Add contrib/membomb/membomb.subthread

When the main thread exits, the whole process becomes invisible
to earlyoom. This is no good.

Relates-to: #309

contrib/membomb/.gitignore

@@ -1 +1,2 @@
 /membomb
+/membomb.subthread

contrib/membomb/Makefile

@@ -1,4 +1,14 @@
 CFLAGS += -Wall -Wextra -g -fstack-protector-all -std=gnu99
 
-membomb: $(wildcard *.c *.h) Makefile
-	$(CC) $(CFLAGS) -o $@ $(wildcard *.c)
+.PHONY: all
+all: membomb membomb.subthread
+
+membomb : $(wildcard *.c *.h) Makefile
+	$(CC) $(CFLAGS) -o $@ eat_all_memory.c membomb.c
+
+membomb.subthread: $(wildcard *.c *.h) Makefile
+	$(CC) $(CFLAGS) -lpthread -o $@ eat_all_memory.c membomb.subthread.c
+
+.PHONY: format
+format:
+	clang-format --style=file -i *.c

contrib/membomb/membomb.c

@@ -3,7 +3,7 @@
 /* Use up all memory that we can get, as fast as we can.
  * As progress information, prints how much memory we already
  * have.
- * 
+ *
  * This file is part of the earlyoom project: https://github.com/rfjakob/earlyoom
  */
 

contrib/membomb/membomb.subthread.c

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: MIT
+
+/* In a subthread, eat up all memory.
+ * The main thread exits and will show up as a zombie.
+ *
+ * This file is part of the earlyoom project: https://github.com/rfjakob/earlyoom
+ */
+
+#define _GNU_SOURCE
+
+#include <pthread.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "eat_all_memory.h"
+
+void* eat_all_memory_thread(__attribute__((__unused__)) void* arg)
+{
+    printf("sub  thread = pid %d\n", gettid());
+    eat_all_memory();
+    return NULL;
+}
+
+int main()
+{
+    printf("main thread = pid %d\n", gettid());
+    pthread_t thread;
+    pthread_create(&thread, NULL, &eat_all_memory_thread, NULL);
+    pthread_exit(NULL);
+}