apk: add --wait option to wait for exclusive lock (fixes #26)

src/apk.c

@@ -24,23 +24,27 @@
 
 const char *apk_root;
 struct apk_repository_url apk_repository_list;
-int apk_verbosity = 1, apk_cwd_fd;
+int apk_verbosity = 1, apk_cwd_fd, apk_wait;
 unsigned int apk_flags = 0;
 
 static struct apk_option generic_options[] = {
 	{ 'h', "help",		"Show generic help or applet specific help" },
 	{ 'p', "root",		"Install packages to DIR",
-	  required_argument, "DIR" },
+				required_argument, "DIR" },
 	{ 'X', "repository",	"Use packages from REPO",
-	  required_argument, "REPO" },
+				required_argument, "REPO" },
 	{ 'q', "quiet",		"Print less information" },
 	{ 'v', "verbose",	"Print more information" },
 	{ 'V', "version",	"Print program version and exit" },
 	{ 'f', "force",		"Do what was asked even if it looks dangerous" },
 	{ 0x101, "progress",	"Show a progress bar" },
-	{ 0x102, "clean-protected",
-		 "Do not create .apk-new files to configuration dirs" },
-	{ 0x104, "simulate",	"Show what would be done without actually doing it" },
+	{ 0x102, "clean-protected", "Do not create .apk-new files to "
+				"configuration dirs" },
+	{ 0x104, "simulate",	"Show what would be done without actually "
+				"doing it" },
+	{ 0x105, "wait",	"Wait for TIME seconds to get an exclusive "
+				"repository lock before failing",
+				required_argument, "TIME" },
 };
 
 void apk_log(const char *prefix, const char *format, ...)
@@ -305,6 +309,9 @@ int main(int argc, char **argv)
 		case 0x104:
 			apk_flags |= APK_SIMULATE;
 			break;
+		case 0x105:
+			apk_wait = atoi(optarg);
+			break;
 		default:
 			if (applet == NULL || applet->parse == NULL ||
 			    applet->parse(ctx, r,

src/apk_defines.h

@@ -50,7 +50,7 @@ extern csum_t bad_checksum;
 #define csum_valid(buf)			memcmp(buf, bad_checksum, sizeof(csum_t))
 #endif
 
-extern int apk_cwd_fd, apk_verbosity;
+extern int apk_cwd_fd, apk_verbosity, apk_wait;
 extern unsigned int apk_flags;
 
 #define APK_FORCE		0x0001

src/database.c

@@ -17,6 +17,7 @@
 #include <malloc.h>
 #include <string.h>
 #include <stdlib.h>
+#include <signal.h>
 #include <sys/file.h>
 
 #include "apk_defines.h"
@@ -653,6 +654,10 @@ static int apk_db_create(struct apk_database *db)
 	return 0;
 }
 
+static void handle_alarm(int sig)
+{
+}
+
 int apk_db_open(struct apk_database *db, const char *root, unsigned int flags)
 {
 	const char *apk_repos = getenv("APK_REPOS"), *msg = NULL;
@@ -698,8 +703,24 @@ int apk_db_open(struct apk_database *db, const char *root, unsigned int flags)
 			}
 			if (db->lock_fd < 0 ||
 			    flock(db->lock_fd, LOCK_EX | LOCK_NB) < 0) {
-				msg = "Unable to lock database";
-				goto ret_errno;
+				if (apk_wait) {
+					struct sigaction sa, old_sa;
+
+					apk_message("Waiting for repository lock");
+					memset(&sa, 0, sizeof sa);
+					sa.sa_handler = handle_alarm;
+					sa.sa_flags   = SA_ONESHOT;
+					sigaction(SIGALRM, &sa, &old_sa);
+
+					alarm(apk_wait);
+					if (flock(db->lock_fd, LOCK_EX) < 0) {
+						msg = "Unable to lock database";
+						goto ret_errno;
+					}
+
+					alarm(0);
+					sigaction(SIGALRM, &old_sa, NULL);
+				}
 			}
 		}
 	}