From 4381cca95136b0a8222378a41ac0ebb1bc62ea80 Mon Sep 17 00:00:00 2001
From: tomsmeding <tom.smeding@gmail.com>
Date: Sat, 23 Nov 2019 23:36:14 +0100
Subject: Use threads, not processes, to handle requests

---
 main.c   | 74 +++++++++++++++++++++++-----------------------------------------
 plugin.h |  1 +
 util.h   |  3 +++
 3 files changed, 30 insertions(+), 48 deletions(-)

diff --git a/main.c b/main.c
index 0b4886b..debaa3e 100644
--- a/main.c
+++ b/main.c
@@ -1,10 +1,8 @@
-#define _GNU_SOURCE // sigaction
 #include <stdio.h>
 #include <stdbool.h>
 #include <string.h>
-#include <signal.h>
+#include <pthread.h>
 #include <sys/socket.h>
-#include <sys/wait.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <unistd.h>
@@ -19,25 +17,8 @@
 #define PORT 8080
 
 
-int num_threads=0;
-
-
-static void signal_handler(int sig){
-	if(sig==SIGCHLD){
-		int saved_errno=errno;
-		while(true){
-			int status;
-			pid_t pid=waitpid(-1,&status,WNOHANG);
-			if(pid<=0){
-				break;
-			}
-			if(WIFEXITED(status)){
-				num_threads--;
-			}
-		}
-		errno=saved_errno;
-	}
-}
+static int num_threads=0;
+static pthread_mutex_t num_threads_mutex;
 
 
 typedef struct Plugin{
@@ -46,7 +27,8 @@ typedef struct Plugin{
 	struct Plugin *next;
 } Plugin;
 
-Plugin *pluginlist=NULL,*pluginlist_last=NULL;
+// Will only be read once threading starts, so no mutex needed
+static Plugin *pluginlist=NULL,*pluginlist_last=NULL;
 
 static void plugin_register_callback(const char *name,Handler handler){
 	if(pluginlist==NULL){
@@ -82,10 +64,12 @@ static void load_plugin(const char *name){
 }
 
 
-static void connection_handler(int sock){
+static void* thread_entry_connection_handler(void *sock_){
+	int sock=(int)sock_;
+
 	Headers *headers=http_get_headers(sock);
 	if(headers==NULL){
-		return;
+		goto cleanup_exit;
 	}
 
 	for(Plugin *pl=pluginlist;pl!=NULL;pl=pl->next){
@@ -103,6 +87,13 @@ static void connection_handler(int sock){
 		}
 		break;
 	}
+
+cleanup_exit:
+	close(sock);
+	PTHREAD_CHECK(pthread_mutex_lock,&num_threads_mutex);
+	num_threads--;
+	PTHREAD_CHECK(pthread_mutex_unlock,&num_threads_mutex);
+	return NULL;
 }
 
 
@@ -143,17 +134,10 @@ int main(int argc,char **argv){
 		return 1;
 	}
 
-	struct sigaction sa;
-	sa.sa_handler=signal_handler;
-	sigemptyset(&sa.sa_mask);
-	sa.sa_flags=SA_RESTART;
-	if(sigaction(SIGCHLD,&sa,NULL)<0){
-		perror("sigaction");
-		return 1;
-	}
-
 	printf("Listening on port %d\n",PORT);
 
+	PTHREAD_CHECK(pthread_mutex_init,&num_threads_mutex,NULL);
+
 	while(true){
 		struct sockaddr_storage client_addr;
 		socklen_t client_addr_sz=sizeof(client_addr);
@@ -167,20 +151,14 @@ int main(int argc,char **argv){
 		inet_ntop(client_addr.ss_family,&((struct sockaddr_in*)&client_addr)->sin_addr,
 		          str,sizeof(str));
 
-		pid_t pid=fork();
-		if(pid==0){
-			close(sock);
-			connection_handler(clientsock);
-			close(clientsock);
-			exit(0);
-		}
-		if(pid<0){
-			perror("fork");
-			return 1;
-		}
+		printf("Accept from %s; %d thread%s still left\n",str,num_threads,num_threads==1?"":"s");
+
+		PTHREAD_CHECK(pthread_mutex_lock,&num_threads_mutex);
 		num_threads++;
-		printf("Accept from %s; child pid %d, %d thread%s\n",str,pid,num_threads,
-		       num_threads==1?"":"s");
-		close(clientsock);
+		PTHREAD_CHECK(pthread_mutex_unlock,&num_threads_mutex);
+
+		pthread_t th;
+		PTHREAD_CHECK(pthread_create,&th,NULL,thread_entry_connection_handler,(void*)(uintptr_t)clientsock);
+		PTHREAD_CHECK(pthread_detach,th);
 	}
 }
diff --git a/plugin.h b/plugin.h
index d3e8b36..756c45a 100644
--- a/plugin.h
+++ b/plugin.h
@@ -15,4 +15,5 @@ typedef void (*register_callback_t)(const char *name,Handler handler);
 
 // Override this in the plugin; it will be called from the main application.
 // It should call the callback with the plugin's handler.
+// Note that the plugin's handler will be called from multiple threads, so ensure that it is thread-safe.
 void plugin_register_yourself(register_callback_t callback);
diff --git a/util.h b/util.h
index 5457ffe..05cef22 100644
--- a/util.h
+++ b/util.h
@@ -3,6 +3,9 @@
 #include <sys/socket.h>
 
 
+#define PTHREAD_CHECK(func_,...) do { int ret=(func_)(__VA_ARGS__); if(ret!=0){ fprintf(stderr,#func_ ": %s\n",strerror(ret)); exit(1); } } while(0)
+
+
 char* copy_buf(const char *buf,int len);
 char* copy_str(const char *str);
 
-- 
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