Let's look at our multithreaded resource manager example in more detail:
#include <errno.h> #include <stdio.h> #include <stddef.h> #include <stdlib.h> #include <unistd.h> #include <string.h> /* * Define THREAD_POOL_PARAM_T such that we can avoid a compiler * warning when we use the dispatch_*() functions below */ #define THREAD_POOL_PARAM_T dispatch_context_t #include <sys/iofunc.h> #include <sys/dispatch.h> static resmgr_connect_funcs_t connect_funcs; static resmgr_io_funcs_t io_funcs; static iofunc_attr_t attr; int main(int argc, char **argv) { /* declare variables we'll be using */ thread_pool_attr_t pool_attr; resmgr_attr_t resmgr_attr; dispatch_t *dpp; thread_pool_t *tpp; int id; /* initialize dispatch interface */ if((dpp = dispatch_create()) == NULL) { fprintf(stderr, "%s: Unable to allocate dispatch handle.\n", argv[0]); return EXIT_FAILURE; } /* initialize resource manager attributes */ memset(&resmgr_attr, 0, sizeof resmgr_attr); resmgr_attr.nparts_max = 1; resmgr_attr.msg_max_size = 2048; /* initialize functions for handling messages */ iofunc_func_init(_RESMGR_CONNECT_NFUNCS, &connect_funcs, _RESMGR_IO_NFUNCS, &io_funcs); /* initialize attribute structure used by the device */ iofunc_attr_init(&attr, S_IFNAM | 0666, 0, 0); /* attach our device name */ id = resmgr_attach(dpp, /* dispatch handle */ &resmgr_attr, /* resource manager attrs */ "/dev/sample", /* device name */ _FTYPE_ANY, /* open type */ 0, /* flags */ &connect_funcs, /* connect routines */ &io_funcs, /* I/O routines */ &attr); /* handle */ if(id == -1) { fprintf(stderr, "%s: Unable to attach name.\n", argv[0]); return EXIT_FAILURE; } /* initialize thread pool attributes */ memset(&pool_attr, 0, sizeof pool_attr); pool_attr.handle = dpp; pool_attr.context_alloc = dispatch_context_alloc; pool_attr.block_func = dispatch_block; pool_attr.unblock_func = dispatch_unblock; pool_attr.handler_func = dispatch_handler; pool_attr.context_free = dispatch_context_free; pool_attr.lo_water = 2; pool_attr.hi_water = 4; pool_attr.increment = 1; pool_attr.maximum = 50; /* allocate a thread pool handle */ if((tpp = thread_pool_create(&pool_attr, POOL_FLAG_EXIT_SELF)) == NULL) { fprintf(stderr, "%s: Unable to initialize thread pool.\n", argv[0]); return EXIT_FAILURE; } /* Start the threads. This function doesn't return. */ thread_pool_start(tpp); return EXIT_SUCCESS; }
The thread pool attribute (pool_attr) controls various aspects of the thread pool, such as which functions get called when a new thread is started or dies, the total number of worker threads, the minimum number, and so on.