mxshadowsrv: Prefork threads

Prefork threads to avoid overhead per client connect.

- Rename MAX_THREADS to THREADS
- Hoist accept loop into client threads
- Do not detach threads, use join instead

mxshadowsrv.c

@@ -62,14 +62,13 @@ static void unmap_shadow(char *shadow_buf, struct stat *statbuf) {
     if (sts == -1) { perror("munmap"); exit(1); }
 }
 
-#define MAX_THREADS 8
+#define THREADS 8
 #define TIMEOUT 30000     // client timeout in msec
 
 static pthread_mutex_t shadow_mutex = PTHREAD_MUTEX_INITIALIZER ;
 static char *shadow_buf = NULL;   // protected by shadow_mutex
 static struct stat statbuf;       // protected by shadow_mutex
 static SSL_CTX *ssl_ctx;
-static sem_t free_worker;
 static int listen_socket;
 static char *filename;
 
@@ -188,12 +187,13 @@ static void process_client(int socket) {
 }
 
 static void *client_thread(void *arg) {
-    int socket = *((int *)arg);
-    process_client(socket);
-    close(socket);
-    free(arg);
-    int status = sem_post(&free_worker);
-    if (status != 0) { errno = status; perror("sem_post"); exit(1); }
+
+    while (1) {
+        int _cleanup_(free_fd) socket = accept4(listen_socket, NULL, NULL, SOCK_NONBLOCK);
+        if (socket == -1 ) { perror("accept"); exit(1); }
+        validate_shadow(&shadow_buf, filename, &statbuf);
+        process_client(socket);
+   }
     return NULL;
 }
 
@@ -260,23 +260,13 @@ int main(int argc, char **argv) {
     status = listen(listen_socket, 40);
     if (status == -1) { perror("listen"); exit(1); }
 
-    status = sem_init(&free_worker, 0, MAX_THREADS);
-    if (status) { errno = status; perror("sem_init"); exit(1); }
-
-    while (1) {
-        int _cleanup_(free_fd) socket = accept4(listen_socket, NULL, NULL, SOCK_NONBLOCK);
-        if (socket == -1 ) { perror("accept"); exit(1); }
-        status = sem_wait(&free_worker);
-        if (status == -1) { perror("sem_wait"); exit(1); }
-        validate_shadow(&shadow_buf, filename, &statbuf);
-        pthread_t thread;
-        int *arg = malloc(sizeof *arg);
-        if (arg == NULL) { perror("malloc"); exit(1); }
-        *arg = socket;
-        status = pthread_create(&thread, NULL, client_thread, arg);
+    pthread_t thread[THREADS];
+    for (int i=0; i<THREADS; i++) {
+        int status = pthread_create(&thread[i], NULL, client_thread, NULL);
         if (status != 0) { errno = status; perror("pthread_create"); exit(1); }
-        socket = -1;
-        status = pthread_detach(thread);
-        if (status != 0) { errno = status; perror("pthread_detach"); exit(1); }
+    }
+    for (int i=0; i<THREADS; i++) {
+        int status = pthread_join(thread[i], NULL);
+        if (status != 0) { errno = status; perror("pthread_join"); exit(1); }
     }
 }