CORE: Add UCC_DEBUGGER_WAIT env

Author: nsarka

src/core/ucc_context.c

@@ -12,6 +12,7 @@
 #include "utils/ucc_log.h"
 #include "utils/ucc_list.h"
 #include "utils/ucc_string.h"
+#include "utils/ucc_debug.h"
 #include "ucc_progress_queue.h"
 
 static uint32_t ucc_context_seq_num = 0;
@@ -633,6 +634,9 @@ ucc_status_t ucc_context_create_proc_info(ucc_lib_h                   lib,
     b_params.thread_mode       = lib->attr.thread_mode;
     if (params->mask & UCC_CONTEXT_PARAM_FIELD_OOB) {
         ctx->rank = params->oob.oob_ep;
+#ifdef ENABLE_DEBUG
+        ucc_check_wait_for_debugger(ctx->rank);
+#endif
     }
     status = ucc_create_tl_contexts(ctx, config, b_params);
     if (UCC_OK != status) {

src/utils/ucc_debug.h

@@ -0,0 +1,32 @@
+/**
+ * Copyright (c) 2020-2025, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ *
+ * See file LICENSE for terms.
+ */
+
+#ifndef UCC_DEBUG_H_
+#define UCC_DEBUG_H_
+
+#include "config.h"
+#include "ucc/api/ucc.h"
+
+static inline void ucc_check_wait_for_debugger(ucc_rank_t ctx_rank)
+{
+    const char *wait_for_rank;
+    if (NULL != (wait_for_rank = getenv("UCC_DEBUGGER_WAIT"))) {
+	volatile int waiting = 1;
+	if (atoi(wait_for_rank) == ctx_rank) {
+	    char hostname[256];
+	    gethostname(hostname, sizeof(hostname));
+	    printf("PID %d (ctx rank %d) waiting for attach on %s\n"
+		   "Set var waiting = 0 in debugger to continue\n",
+		   getpid(), ctx_rank, hostname);
+	    while (waiting) {
+		sleep(1);
+	    }
+	}
+    }
+}
+
+#endif
+