unix, windows: add uv_loop_configure() function

The only supported option right now is UV_LOOP_BLOCK_SIGNAL, which only
supports the SIGPROF signal and only on UNIX platforms.  So yes, it is
kind of limited right now.  But everything has to start somewhere.

Refs strongloop/strong-agent#3 and strongloop-internal/scrum-cs#37.

PR-URL: https://github.com/libuv/libuv/pull/15
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>

include/uv.h

@@ -226,6 +226,16 @@ typedef struct uv_work_s uv_work_t;
 typedef struct uv_cpu_info_s uv_cpu_info_t;
 typedef struct uv_interface_address_s uv_interface_address_t;
 
+typedef enum {
+  /* Block a signal when polling for new events.  The second argument to
+   * uv_loop_configure() is the signal number.
+   *
+   * This operation is currently only implemented for SIGPROF signals,
+   * to suppress unnecessary wakeups when using a sampling profiler.
+   * Requesting other signals will fail with UV_EINVAL.
+   */
+  UV_LOOP_BLOCK_SIGNAL
+} uv_loop_option;
 
 typedef enum {
   UV_RUN_DEFAULT = 0,
@@ -264,6 +274,15 @@ UV_EXTERN void uv_loop_delete(uv_loop_t*);
  */
 UV_EXTERN uv_loop_t* uv_default_loop(void);
 
+/*
+ * Set additional loop options.  You should normally call this before the
+ * first call to uv_run() unless mentioned otherwise.
+ *
+ * Returns 0 on success or a UV_E* error code on failure.  Be prepared to
+ * handle UV_ENOSYS; it means the loop option is not supported by the platform.
+ */
+UV_EXTERN int uv_loop_configure(uv_loop_t* loop, uv_loop_option option, ...);
+
 /*
  * This function runs the event loop. It will act differently depending on the
  * specified mode:

src/unix/loop.c

@@ -112,3 +112,15 @@ void uv__loop_delete(uv_loop_t* loop) {
   loop->watchers = NULL;
   loop->nwatchers = 0;
 }
+
+
+int uv__loop_configure(uv_loop_t* loop, uv_loop_option option, va_list ap) {
+  if (option != UV_LOOP_BLOCK_SIGNAL)
+    return UV_ENOSYS;
+
+  if (va_arg(ap, int) != SIGPROF)
+    return UV_EINVAL;
+
+  loop->flags |= UV_LOOP_BLOCK_SIGPROF;
+  return 0;
+}

src/uv-common.c

@@ -24,6 +24,7 @@
 
 #include <stdio.h>
 #include <assert.h>
+#include <stdarg.h>
 #include <stddef.h> /* NULL */
 #include <stdlib.h> /* malloc */
 #include <string.h> /* memset */
@@ -434,3 +435,16 @@ void uv_stop(uv_loop_t* loop) {
 uint64_t uv_now(uv_loop_t* loop) {
   return loop->time;
 }
+
+
+int uv_loop_configure(uv_loop_t* loop, uv_loop_option option, ...) {
+  va_list ap;
+  int err;
+
+  va_start(ap, option);
+  /* Any platform-agnostic options should be handled here. */
+  err = uv__loop_configure(loop, option, ap);
+  va_end(ap);
+
+  return err;
+}

src/uv-common.h

@@ -28,6 +28,7 @@
 #define UV_COMMON_H_
 
 #include <assert.h>
+#include <stdarg.h>
 #include <stddef.h>
 
 #if defined(_MSC_VER) && _MSC_VER < 1600
@@ -77,6 +78,7 @@ int uv__set_artificial_error(uv_loop_t* loop, uv_err_code code);
 uv_err_t uv__new_sys_error(int sys_error);
 uv_err_t uv__new_artificial_error(uv_err_code code);
 
+int uv__loop_configure(uv_loop_t* loop, uv_loop_option option, va_list ap);
 int uv__tcp_bind(uv_tcp_t* handle, struct sockaddr_in addr);
 int uv__tcp_bind6(uv_tcp_t* handle, struct sockaddr_in6 addr);
 

src/win/core.c

@@ -174,6 +174,11 @@ void uv_loop_delete(uv_loop_t* loop) {
 }
 
 
+int uv__loop_configure(uv_loop_t* loop, uv_loop_option option, va_list ap) {
+  return UV_ENOSYS;
+}
+
+
 int uv_backend_fd(const uv_loop_t* loop) {
   return -1;
 }