因为比较常用的是 TCP 协议，所以在 opal/mca/btl/tcp/btl_tcp.h 头文件中找到对应的
struct mca_btl_tcp_component_t {
mca_btl_base_component_3_0_0_t super; /**< base BTL component */
uint32_t tcp_addr_count; /**< total number of addresses */
uint32_t tcp_num_btls; /**< number of interfaces available to the TCP component */
unsigned int tcp_num_links; /**< number of logical links per physical device */
struct mca_btl_tcp_module_t **tcp_btls; /**< array of available BTL modules */
int tcp_free_list_num; /**< initial size of free lists */
int tcp_free_list_max; /**< maximum size of free lists */
int tcp_free_list_inc; /**< number of elements to alloc when growing free lists */
int tcp_endpoint_cache; /**< amount of cache on each endpoint */
opal_proc_table_t tcp_procs; /**< hash table of tcp proc structures */
opal_mutex_t tcp_lock; /**< lock for accessing module state */
opal_list_t tcp_events;
opal_event_t tcp_recv_event; /**< recv event for IPv4 listen socket */
int tcp_listen_sd; /**< IPv4 listen socket for incoming connection requests */
unsigned short tcp_listen_port; /**< IPv4 listen port */
int tcp_port_min; /**< IPv4 minimum port */
int tcp_port_range; /**< IPv4 port range */
#if OPAL_ENABLE_IPV6
opal_event_t tcp6_recv_event; /**< recv event for IPv6 listen socket */
int tcp6_listen_sd; /**< IPv6 listen socket for incoming connection requests */
unsigned short tcp6_listen_port; /**< IPv6 listen port */
int tcp6_port_min; /**< IPv4 minimum port */
int tcp6_port_range; /**< IPv4 port range */
#endif
/* Port range restriction */
char* tcp_if_include; /**< comma seperated list of interface to include */
char* tcp_if_exclude; /**< comma seperated list of interface to exclude */
int tcp_sndbuf; /**< socket sndbuf size */
int tcp_rcvbuf; /**< socket rcvbuf size */
int tcp_disable_family; /**< disabled AF_family */
/* free list of fragment descriptors */
opal_free_list_t tcp_frag_eager;
opal_free_list_t tcp_frag_max;
opal_free_list_t tcp_frag_user;
int tcp_enable_progress_thread; /** Support for tcp progress thread flag */
opal_event_t tcp_recv_thread_async_event;
opal_mutex_t tcp_frag_eager_mutex;
opal_mutex_t tcp_frag_max_mutex;
opal_mutex_t tcp_frag_user_mutex;
/* Do we want to use TCP_NODELAY? */
int tcp_not_use_nodelay;
/* do we want to warn on all excluded interfaces
* that are not found?
*/
bool report_all_unfound_interfaces;
};
typedef struct mca_btl_tcp_component_t mca_btl_tcp_component_t;
OPAL_MODULE_DECLSPEC extern mca_btl_tcp_component_t mca_btl_tcp_component;这里有定义了一个TCP的组件，以及 TCP模块 (这里我就没有贴出来了)， 并且导出了这样一个变量。
接到上次说的话题，那么刚开始的时候，选择哪个通信协议呢？
通过在 PowerShell 下面搜索 findstr /SN "pml_recv" *.c， 并且 反复分析:
终于找到了对 mca_pml 进行赋值的函数体, 在 openmpi-3.0.1\ompi\mca\vprotocol\base\vprotocol_base_parasite.c 文件中:
int mca_vprotocol_base_parasite(void) {
if(mca_vprotocol.add_procs)
mca_pml.pml_add_procs = mca_vprotocol.add_procs;
if(mca_vprotocol.del_procs)
mca_pml.pml_del_procs = mca_vprotocol.del_procs;
if(mca_vprotocol.progress)
mca_pml.pml_progress = mca_vprotocol.progress;
if(mca_vprotocol.add_comm)
mca_pml.pml_add_comm = mca_vprotocol.add_comm;
if(mca_vprotocol.del_comm)
mca_pml.pml_del_comm = mca_vprotocol.del_comm;
if(mca_vprotocol.irecv_init)
mca_pml.pml_irecv_init = mca_vprotocol.irecv_init;
if(mca_vprotocol.irecv)
mca_pml.pml_irecv = mca_vprotocol.irecv;
if(mca_vprotocol.recv)
mca_pml.pml_recv = mca_vprotocol.recv;
if(mca_vprotocol.isend_init)
mca_pml.pml_isend_init = mca_vprotocol.isend_init;
if(mca_vprotocol.isend)
mca_pml.pml_isend = mca_vprotocol.isend;
if(mca_vprotocol.send)
mca_pml.pml_send = mca_vprotocol.send;
if(mca_vprotocol.iprobe)
mca_pml.pml_iprobe = mca_vprotocol.iprobe;
if(mca_vprotocol.probe)
mca_pml.pml_probe = mca_vprotocol.probe;
if(mca_vprotocol.start)
mca_pml.pml_start = mca_vprotocol.start;
if(mca_vprotocol.dump)
mca_pml.pml_dump = mca_vprotocol.dump;
if(mca_vprotocol.wait)
ompi_request_functions.req_wait = mca_vprotocol.wait;
if(mca_vprotocol.wait_all)
ompi_request_functions.req_wait_all = mca_vprotocol.wait_all;
if(mca_vprotocol.wait_any)
ompi_request_functions.req_wait_any = mca_vprotocol.wait_any;
if(mca_vprotocol.wait_some)
ompi_request_functions.req_wait_some = mca_vprotocol.wait_some;
if(mca_vprotocol.test)
ompi_request_functions.req_test = mca_vprotocol.test;
if(mca_vprotocol.test_all)
ompi_request_functions.req_test_all = mca_vprotocol.test_all;
if(mca_vprotocol.test_any)
ompi_request_functions.req_test_any = mca_vprotocol.test_any;
if(mca_vprotocol.test_some)
ompi_request_functions.req_test_some = mca_vprotocol.test_some;
return mca_vprotocol_base_request_parasite();
}这里对 mca_mpi 变量的每一个函数指针进行了赋值，让它选择对应的函数，也就是，我们选择什么协议，则依赖于 mca_vprotocol 这个变量了.
该变量在 vprotocol/base/base.h 头文件中声明的:
OMPI_DECLSPEC extern mca_vprotocol_base_module_t mca_vprotocol;我们在 vprotocol.h 头文件中看到 mca_vprotocol_base_module_t 这个结构体的声明:
typedef struct mca_vprotocol_base_module_2_0_0_t
{
/* PML module stuff */
mca_pml_base_module_add_procs_fn_t add_procs;
mca_pml_base_module_del_procs_fn_t del_procs;
mca_pml_base_module_enable_fn_t enable;
mca_pml_base_module_progress_fn_t progress;
mca_pml_base_module_add_comm_fn_t add_comm;
mca_pml_base_module_del_comm_fn_t del_comm;
mca_pml_base_module_irecv_init_fn_t irecv_init;
mca_pml_base_module_irecv_fn_t irecv;
mca_pml_base_module_recv_fn_t recv;
mca_pml_base_module_isend_init_fn_t isend_init;
mca_pml_base_module_isend_fn_t isend;
mca_pml_base_module_send_fn_t send;
mca_pml_base_module_iprobe_fn_t iprobe;
mca_pml_base_module_probe_fn_t probe;
mca_pml_base_module_start_fn_t start;
mca_pml_base_module_dump_fn_t dump;
/* Request wait/test stuff */
ompi_request_test_fn_t test;
ompi_request_test_any_fn_t test_any;
ompi_request_test_all_fn_t test_all;
ompi_request_test_some_fn_t test_some;
ompi_request_wait_fn_t wait;
ompi_request_wait_any_fn_t wait_any;
ompi_request_wait_all_fn_t wait_all;
ompi_request_wait_some_fn_t wait_some;
/* Custom requests classes to add extra data at end of pml requests */
opal_class_t * req_recv_class;
opal_class_t * req_send_class;
} mca_vprotocol_base_module_2_0_0_t;
typedef mca_vprotocol_base_module_2_0_0_t mca_vprotocol_base_module_t;根据局部性原理，观察到附近有一个函数 mca_vprotocol_base_select :
猜想它很可能是 选择可用协议 的函数， 于是在 linux 的 cscope 下直接跟进去，代码很长，但是很重要:
/*
* Function for selecting one component from all those that are
* available.
*
* Call the init function on all available components and get their
* priorities. Select the component with the highest priority. All
* other components will be closed and unloaded. The selected component
* will have all of its function pointers saved and returned to the
* caller.
*/
int mca_vprotocol_base_select(bool enable_progress_threads,
bool enable_mpi_threads)
{
int priority = 0, best_priority = -1;
opal_list_item_t *item = NULL;
mca_base_component_list_item_t *cli = NULL;
mca_vprotocol_base_component_t *component = NULL, *best_component = NULL;
mca_vprotocol_base_module_t *module = NULL, *best_module = NULL;
opal_list_t opened;
opened_component_t *om = NULL;
/* Traverse the list of available components; call their init
functions. */
OBJ_CONSTRUCT(&opened, opal_list_t);
OPAL_LIST_FOREACH(cli, &ompi_vprotocol_base_framework.framework_components, mca_base_component_list_item_t)
{
component = (mca_vprotocol_base_component_t *) cli->cli_component;
if (NULL == mca_vprotocol_base_include_list) {
continue;
}
V_OUTPUT_VERBOSE(500, "vprotocol select: initializing %s component %s", component->pmlm_version.mca_type_name, component->pmlm_version.mca_component_name);
if(strcmp(component->pmlm_version.mca_component_name,
mca_vprotocol_base_include_list)) {
V_OUTPUT_VERBOSE(500, "This component is not in the include list: skipping %s", component->pmlm_version.mca_component_name);
continue;
}
if(NULL == component->pmlm_init) {
V_OUTPUT_VERBOSE(2, "vprotocol select: no init function; ignoring component %s", component->pmlm_version.mca_component_name);
continue;
}
module = component->pmlm_init(&priority, enable_progress_threads, enable_mpi_threads);
if (NULL == module) {
V_OUTPUT_VERBOSE(2, "vprotocol select: init returned failure for component %s", component->pmlm_version.mca_component_name);
continue;
}
V_OUTPUT_VERBOSE(500, "vprotocol select: component %s init returned priority %d", component->pmlm_version.mca_component_name, priority);
if (priority > best_priority)
{
best_priority = priority;
best_component = component;
best_module = module;
}
om = (opened_component_t *) malloc(sizeof(opened_component_t));
if (NULL == om) return OMPI_ERR_OUT_OF_RESOURCE;
OBJ_CONSTRUCT(om, opal_list_item_t);
om->om_component = component;
opal_list_append(&opened, (opal_list_item_t*) om);
}
/* Finished querying all components. Check for the bozo case. */
if (NULL == best_component) {
V_OUTPUT_VERBOSE(2, "vprotocol select: no protocol has returned a positive priority, fault tolerance is OFF");
}
else
{
/* Save the winner */
mca_vprotocol_component = *best_component;
mca_vprotocol = *best_module;
}
/* Finalize all non-selected components */
for (item = opal_list_remove_first(&opened);
NULL != item;
item = opal_list_remove_first(&opened))
{
om = (opened_component_t *) item;
if (om->om_component != best_component) {
/* Finalize */
V_OUTPUT_VERBOSE(500, "vprotocol select: component %s not selected / finalized", om->om_component->pmlm_version.mca_component_name);
if (NULL != om->om_component->pmlm_finalize) {
/* Blatently ignore the return code (what would we do to
recover, anyway? This component is going away, so errors
don't matter anymore) */
om->om_component->pmlm_finalize();
}
}
OBJ_DESTRUCT(om);
free(om);
}
mca_base_components_close(mca_pml_v.output,
&ompi_vprotocol_base_framework.framework_components,
(mca_base_component_t *) best_component);
/* All done */
if(best_component != NULL)
{
V_OUTPUT_VERBOSE(500, "vprotocol select: component %s selected", mca_vprotocol_component.pmlm_version.mca_component_name);
return OMPI_SUCCESS;
}
else
return OMPI_ERR_NOT_FOUND;
} 大概思路就是有一个所有可用的通信协议组件的线性表，遍历地去初始化它们，然后得到对应的优先级，选择最高优先级的:
if (priority > best_priority)
{
best_priority = priority;
best_component = component;
best_module = module;
}那么随之而来就有一个问题了，这个优先级是怎么确定的呢？ 难道是通过不同网络协议的通信质量来决定不同的优先级吗？
仔细分析，得到优先级的一行源码在这里:
module = component->pmlm_init(&priority, enable_progress_threads, enable_mpi_threads);component这个变量 其实就是 mca_vprotocol_base_component_2_0_0_t 对应的该结构体，在vprotocol.h 中有定义:
typedef struct mca_vprotocol_base_component_2_0_0_t {
mca_base_component_t pmlm_version;
mca_base_component_data_t pmlm_data;
mca_vprotocol_base_component_init_fn_t pmlm_init;
mca_vprotocol_base_component_finalize_fn_t pmlm_finalize;
} mca_vprotocol_base_component_2_0_0_t;
typedef mca_vprotocol_base_component_2_0_0_t mca_vprotocol_base_component_t;那么，我们就该去看看 pmlm_init 这个函数是怎么得到优先级的。。。————下一篇。。
来源：oschina
链接：https://my.oschina.net/u/4329429/blog/3273815