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Module:

antithread

Summary:

Accelerated Native Technology Implementation of "threads"

Author:

Rusty Russell <rusty@rustcorp.com.au>

Dependencies:

 ccan/antithread/alloc ccan/err ccan/list ccan/noerr ccan/read_write_all ccan/talloc  

Description:

On systems with multiple CPUs, it's often faster to split work across different execution units. Under Unix-like systems, the two methods of doing this are (POSIX) threads or processes.

Threads have the disadvantage that they share all of the address space: using software instead of hardware isolation (eg. for malloc) is inefficient and less secure. Various subtle errors can occur because programmers in one part of the code do not expect concurrency.

Processes have the disadvantage that there is no common infrastructure for sharing memory: without this, programmers are faced with the unpalatable options of using slower options or creating their own infrastructure.

The antithread module provides memory-sharing infrastructure: the programmer indicates the size of the memory to share, and then creates subprocesses which share the memory. Pipes are used to hand pointers between the main process and the children: usually pointers into the shared memory.

Example:

#include <ccan/antithread/antithread.h>
#include <ccan/talloc/talloc.h>
#include <ctype.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

// Silly example: child makes rot13 copy.
static void *rot13(struct at_pool *pool, void *unused)
{
        char *r, *p;
        while ((r = at_read_parent(pool)) != NULL) {
                unsigned int i;
                // r is inside pool, so talloc off it is also inside.
                p = talloc_array(r, char, strlen(r) + 1);
                for (i = 0; r[i]; i++) {
                        if (!isalpha(r[i]))
                                p[i] = r[i];
                        else if (toupper(r[i]) < 'N')
                                p[i] = r[i] + 13;
                        else
                                p[i] = r[i] - 13;
                }
                // Tell parent about our copy.
                at_tell_parent(pool, p);
        }
        return NULL;
}

#define NUM_CHILDREN 4

int main(int argc, char *argv[])
{
        struct at_pool *pool;
        struct athread *child[NUM_CHILDREN];
        unsigned int i;

        // Create pool and some children
        pool = at_pool(1024*1024);
        for (i = 0; i < NUM_CHILDREN; i++)
                child[i] = at_run(pool, rot13, NULL);

        // Pass out work to children.
        for (i = 1; i < argc; i++)
                at_tell(child[i % NUM_CHILDREN],
                        talloc_strdup(at_pool_ctx(pool), argv[i]));

        // Read back results.
        for (i = 1; i < argc; i++)
                printf("%s ", (char *)at_read(child[i % NUM_CHILDREN]));
        printf("\n");

        // Freeing pool kills children, too.
        talloc_free(pool);
        return 0;
}

License:

GPL (v3 or any later version)