From cf18fb707099d4c2e387dfcd4be859e1cf5d4855 Mon Sep 17 00:00:00 2001
From: Ke Wen <kw2501@meta.com>
Date: Fri, 12 Sep 2025 09:13:49 -0700
Subject: [PATCH] Add GLOO_LOG_LEVEL env

---
 gloo/common/logging.cc | 29 +++++++++++++++++++++++++++++
 gloo/common/logging.h  | 41 +++++++++++++++++++++++++++++++++++++----
 2 files changed, 66 insertions(+), 4 deletions(-)

diff --git a/gloo/common/logging.cc b/gloo/common/logging.cc
index 8d6daed59..d30994b0b 100644
--- a/gloo/common/logging.cc
+++ b/gloo/common/logging.cc
@@ -9,10 +9,39 @@
 #include "gloo/common/logging.h"
 
 #include <algorithm>
+#include <cstring>
 #include <numeric>
 
 namespace gloo {
 
+// Initialize log level from environment variable, and return static value at
+// each inquiry.
+inline LogLevel logLevel() {
+  // Global log level. Initialized once.
+  static LogLevel log_level = LogLevel::UNSET;
+  if (log_level != LogLevel::UNSET) {
+    return log_level;
+  }
+
+  const char* level = getenv("GLOO_LOG_LEVEL");
+  // Defaults to WARN.
+  if (level == nullptr) {
+    log_level = LogLevel::WARN;
+    return log_level;
+  }
+
+  if (std::strcmp(level, "DEBUG") == 0) {
+    log_level = LogLevel::DEBUG;
+  } else if (std::strcmp(level, "INFO") == 0) {
+    log_level = LogLevel::INFO;
+  } else if (std::strcmp(level, "WARN") == 0) {
+    log_level = LogLevel::WARN;
+  } else {
+    log_level = LogLevel::ERROR;
+  }
+  return log_level;
+}
+
 EnforceNotMet::EnforceNotMet(
     const char* file,
     const int line,
diff --git a/gloo/common/logging.h b/gloo/common/logging.h
index a678fdc87..32da6068f 100644
--- a/gloo/common/logging.h
+++ b/gloo/common/logging.h
@@ -20,14 +20,47 @@
 
 namespace gloo {
 
+enum LogLevel {
+  ERROR,
+  WARN,
+  INFO,
+  DEBUG,
+  UNSET,
+};
+
+inline LogLevel logLevel();
+
 #define GLOO_LOG_MSG(level, ...)   \
   std::cerr << ::gloo::MakeString( \
       "[", __FILE__, ":", __LINE__, "] ", level, " ", __VA_ARGS__, "\n")
 
-#define GLOO_INFO(...) GLOO_LOG_MSG("INFO", __VA_ARGS__)
-#define GLOO_ERROR(...) GLOO_LOG_MSG("ERROR", __VA_ARGS__)
-#define GLOO_WARN(...) GLOO_LOG_MSG("WARN", __VA_ARGS__)
-#define GLOO_DEBUG(...) // GLOO_LOG_MSG("DEBUG", __VA_ARGS__)
+#define GLOO_ERROR(...)                   \
+  do {                                    \
+    if (logLevel() >= LogLevel::ERROR) {  \
+      GLOO_LOG_MSG("ERROR", __VA_ARGS__); \
+    }                                     \
+  } while (0)
+
+#define GLOO_WARN(...)                   \
+  do {                                   \
+    if (logLevel() >= LogLevel::WARN) {  \
+      GLOO_LOG_MSG("WARN", __VA_ARGS__); \
+    }                                    \
+  } while (0)
+
+#define GLOO_INFO(...)                   \
+  do {                                   \
+    if (logLevel() >= LogLevel::INFO) {  \
+      GLOO_LOG_MSG("INFO", __VA_ARGS__); \
+    }                                    \
+  } while (0)
+
+#define GLOO_DEBUG(...)                   \
+  do {                                    \
+    if (logLevel() >= LogLevel::DEBUG) {  \
+      GLOO_LOG_MSG("DEBUG", __VA_ARGS__); \
+    }                                     \
+  } while (0)
 
 class EnforceNotMet : public std::exception {
  public: