Refactor Evented::Arena to allocate in blocks [fixup #14996] (#15205)

Replaces the static `mmap` that must accommodate for as many file descriptors as allowed by ulimit/rlimit. Despite being virtual memory, not really allocated in practice, this led to out-of-memory errors in some situations. The arena now dynamically allocates individual blocks as needed (no more virtual memory). For simplicity reasons it will only ever grow, and won't shrink (we may think of a solution for this later). The original safety guarantees still hold: once an entry has been allocated in the arena, its pointer won't change. The event loop still limits the arena capacity to the hardware limit (ulimit: open files). **Side effect:** the arena don't need to remember the maximum fd/index anymore; that was only needed for `fork`; we can simply iterate the allocated blocks now. Co-authored-by: Johannes Müller <[email protected]>
crystal-lang · Nov 21, 2024 · 02df7ff · 02df7ff
1 parent d57c9d8
commit 02df7ff
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Showing 5 changed files with 122 additions and 99 deletions.
diff --git a/spec/std/crystal/evented/arena_spec.cr b/spec/std/crystal/evented/arena_spec.cr
@@ -5,7 +5,7 @@ require "spec"
 describe Crystal::Evented::Arena do
   describe "#allocate_at?" do
     it "yields block when not allocated" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       pointer = nil
       index = nil
       called = 0
@@ -31,7 +31,7 @@ describe Crystal::Evented::Arena do
     end
 
     it "allocates up to capacity" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       indexes = [] of Crystal::Evented::Arena::Index
 
       indexes = 32.times.map do |i|
@@ -49,15 +49,15 @@ describe Crystal::Evented::Arena do
     end
 
     it "checks bounds" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       expect_raises(IndexError) { arena.allocate_at?(-1) { } }
       expect_raises(IndexError) { arena.allocate_at?(33) { } }
     end
   end
 
   describe "#get" do
     it "returns previously allocated object" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       pointer = nil
 
       index = arena.allocate_at(30) do |ptr|
@@ -77,15 +77,15 @@ describe Crystal::Evented::Arena do
     end
 
     it "can't access unallocated object" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
 
       expect_raises(RuntimeError) do
         arena.get(Crystal::Evented::Arena::Index.new(10, 0)) { }
       end
     end
 
     it "checks generation" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       called = 0
 
       index1 = arena.allocate_at(2) { called += 1 }
@@ -102,15 +102,15 @@ describe Crystal::Evented::Arena do
     end
 
     it "checks out of bounds" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       expect_raises(IndexError) { arena.get(Crystal::Evented::Arena::Index.new(-1, 0)) { } }
       expect_raises(IndexError) { arena.get(Crystal::Evented::Arena::Index.new(33, 0)) { } }
     end
   end
 
   describe "#get?" do
     it "returns previously allocated object" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       pointer = nil
 
       index = arena.allocate_at(30) do |ptr|
@@ -131,7 +131,7 @@ describe Crystal::Evented::Arena do
     end
 
     it "can't access unallocated index" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
 
       called = 0
       ret = arena.get?(Crystal::Evented::Arena::Index.new(10, 0)) { called += 1 }
@@ -140,7 +140,7 @@ describe Crystal::Evented::Arena do
     end
 
     it "checks generation" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       called = 0
 
       old_index = arena.allocate_at(2) { }
@@ -166,7 +166,7 @@ describe Crystal::Evented::Arena do
     end
 
     it "checks out of bounds" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       called = 0
 
       arena.get?(Crystal::Evented::Arena::Index.new(-1, 0)) { called += 1 }.should be_false
@@ -178,7 +178,7 @@ describe Crystal::Evented::Arena do
 
   describe "#free" do
     it "deallocates the object" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
 
       index1 = arena.allocate_at(3) { |ptr| ptr.value = 123 }
       arena.free(index1) { }
@@ -192,7 +192,7 @@ describe Crystal::Evented::Arena do
     end
 
     it "checks generation" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
 
       called = 0
       old_index = arena.allocate_at(1) { }
@@ -214,7 +214,7 @@ describe Crystal::Evented::Arena do
     end
 
     it "checks out of bounds" do
-      arena = Crystal::Evented::Arena(Int32).new(32)
+      arena = Crystal::Evented::Arena(Int32, 96).new(32)
       called = 0
 
       arena.free(Crystal::Evented::Arena::Index.new(-1, 0)) { called += 1 }
@@ -223,4 +223,32 @@ describe Crystal::Evented::Arena do
       called.should eq(0)
     end
   end
+
+  it "#each_index" do
+    arena = Crystal::Evented::Arena(Int32, 96).new(32)
+    indices = [] of {Int32, Crystal::Evented::Arena::Index}
+
+    arena.each_index { |i, index| indices << {i, index} }
+    indices.should be_empty
+
+    index5 = arena.allocate_at(5) { }
+
+    arena.each_index { |i, index| indices << {i, index} }
+    indices.should eq([{5, index5}])
+
+    index3 = arena.allocate_at(3) { }
+    index11 = arena.allocate_at(11) { }
+    index10 = arena.allocate_at(10) { }
+    index30 = arena.allocate_at(30) { }
+
+    indices.clear
+    arena.each_index { |i, index| indices << {i, index} }
+    indices.should eq([
+      {3, index3},
+      {5, index5},
+      {10, index10},
+      {11, index11},
+      {30, index30},
+    ])
+  end
 end
diff --git a/src/crystal/system/unix/epoll/event_loop.cr b/src/crystal/system/unix/epoll/event_loop.cr
@@ -50,7 +50,7 @@ class Crystal::Epoll::EventLoop < Crystal::Evented::EventLoop
       system_set_timer(@timers.next_ready?)
 
       # re-add all registered fds
-      Evented.arena.each { |fd, index| system_add(fd, index) }
+      Evented.arena.each_index { |fd, index| system_add(fd, index) }
     end
   {% end %}