From 34c53bc3d396934df94431f7b76972180b1b0a8c Mon Sep 17 00:00:00 2001
From: Trumeet <yuuta@yuuta.moe>
Date: Sat, 23 Jul 2022 11:32:53 -0700
Subject: feat(acronc): guard the connection using a mutex

Signed-off-by: Trumeet <yuuta@yuuta.moe>
---
 client/libacron/README.md     |  3 ++
 client/libacron/acronc/main.c | 85 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 88 insertions(+)

diff --git a/client/libacron/README.md b/client/libacron/README.md
index 09e36dc..d52a4c3 100644
--- a/client/libacron/README.md
+++ b/client/libacron/README.md
@@ -261,6 +261,9 @@ it is the caller's responsibility to guard the whole connection with a mutex. li
 provide that because this may limit the flexibility. After locking, it is safe to call the
 connection-related functions from any threads.
 
+Example `acronc/main.c` has a naive cross-platform example of how to guard the connection using
+a mutex.
+
 ## Roadmap
 
 * Make unit tests
diff --git a/client/libacron/acronc/main.c b/client/libacron/acronc/main.c
index 43802ad..dfd1668 100644
--- a/client/libacron/acronc/main.c
+++ b/client/libacron/acronc/main.c
@@ -15,6 +15,65 @@
 
 #endif
 
+#ifdef __STDC_NO_THREADS__
+# ifdef WIN32
+#define THREAD_WIN32
+#include <windows.h>
+static HANDLE mtx_conn;
+
+int lock(void) { \
+DWORD _dwlck = WaitForSingleObject(mtx_conn, 0); \
+if (_dwlck == WAIT_FAILED) { _dwlck = GetLastError(); } \
+if (_dwlck) { fprintf(stderr, "Cannot lock the mutex: %d.\n", _dwlck); return _dwlck; } \
+return 0; \
+}
+
+int unlock(void) { \
+if (!ReleaseMutex(mtx_conn)) { \
+int r = GetLastError();        \
+fprintf(stderr, "Cannot release the mutex: %d.\n", r); \
+return r;      \
+} \
+return 0;    \
+}
+
+# else
+#error "Either C11 threading or Win32 API is required for concurrency."
+# endif
+#else
+
+#define THREAD_C11
+
+#include <threads.h>
+
+static mtx_t mtx_conn;
+
+int lock(void) {
+    \
+if (mtx_lock(&mtx_conn) != thrd_success) {
+        \
+fprintf(stderr, "Cannot lock the mutex.\n"); \
+return 1;    \
+
+    }            \
+return 0;   \
+
+}
+
+int unlock(void) {
+    \
+if (mtx_unlock(&mtx_conn) != thrd_success) {
+        \
+fprintf(stderr, "Cannot release the mutex.\n"); \
+return 1;      \
+
+    }              \
+return 0; \
+
+}
+
+#endif
+
 static const char *world_name(const enum ac_world world) {
     switch (world) {
         case overworld:
@@ -168,6 +227,19 @@ int main(int argc, char **argv) {
     if ((r = net_init())) {
         return r;
     }
+#if defined(THREAD_WIN32)
+    if (!(mtx_conn = CreateMutex(NULL, TRUE, NULL))) {
+        r = GetLastError();
+        fprintf(stderr, "Cannot create mutex: %d.\n", r);
+        return r;
+    }
+#elif defined(THREAD_C11)
+    if (mtx_init(&mtx_conn, mtx_plain) != thrd_success) {
+        fprintf(stderr, "Cannot create mutex.\n");
+        return 1;
+    }
+#endif
+
 #ifdef WIN32
     fprintf(stderr, "Warning: ^C handler on Windows is not yet available.\n");
 #else
@@ -235,12 +307,15 @@ int main(int argc, char **argv) {
                 goto end;
             }
         }
+        if ((r = lock())) { goto end; }
         if ((r = ac_receive(connection, buffer, bytes, &obj))) {
+            if ((r = unlock())) { goto end; }
             goto end;
         }
         if (!ready) {
             /* Wait until ready. */
             if ((r = ac_get_state(connection, &state))) {
+                if ((r = unlock())) { goto end; }
                 goto end;
             }
             switch (state) {
@@ -250,12 +325,15 @@ int main(int argc, char **argv) {
                     printf("Connection is established.\n");
                     ready = true;
                     say(connection);
+                    if ((r = unlock())) { goto end; }
                     continue;
                 default:
                     fprintf(stderr, "Unexpected state.\n");
+                    if ((r = unlock())) { goto end; }
                     goto end;
             }
         }
+        if ((r = unlock())) { goto end; }
 
         if (!obj) {
             continue;
@@ -277,9 +355,16 @@ int main(int argc, char **argv) {
                     nr);
         }
     }
+    if ((r = lock())) { goto end; }
     ac_disconnect(connection);
+    if ((r = unlock())) { goto end; }
     net_close(&sock);
     ac_free();
     net_free();
+#if defined(THREAD_WIN32)
+    CloseHandle(mtx_conn);
+#elif defined(THREAD_C11)
+    mtx_destroy(&mtx_conn);
+#endif
     return r;
 }
\ No newline at end of file
-- 
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