Add supervisor

include/ucore/supervisor.h

@@ -0,0 +1,22 @@
+#ifndef UCORE_SUPERVISOR_H_
+#define UCORE_SUPERVISOR_H_
+
+/** Supervises this process - restart if it dies.
+ *
+ *  The program should call supervise() at a pristine state (all relevant file descriptors closed, etc).
+ *  supervise() will return 0 if all is ok, and the program can continue.(returning != 0 means 
+ *  the supervisor couldn't start, and the calling process must exit)
+ *
+ *  This will run the actual process as a child process. If that child process dies by any means,
+ *  supervise will create another child process, where supervise() returns 0 again.
+ *
+ * To kill the supervisor process and the supervised process, send SIGERM/SIGHUP/SIGINT to the 
+ * parent supervisor process.
+ * Sending SIGUSR1 to the parent supervisor process will terminate the current child process and
+ * restart it.
+ *
+ * The supervised child process must exit if it recieves a SIGTERM 
+ * @return 0 on success, non-zero on failure (e.g. fork() fails)*/
+int uc_supervise(void);
+
+#endif

src/supervisor.c

@@ -0,0 +1,194 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <syslog.h>
+#include <errno.h>
+#include <string.h>
+#include <limits.h>
+
+
+#define CLEAN_EXIT 11
+#define BAD_EXIT   22
+#define RESTART    33
+
+//seconds to wait before restarting the process
+#define RESTART_GRACE 1
+
+static volatile sig_atomic_t restart_flag = 0;
+static volatile sig_atomic_t exit_flag = 0;
+
+static void restart_handler(int sig)
+{
+    (void)sig;
+    restart_flag = 1;
+}
+
+static void exit_handler(int sig)
+{
+    (void)sig;
+    exit_flag = 1;
+}
+
+static void kill_supervised_process(pid_t pid)
+{
+    kill(pid, SIGTERM);
+    /* Todo.. verify we killed it, otherwise take more 
+     * desperate measures*/
+}
+
+static int watch(pid_t pid)
+{
+    int status;
+    pid_t rc;
+
+restart:
+    rc = waitpid(pid, &status, 0);
+    if (rc == -1 && errno == EINTR) {
+        if (restart_flag) {
+            restart_flag = 0;
+            kill_supervised_process(pid);
+            /* next waitpid should notify us of the death and
+             * we'll restart the process */
+            goto restart;
+        } else if (exit_flag) {
+            exit_flag = 0;
+            return CLEAN_EXIT;
+        }
+
+        goto restart;
+
+    } else if (rc == -1) {
+        return BAD_EXIT;
+    }
+    
+    if (WIFSIGNALED(status)) {
+        syslog(LOG_ERR, "supervised process(pid %ld) exited cause of signal %d, status = 0x%X", (long)pid, WTERMSIG(status), status);
+        return RESTART;
+    } else if (WIFEXITED(status)) {
+        syslog(LOG_ERR, "supervised process(pid %ld) exited with code %d, status = 0x%X", (long)pid, WTERMSIG(status), status);
+        return RESTART;
+    }
+
+    /* Ok, can we ever get here ? */
+
+    syslog(LOG_ERR, "waitpid of supervised process(pid %ld) status = 0x%X", (long)pid, status);
+    if (kill(pid, 0) == 0) {
+        syslog(LOG_ERR, "supervised process(pid %ld) seems to still be alive, not restarting", (long)pid);
+        goto restart;
+    } 
+    
+    return RESTART;
+}
+
+static struct sigaction orig_usr1_sa;
+static struct sigaction orig_term_sa;
+static struct sigaction orig_hup_sa;
+static struct sigaction orig_int_sa;
+
+static void restore_signal_handlers(void)
+{
+    sigaction(SIGUSR1, &orig_usr1_sa, NULL);
+    sigaction(SIGTERM, &orig_term_sa, NULL);
+    sigaction(SIGHUP,  &orig_hup_sa,  NULL);
+    sigaction(SIGINT,  &orig_int_sa,  NULL);
+}
+
+static void install_signal_handlers(void)
+{
+    struct sigaction act;
+    memset(&act, 0, sizeof act);
+
+    act.sa_handler = restart_handler;
+    sigaction(SIGUSR1, &act, &orig_usr1_sa);
+
+    act.sa_handler = exit_handler;
+    sigaction(SIGTERM, &act, &orig_term_sa);
+    sigaction(SIGHUP,  &act, &orig_hup_sa);
+    sigaction(SIGINT,  &act, &orig_int_sa);
+}
+
+/** Supervises this process - restart if it dies.
+ *
+ *  The program should call supervise() at a pristine state (all relevant file descriptors closed, etc).
+ *  supervise() will return 0 if all is ok, and the program can continue.(returning != 0 means 
+ *  the supervisor couldn't start, and the calling process must exit)
+ *
+ *  This will run the actual process as a child process. If that child process dies by any means,
+ *  supervise will create another child process, where supervise() returns 0 again.
+ *
+ * To kill the supervisor process and the supervised process, send SIGERM/SIGHUP/SIGINT to the 
+ * parent supervisor process.
+ * Sending SIGUSR1 to the parent supervisor process will terminate the current child process and
+ * restart it.
+ *
+ * The supervised child process must exit if it recieves a SIGTERM */
+int uc_supervise(void)
+{
+   pid_t pid;
+
+    pid = fork();
+    if (pid == -1) {
+        syslog(LOG_ERR, "Cannot create supervisor : %s", strerror(errno));
+        return -1;
+    } else if (pid == 0) {
+        return 0;
+    }
+
+    //close_files();
+    install_signal_handlers();
+
+    syslog(LOG_INFO, "Supervising pid %ld", (long)pid);     
+
+    for (;;) {
+        int cmd = watch(pid);
+        switch (cmd) {
+
+            case CLEAN_EXIT:
+                syslog(LOG_INFO, "Terminating supervised pid %lu", (unsigned long)pid);     
+                kill_supervised_process(pid);
+                wait(NULL);
+                syslog(LOG_INFO, "Exiting");
+                exit(0);
+                break;
+
+            case BAD_EXIT:
+                syslog(LOG_ERR, "watch() error, exiting");
+                exit(55);
+                break;
+
+            case RESTART: {
+                pid_t new_pid = -1;
+
+                while (new_pid == -1) {
+                    sleep(RESTART_GRACE);
+                    syslog(LOG_INFO, "Restarting supervised pid %lu", (unsigned long)pid);     
+                    closelog();
+                    new_pid = fork();
+                    if (new_pid == -1) {
+                        syslog(LOG_INFO, "Cannot restart. %s", strerror(errno));
+                    } else if (new_pid == 0) { //return so the original process continues 
+                        restore_signal_handlers();
+                        return 0;
+                    }
+                }
+
+                pid = new_pid;
+                syslog(LOG_INFO, "Supervising new pid %lu", (unsigned long)new_pid);     
+                }
+
+                break;
+
+            default:
+                exit(38);
+                break;
+        }
+                
+    }
+
+    return 0x76;
+}
+
+