Allow external TaskQueue implementations on Linux

webrtc/rtc_base/BUILD.gn

Index: webrtc/rtc_base/BUILD.gn
diff --git a/webrtc/rtc_base/BUILD.gn b/webrtc/rtc_base/BUILD.gn
index 60d1f57583cf9f86f0d74ac6c63484d30a5f39c6..474e06c898898a55147f6e01ac2f7e2d049c08b6 100644
--- a/webrtc/rtc_base/BUILD.gn
+++ b/webrtc/rtc_base/BUILD.gn
@@ -294,42 +294,65 @@ config("enable_libevent_config") {
   defines = [ "WEBRTC_BUILD_LIBEVENT" ]
 }
 
-rtc_static_library("rtc_task_queue") {
+rtc_source_set("rtc_task_queue") {
   public_deps = [
     ":rtc_base_approved",
+    ":rtc_task_queue_api",
   ]
 
+  if (rtc_link_task_queue_impl) {
+    deps = [
+      ":rtc_task_queue_impl",
+    ]
+  }
+}

[kwiberg-webrtc, 2017/08/23 13:23:26]

I think it would be better to not have this target, and instead have all TQ
users depend on _api. That way, our test targets can unconditionally depend on
_impl, and our library target(s) can depend on _impl if rtc_link_task_queue_impl
is true. (See the long comment in another file where I expand on this.)

+
+rtc_source_set("rtc_task_queue_api") {

[kwiberg-webrtc, 2017/08/23 13:23:26]

Note in a comment that anyone who uses this needs to link with a TQ
implementation? The normal convention is that build targets have dependencies on
everything they need, and this one is an exception to that rule.

   if (build_with_chromium) {
     sources = [
-      "../../webrtc_overrides/webrtc/rtc_base/task_queue.cc",
       "../../webrtc_overrides/webrtc/rtc_base/task_queue.h",
     ]
   } else {
     sources = [
       "task_queue.h",
-      "task_queue_posix.h",
     ]
+  }
+  deps = [
+    ":rtc_base_approved",
+  ]
+}
+
+rtc_source_set("rtc_task_queue_impl") {

[kwiberg-webrtc, 2017/08/23 13:23:26]

Excellent with the _api and _impl targets. Things are split between them just
like I would want.

+  deps = [
+    ":rtc_base_approved",
+    ":rtc_task_queue_api",
+  ]
+  if (build_with_chromium) {
+    sources = [
+      "../../webrtc_overrides/webrtc/rtc_base/task_queue.cc",
+    ]
+  } else {
     if (rtc_build_libevent) {
-      deps = [
-        "//base/third_party/libevent",
-      ]
+      deps += [ "//base/third_party/libevent" ]
     }
-
     if (rtc_enable_libevent) {
-      sources += [
+      sources = [
         "task_queue_libevent.cc",
         "task_queue_posix.cc",
+        "task_queue_posix.h",
       ]
       all_dependent_configs = [ ":enable_libevent_config" ]
     } else {
       if (is_mac || is_ios) {
-        sources += [
+        sources = [
           "task_queue_gcd.cc",
           "task_queue_posix.cc",
         ]
       }
       if (is_win) {
-        sources += [ "task_queue_win.cc" ]
+        sources = [
+          "task_queue_win.cc",
+        ]
       }
     }
   }