Daemonize async process to automatically reap the child when it dies

2 files changed, 32 insertions, 13 deletions

diff --git a/include/Program.h b/include/Program.h
index bc3e91e..cd45b30 100644
--- a/include/Program.h
+++ b/include/Program.h
@@ -30,7 +30,9 @@ bool wait_program_non_blocking(pid_t process_id, int *status);
 
 /*
     @args need to have at least 2 arguments. The first which is the program name
-    and the last which is NULL, which indicates end of args
+    and the last which is NULL, which indicates end of args.
+    @result_process_id should be set to NULL if you are not interested in the exit status of the child process
+    and you want the child process to be cleaned up automatically when it dies.
 */
 int exec_program_async(const char **args, pid_t *result_process_id);
 #if 0
diff --git a/src/Program.c b/src/Program.c
index fe2ae3f..bb476c4 100644
--- a/src/Program.c
+++ b/src/Program.c
@@ -33,12 +33,12 @@ int exec_program(const char **args, ProgramOutputCallback output_callback, void
     } else if(pid == 0) { /* child */
         if(prctl(PR_SET_PDEATHSIG, SIGTERM) == -1) {
             perror("prctl(PR_SET_PDEATHSIG, SIGTERM) failed");
-            exit(127);
+            _exit(127);
         }
 
         /* Test if the parent died before the above call to prctl */
         if(getppid() != parent_pid)
-            exit(127);
+            _exit(127);
 
         dup2(fd[WRITE_END], STDOUT_FILENO);
         close(fd[READ_END]);
@@ -46,7 +46,7 @@ int exec_program(const char **args, ProgramOutputCallback output_callback, void
 
         execvp(args[0], args);
         perror("execvp");
-        exit(127);
+        _exit(127);
     } else { /* parent */
         close(fd[WRITE_END]);
 
@@ -151,16 +151,33 @@ int exec_program_async(const char **args, pid_t *result_process_id) {
         perror("Failed to fork");
         return -err;
     } else if(pid == 0) { /* child */
-        if(prctl(PR_SET_PDEATHSIG, SIGTERM) == -1) {
-            perror("prctl(PR_SET_PDEATHSIG, SIGTERM) failed");
-            exit(127);
-        }
-
-        /* Test if the parent died before the above call to prctl */
-        if(getppid() != parent_pid)
-            exit(127);
+        if(result_process_id) {
+            if(prctl(PR_SET_PDEATHSIG, SIGTERM) == -1) {
+                perror("prctl(PR_SET_PDEATHSIG, SIGTERM) failed");
+                _exit(127);
+            }
 
-        execvp(args[0], args);
+            /* Test if the parent died before the above call to prctl */
+            if(getppid() != parent_pid)
+                _exit(127);
+
+            execvp(args[0], args);
+            perror("execvp");
+            _exit(127);
+        } else {
+            setsid();
+            signal(SIGHUP, SIG_IGN);
+
+            // Daemonize child to make the parent the init process which will reap the zombie child
+            pid_t second_child = fork();
+            if(second_child == 0) { // child
+                execvp(args[0], args);
+                perror("execvp");
+                _exit(127);
+            } else if(second_child != -1) {
+                _exit(0);
+            }
+        }
     } else { /* parent */
         if(result_process_id)
             *result_process_id = pid;