Allow specifying a default signal iff epollsig has been explicitly requested

src/core/lib/iomgr/ev_epoll1_linux.c

@@ -676,7 +676,7 @@ static const grpc_event_engine_vtable vtable = {
 
 /* It is possible that GLIBC has epoll but the underlying kernel doesn't.
  * Create a dummy epoll_fd to make sure epoll support is available */
-const grpc_event_engine_vtable *grpc_init_epoll1_linux(void) {
+const grpc_event_engine_vtable *grpc_init_epoll1_linux(bool explicit_request) {
   if (!grpc_has_wakeup_fd()) {
     return NULL;
   }
@@ -703,6 +703,6 @@ const grpc_event_engine_vtable *grpc_init_epoll1_linux(void) {
 #include "src/core/lib/iomgr/ev_posix.h"
 /* If GRPC_LINUX_EPOLL is not defined, it means epoll is not available. Return
  * NULL */
-const grpc_event_engine_vtable *grpc_init_epoll1_linux(void) { return NULL; }
+const grpc_event_engine_vtable *grpc_init_epoll1_linux(bool explicit_request) { return NULL; }
 #endif /* defined(GRPC_POSIX_SOCKET) */
 #endif /* !defined(GRPC_LINUX_EPOLL) */

src/core/lib/iomgr/ev_epoll1_linux.h

@@ -39,6 +39,6 @@
 
 // a polling engine that utilizes a singleton epoll set and turnstile polling
 
-const grpc_event_engine_vtable *grpc_init_epoll1_linux(void);
+const grpc_event_engine_vtable *grpc_init_epoll1_linux(bool explicit_request);
 
 #endif /* GRPC_CORE_LIB_IOMGR_EV_EPOLL1_LINUX_H */

src/core/lib/iomgr/ev_epollsig_linux.c

@@ -1921,7 +1921,7 @@ static bool is_epoll_available() {
   return true;
 }
 
-const grpc_event_engine_vtable *grpc_init_epollsig_linux(void) {
+const grpc_event_engine_vtable *grpc_init_epollsig_linux(bool explicit_request) {
   /* If use of signals is disabled, we cannot use epoll engine*/
   if (is_grpc_wakeup_signal_initialized && grpc_wakeup_signal < 0) {
     return NULL;
@@ -1936,7 +1936,8 @@ const grpc_event_engine_vtable *grpc_init_epollsig_linux(void) {
   }
 
   if (!is_grpc_wakeup_signal_initialized) {
-    return NULL;
+    if (explicit_request) grpc_use_signal(SIGRTMIN + 6);    
+ else return NULL;
   }
 
   fd_global_init();
@@ -1958,7 +1959,7 @@ const grpc_event_engine_vtable *grpc_init_epollsig_linux(void) {
 #include "src/core/lib/iomgr/ev_posix.h"
 /* If GRPC_LINUX_EPOLL is not defined, it means epoll is not available. Return
  * NULL */
-const grpc_event_engine_vtable *grpc_init_epollsig_linux(void) { return NULL; }
+const grpc_event_engine_vtable *grpc_init_epollsig_linux(bool explicit_request) { return NULL; }
 #endif /* defined(GRPC_POSIX_SOCKET) */
 
 void grpc_use_signal(int signum) {}

src/core/lib/iomgr/ev_epollsig_linux.h

@@ -37,7 +37,7 @@
 #include "src/core/lib/iomgr/ev_posix.h"
 #include "src/core/lib/iomgr/port.h"
 
-const grpc_event_engine_vtable *grpc_init_epollsig_linux(void);
+const grpc_event_engine_vtable *grpc_init_epollsig_linux(bool explicit_request);
 
 #ifdef GRPC_LINUX_EPOLL
 void *grpc_fd_get_polling_island(grpc_fd *fd);

src/core/lib/iomgr/ev_poll_posix.c

@@ -1569,7 +1569,7 @@ static const grpc_event_engine_vtable vtable = {
     .shutdown_engine = shutdown_engine,
 };
 
-const grpc_event_engine_vtable *grpc_init_poll_posix(void) {
+const grpc_event_engine_vtable *grpc_init_poll_posix(bool explicit_request) {
   if (!grpc_has_wakeup_fd()) {
     return NULL;
   }
@@ -1579,7 +1579,7 @@ const grpc_event_engine_vtable *grpc_init_poll_posix(void) {
   return &vtable;
 }
 
-const grpc_event_engine_vtable *grpc_init_poll_cv_posix(void) {
+const grpc_event_engine_vtable *grpc_init_poll_cv_posix(bool explicit_request) {
   global_cv_fd_table_init();
   grpc_enable_cv_wakeup_fds(1);
   if (!GRPC_LOG_IF_ERROR("pollset_global_init", pollset_global_init())) {

src/core/lib/iomgr/ev_poll_posix.h

@@ -36,7 +36,7 @@
 
 #include "src/core/lib/iomgr/ev_posix.h"
 
-const grpc_event_engine_vtable *grpc_init_poll_posix(void);
-const grpc_event_engine_vtable *grpc_init_poll_cv_posix(void);
+const grpc_event_engine_vtable *grpc_init_poll_posix(bool explicit_request);
+const grpc_event_engine_vtable *grpc_init_poll_cv_posix(bool explicit_request);
 
 #endif /* GRPC_CORE_LIB_IOMGR_EV_POLL_POSIX_H */

src/core/lib/iomgr/ev_posix.c

@@ -58,7 +58,7 @@ grpc_wakeup_fd grpc_global_wakeup_fd;
 static const grpc_event_engine_vtable *g_event_engine;
 static const char *g_poll_strategy_name = NULL;
 
-typedef const grpc_event_engine_vtable *(*event_engine_factory_fn)(void);
+typedef const grpc_event_engine_vtable *(*event_engine_factory_fn)(bool explicit_request);
 
 typedef struct {
   const char *name;
@@ -104,7 +104,7 @@ static bool is(const char *want, const char *have) {
 static void try_engine(const char *engine) {
   for (size_t i = 0; i < GPR_ARRAY_SIZE(g_factories); i++) {
     if (is(engine, g_factories[i].name)) {
-      if ((g_event_engine = g_factories[i].factory())) {
+      if ((g_event_engine = g_factories[i].factory(0 == strcmp(engine, g_factories[i].name)))) {
         g_poll_strategy_name = g_factories[i].name;
         gpr_log(GPR_DEBUG, "Using polling engine: %s", g_factories[i].name);
         return;