Use a spinlock on the log writer.

server.c

@@ -77,6 +77,7 @@ server_new(const char *cfg_file) {
 	struct server *s = calloc(1, sizeof(struct server));
 
 	s->cfg = conf_read(cfg_file);
+	pthread_spin_init(&s->log_lock, PTHREAD_PROCESS_SHARED);
 
 	/* workers */
 	s->w = calloc(s->cfg->http_threads, sizeof(struct worker*));

server.h

@@ -3,6 +3,7 @@
 
 #include <event.h>
 #include <hiredis/async.h>
+#include <pthread.h>
 
 struct worker;
 struct conf;
@@ -18,6 +19,9 @@ struct server {
 	/* worker threads */
 	struct worker **w;
 	int next_worker;
+
+	/* log lock */
+	pthread_spinlock_t log_lock;
 };
 
 struct server *

slog.c

@@ -5,12 +5,14 @@
 #include <time.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <pthread.h>
 
 #include "slog.h"
 #include "server.h"
 #include "conf.h"
 
-void slog(const struct server *s, log_level level,
+void
+slog(struct server *s, log_level level,
 		const char *body, size_t sz) {
 
 	const char *c = ".-*#";
@@ -19,13 +21,16 @@ void slog(const struct server *s, log_level level,
 	char buf[64];
 	char msg[124];
 
+
 	static pid_t self = 0;
 	if(!self) self = getpid();
 
 	if(level > s->cfg->verbosity) return; /* too verbose */
 
+	pthread_spin_lock(&s->log_lock);
+
 	if(!fp) fp = (s->cfg->logfile == NULL) ? stdout : fopen(s->cfg->logfile, "a");
-	if(!fp) return;
+	if(!fp) goto end;
 
 	/* limit message size */
 	snprintf(msg, sz + 1 > sizeof(msg) ? sizeof(msg) : sz + 1, "%s", body);
@@ -33,4 +38,7 @@ void slog(const struct server *s, log_level level,
 	strftime(buf,sizeof(buf),"%d %b %H:%M:%S",localtime(&now));
 	fprintf(fp,"[%d] %s %c %s\n", (int)self, buf, c[level], msg);
 	fflush(fp);
+
+end:
+	pthread_spin_unlock(&s->log_lock);
 }

slog.h

@@ -11,7 +11,7 @@ typedef enum {
 
 struct server;
 
-void slog(const struct server *s, log_level level,
+void slog(struct server *s, log_level level,
 		const char *body, size_t sz);
 
 #endif

worker.c

@@ -204,10 +204,12 @@ worker_process_client(struct http_client *c) {
 	switch(ret) {
 		case CMD_ACL_FAIL:
 		case CMD_PARAM_ERROR:
+			slog(w->s, WEBDIS_DEBUG, "403", 3);
 			http_send_error(c, 403, "Forbidden");
 			break;
 
 		case CMD_REDIS_UNAVAIL:
+			slog(w->s, WEBDIS_DEBUG, "503", 3);
 			http_send_error(c, 503, "Service Unavailable");
 			break;
 		default: