commit 4eb910e82ed26a7193f9a70ab03a37184aa495f9
author Yurii Zubrytskyi <zyy@google.com> Wed Mar 18 22:29:10 2020 -0700
committer Yurii Zubrytskyi <zyy@google.com> Tue Mar 24 10:28:08 2020 -0700
tree f793b6b225c10b7ff218649177294b088cf0ed9a
parent 2488c21d8bb8b4e58b6b482ad1167c97cbd859e1

[adb] Optimize fdevent machinery

- Use one fewer heap allocation per fdevent object
- Lazy-init the fdevent context

Bug: 151239696
Test: various adb commands on Win/Linux

Change-Id: Ic7de207b30495e618f187e097c0276ad42c34005
Merged-In: Ic7de207b30495e618f187e097c0276ad42c34005

adb/fdevent/fdevent.cpp

diff --git a/adb/fdevent/fdevent.cpp b/adb/fdevent/fdevent.cpp
index 562f587..fd55020 100644
--- a/adb/fdevent/fdevent.cpp
+++ b/adb/fdevent/fdevent.cpp
@@ -63,7 +63,10 @@
 
     int fd_num = fd.get();
 
-    fdevent* fde = new fdevent();
+    auto [it, inserted] = this->installed_fdevents_.emplace(fd_num, fdevent{});
+    CHECK(inserted);
+
+    fdevent* fde = &it->second;
     fde->id = fdevent_id_++;
     fde->state = 0;
     fde->fd = std::move(fd);
@@ -76,10 +79,6 @@
         LOG(ERROR) << "failed to set non-blocking mode for fd " << fde->fd.get();
     }
 
-    auto [it, inserted] = this->installed_fdevents_.emplace(fd_num, fde);
-    CHECK(inserted);
-    UNUSED(it);
-
     this->Register(fde);
     return fde;
 }
@@ -92,12 +91,12 @@
 
     this->Unregister(fde);
 
-    auto erased = this->installed_fdevents_.erase(fde->fd.get());
+    unique_fd fd = std::move(fde->fd);
+
+    auto erased = this->installed_fdevents_.erase(fd.get());
     CHECK_EQ(1UL, erased);
 
-    unique_fd result = std::move(fde->fd);
-    delete fde;
-    return result;
+    return fd;
 }
 
 void fdevent_context::Add(fdevent* fde, unsigned events) {
@@ -123,9 +122,9 @@
 
     for (const auto& [fd, fde] : this->installed_fdevents_) {
         UNUSED(fd);
-        auto timeout_opt = fde->timeout;
+        auto timeout_opt = fde.timeout;
         if (timeout_opt) {
-            auto deadline = fde->last_active + *timeout_opt;
+            auto deadline = fde.last_active + *timeout_opt;
             auto time_left = duration_cast<std::chrono::milliseconds>(deadline - now);
             if (time_left < 0ms) {
                 time_left = 0ms;
@@ -194,11 +193,13 @@
 #endif
 }
 
-static auto& g_ambient_fdevent_context =
-        *new std::unique_ptr<fdevent_context>(fdevent_create_context());
+static auto& g_ambient_fdevent_context() {
+    static auto context = fdevent_create_context().release();
+    return context;
+}
 
 static fdevent_context* fdevent_get_ambient() {
-    return g_ambient_fdevent_context.get();
+    return g_ambient_fdevent_context();
 }
 
 fdevent* fdevent_create(int fd, fd_func func, void* arg) {
@@ -256,5 +257,6 @@
 }
 
 void fdevent_reset() {
-    g_ambient_fdevent_context = fdevent_create_context();
+    auto old = std::exchange(g_ambient_fdevent_context(), fdevent_create_context().release());
+    delete old;
 }