fix: proactor_threads is respected in k8s

Author: starek4

src/server/dfly_main.cc

@@ -82,6 +82,7 @@ ABSL_DECLARE_FLAG(uint32_t, memcached_port);
 ABSL_DECLARE_FLAG(uint16_t, admin_port);
 ABSL_DECLARE_FLAG(std::string, admin_bind);
 ABSL_DECLARE_FLAG(strings::MemoryBytesFlag, maxmemory);
+ABSL_DECLARE_FLAG(uint32_t, proactor_threads);
 
 ABSL_FLAG(string, bind, "",
           "Bind address. If empty - binds on all interfaces. "
@@ -1080,6 +1081,12 @@ Usage: dragonfly [FLAGS]
 
 #ifdef __linux__
   UpdateResourceLimitsIfInsideContainer(&mem_info, &max_available_threads);
+  // If --proactor_threads (or DFLY_proactor_threads env var) was explicitly set by the user,
+  // honor it over the cgroup-derived CPU limit. The flag defaults to 0, so any non-zero value
+  // means the user explicitly requested a specific thread count.
+  if (absl::GetFlag(FLAGS_proactor_threads) > 0) {
+    max_available_threads = 0;  // causes ProactorPool to use FLAGS_proactor_threads
+  }
 #endif
 
   if (mem_info.swap_total != 0)

tests/dragonfly/proactor_threads_test.py

@@ -0,0 +1,68 @@
+"""
+Tests that --proactor_threads is respected even inside containers with CPU limits.
+
+Background: UpdateResourceLimitsIfInsideContainer() reads the cgroup CPU quota and
+passes it as pool_size to ProactorPool. When pool_size != 0, helio's ProactorPool
+ignores FLAGS_proactor_threads entirely. The fix resets pool_size to 0 when
+--proactor_threads (or DFLY_proactor_threads) is explicitly set, so the flag wins.
+"""
+
+import pytest
+from .instance import DflyInstanceFactory
+
+
+@pytest.mark.asyncio
+async def test_proactor_threads_flag_is_respected(df_factory: DflyInstanceFactory):
+    """Starting with --proactor_threads=N must result in exactly N threads."""
+    server = df_factory.create(proactor_threads=3)
+    server.start()
+    client = server.client()
+    try:
+        info = await client.info("server")
+        assert int(info["thread_count"]) == 3
+    finally:
+        await client.aclose()
+        server.stop()
+
+
+@pytest.mark.asyncio
+async def test_proactor_threads_env_var_is_respected(
+    df_factory: DflyInstanceFactory, monkeypatch
+):
+    """DFLY_proactor_threads env var must behave identically to the CLI flag.
+
+    The subprocess inherits the parent environment, so setting the variable here
+    is equivalent to setting it in a Kubernetes pod's env: section.
+    """
+    monkeypatch.setenv("DFLY_proactor_threads", "2")
+    # No proactor_threads kwarg — only the env var should drive the thread count.
+    server = df_factory.create()
+    server.start()
+    client = server.client()
+    try:
+        info = await client.info("server")
+        assert int(info["thread_count"]) == 2
+    finally:
+        await client.aclose()
+        server.stop()
+
+
+@pytest.mark.asyncio
+async def test_proactor_threads_flag_overrides_env_var(
+    df_factory: DflyInstanceFactory, monkeypatch
+):
+    """CLI flag takes priority over DFLY_proactor_threads env var.
+
+    ParseFlagsFromEnv() skips env vars when the flag was already set on the
+    command line (WasPresentOnCommandLine check), so the CLI value must win.
+    """
+    monkeypatch.setenv("DFLY_proactor_threads", "2")
+    server = df_factory.create(proactor_threads=4)
+    server.start()
+    client = server.client()
+    try:
+        info = await client.info("server")
+        assert int(info["thread_count"]) == 4
+    finally:
+        await client.aclose()
+        server.stop()