workspace.points_generated = total_samples / no_workers;
workspace.tid = 0;
workspace.seed = time(0);
for (int i = 0; i < no_workers; ++i) {
workspace.tid += 1;
pthread_create(&worker_thread[i], NULL, worker, &workspace);
pthread_join(worker_thread[i], NULL);
}
}
int main(int argc, char *argv[]) {
if (argc < 3) {
printf("usage: ./program [no. of samples] [no. of worker threads]\n");
return EXIT_FAILURE;
} else {
int total_samples = atoi(argv[1]);
int no_workers = atoi(argv[2]);
printf("\n");
calculate_circle_area(total_samples, no_workers);
printf("\n");
return EXIT_SUCCESS;
}
}这在很大程度上是有效的，它确实生成了随机数，并且一切都被正确地拆分，但是每个线程生成相同的数，但是线程中的每个数是不同的。
命令的输出示例：./calc_area 9 3(总共生成9个随机数，使用3个线程)
Worker 1
x: 0.506291, y: -0.765927
x: -0.941786, y: -0.598265
x: 0.962658, y: -0.609824
Worker 2
x: 0.506291, y: -0.765927
x: -0.941786, y: -0.598265
x: 0.962658, y: -0.609824
Worker 3
x: 0.506291, y: -0.765927
x: -0.941786, y: -0.598265
x: 0.962658, y: -0.609824我想让每个线程相互生成不同的数字，我该怎么做呢？谢谢
回答 1
Stack Overflow用户
发布于 2020-11-17 08:14:54
由于您包含了多线程标记，因此这里有一个使用Ada的解决方案。在这种情况下，随机数种子由每个任务(即线程)重置，确保种子不同，因此随机数序列也不同。
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Numerics.Float_Random; use Ada.Numerics.Float_Random;
with Ada.Float_Text_IO; use Ada.Float_Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
procedure Main is
type Point is record
X : Float;
Y : Float;
end record;
procedure Print (Item : Point) is
begin
Put ("X:");
Put (Item => Item.X, Fore => 2, Aft => 4, Exp => 0);
Put (" Y:");
Put (Item => Item.Y, Fore => 2, Aft => 4, Exp => 0);
New_Line;
end Print;
type Point_Array is array (Positive range <>) of Point;
task type worker is
entry Set_Num (Count : Positive);
entry Report;
end worker;
task body worker is
Seed : Generator;
Num_Points : Positive;
begin
Reset (Seed);
accept Set_Num (Count : Positive) do
Num_Points := Count;
end Set_Num;
declare
Buf : Point_Array (1 .. Num_Points);
begin
for I in Buf'Range loop
Buf (I).X := Random (Seed) * 2.0 - 1.0;
Buf (I).Y := Random (Seed) * 2.0 - 1.0;
end loop;
accept Report;
for I in Buf'Range loop
Print (Buf (I));
end loop;
New_Line;
end;
end worker;
type Team is array (Positive range <>) of worker;
Num_Tasks : Positive;
Num_Rand : Positive;
begin
Put ("Enter the number of task: ");
Get (Num_Tasks);
Put ("Enter the number of results per task: ");
Get (Num_Rand);
declare
Workers : Team (1 .. Num_Tasks);
begin
for I in Workers'Range loop
Workers (I).Set_Num (Num_Rand);
end loop;
for I in Workers'range loop
Put_Line ("Worker" & I'Image);
Workers (I).Report;
delay 0.01;
end loop;
end;
end Main;使用6个任务和每个任务4个结果的执行的输出为：
Enter the number of task: 6
Enter the number of results per task: 4
Worker 1
X: 0.7487 Y:-0.6497
X:-0.9634 Y: 0.6317
X:-0.9189 Y: 0.8070
X: 0.8837 Y:-0.3839
Worker 2
X: 0.6409 Y:-0.4913
X:-0.0185 Y: 0.1078
X:-0.6408 Y:-0.9719
X:-0.6199 Y: 0.9301
Worker 3
X:-0.9440 Y: 0.1089
X:-0.1354 Y:-0.3133
X: 0.8479 Y:-0.7389
X: 0.8399 Y: 0.4826
Worker 4
X:-0.9165 Y:-0.3652
X: 0.4137 Y:-0.6292
X: 0.6467 Y: 0.9344
X: 0.2898 Y: 0.1059
Worker 5
X: 0.8818 Y:-0.3551
X:-0.5161 Y:-0.5251
X:-0.6831 Y:-0.0531
X: 0.8207 Y:-0.7419
Worker 6
X: 0.2529 Y:-0.9385
X: 0.5640 Y: 0.3365
X:-0.4477 Y: 0.1642
X: 0.8230 Y: 0.8284页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/64866748
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