update control over parallelism

The SWUPD_NUM_THREADS env variable is now understood by all three
commands and overrides the default number of threads. Setting it to 1
is useful while debugging the code that runs inside threads (only one
thread hits breakpoints there). If SWUPD_NUM_THREADS is invalid, a
warning is printed and the variable gets ignored, i.e. the default
parallelism is used.

The hard-coded parallelism of 12 threads when analysing the file system
gets replaced with n, where n is the number of available CPUs. The default
is the same as before elsewhere (n for packing, 3 * n for fullfiles).

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>

include/swupd.h

@@ -257,5 +257,6 @@ extern int system_argv(char *const argv[]);
 extern int system_argv_fd(char *const argv[], int newstdin, int newstdout, int newstderr);
 extern int system_argv_pipe(char *const argvp1[], int stdinp1, int stderrp1,
 			    char *const argvp2[], int stdoutp2, int stderrp2);
+extern int num_threads(float scaling);
 
 #endif

src/analyze_fs.c

@@ -475,6 +475,7 @@ struct manifest *full_manifest_from_directory(int version)
 {
 	struct manifest *manifest;
 	char *dir;
+	int numthreads = num_threads(1.0);
 
 	LOG(NULL, "Computing hashes", "for %i/full", version);
 
@@ -482,7 +483,7 @@ struct manifest *full_manifest_from_directory(int version)
 
 	string_or_die(&dir, "%s/%i/full", image_dir, version);
 
-	threadpool = g_thread_pool_new(get_hash, dir, 12, FALSE, NULL);
+	threadpool = g_thread_pool_new(get_hash, dir, numthreads, FALSE, NULL);
 
 	iterate_directory(manifest, dir, "", true);
 

src/fullfiles.c

@@ -291,10 +291,11 @@ static void submit_fullfile_tasks(GList *files)
 	int ret;
 	int count = 0;
 	GError *err = NULL;
+	int numthreads = num_threads(3.0);
 
-	LOG(NULL, "fullfile threadpool", "%d threads", sysconf(_SC_NPROCESSORS_ONLN) * 3);
+	LOG(NULL, "fullfile threadpool", "%d threads", numthreads);
 	threadpool = g_thread_pool_new(create_fullfile_task, NULL,
-				       sysconf(_SC_NPROCESSORS_ONLN) * 3,
+				       numthreads,
 				       TRUE, NULL);
 
 	printf("Starting downloadable fullfiles data creation\n");

src/helpers.c

@@ -284,3 +284,28 @@ void check_root(void)
 		exit(EXIT_FAILURE);
 	}
 }
+
+int num_threads(float scaling)
+{
+	const char *var = getenv("SWUPD_NUM_THREADS");
+	int result = sysconf(_SC_NPROCESSORS_ONLN) * scaling;
+
+	if (var && *var) {
+		char *endptr;
+		long int value;
+
+		errno = 0;
+		value = strtol(var, &endptr, 0);
+
+		if ((errno != 0 && value == 0) || *endptr) {
+			LOG(NULL, "SWUPD_NUM_THREADS must be an integer", "%s", var);
+		} else if ((errno == ERANGE && (value == LONG_MAX || value == LONG_MIN)) ||
+			   value < 1 || value > INT_MAX) {
+			LOG(NULL, "SWUPD_NUM_THREADS out of range", "%s", var);
+		} else {
+			result = (int)value;
+		}
+	}
+
+	return result;
+}

src/pack.c

@@ -285,10 +285,11 @@ static void make_pack_deltas(GList *files)
 	struct file *file;
 	int ret;
 	GError *err = NULL;
+	int numthreads = num_threads(1.0);
 
-	LOG(NULL, "pack deltas threadpool", "%d threads", sysconf(_SC_NPROCESSORS_ONLN));
+	LOG(NULL, "pack deltas threadpool", "%d threads", numthreads);
 	threadpool = g_thread_pool_new(create_delta, NULL,
-				       sysconf(_SC_NPROCESSORS_ONLN), FALSE, NULL);
+				       numthreads, FALSE, NULL);
 
 	item = g_list_first(files);
 	while (item) {