Use File Locking

launcher/src/bootstrap.c

@@ -193,10 +193,24 @@ void run_simple_command(const char *const command[], const char *error) {
         ERR("%s", error);
     }
 }
+#define HOME_SUBDIRECTORY_FOR_SDK HOME_SUBDIRECTORY_FOR_GAME_DATA "/sdk"
 static void copy_sdk(char *binary_directory) {
+    // Ensure SDK Directory
+    {
+        char *sdk_path = NULL;
+        safe_asprintf(&sdk_path, "%s" HOME_SUBDIRECTORY_FOR_SDK, getenv("HOME"));
+        const char *const command[] = {"mkdir", "-p", sdk_path, NULL};
+        run_simple_command(command, "Unable To Create SDK Directory");
+    }
+
+    // Lock File
+    char *lock_file_path = NULL;
+    safe_asprintf(&lock_file_path, "%s" HOME_SUBDIRECTORY_FOR_SDK "/.lock", getenv("HOME"));
+    int lock_file_fd = lock_file(lock_file_path);
+
     // Output Directory
     char *output = NULL;
-    safe_asprintf(&output, "%s" HOME_SUBDIRECTORY_FOR_GAME_DATA "/sdk/" MCPI_SDK_DIR, getenv("HOME"));
+    safe_asprintf(&output, "%s" HOME_SUBDIRECTORY_FOR_SDK "/" MCPI_SDK_DIR, getenv("HOME"));
     // Source Directory
     char *source = NULL;
     safe_asprintf(&source, "%s/sdk/.", binary_directory);
@@ -222,6 +236,10 @@ static void copy_sdk(char *binary_directory) {
     // Free
     free(output);
     free(source);
+
+    // Unlock File
+    unlock_file(lock_file_path, lock_file_fd);
+    free(lock_file_path);
 }
 
 // Bootstrap

launcher/src/client/cache.cpp

@@ -30,30 +30,34 @@ launcher_cache load_cache() {
     // Log
     DEBUG("Loading Launcher Cache...");
 
+    // Lock File
+    int lock_fd = lock_file(get_cache_path().c_str());
+
+    // Return Value
+    launcher_cache ret = empty_cache;
+
     // Open File
     std::ifstream stream(get_cache_path(), std::ios::in | std::ios::binary);
     if (!stream) {
-        // No Warning If File Doesn't Exist
+        // Fail
         struct stat s;
+        // No Warning If File Doesn't Exist
         if (stat(get_cache_path().c_str(), &s) == 0) {
             WARN("Unable To Open Launcher Cache For Loading");
         }
-        return empty_cache;
-    }
-
+    } else {
         // Check Version
         unsigned char cache_version;
         stream.read((char *) &cache_version, 1);
         if (stream.eof() || cache_version != (unsigned char) CACHE_VERSION) {
+            // Fail
             if (!stream.eof()) {
                 WARN("Invalid Launcher Cache Version (Expected: %i, Actual: %i)", (int) CACHE_VERSION, (int) cache_version);
             } else {
                 WARN("Unable To Read Launcher Cache Version");
             }
             stream.close();
-        return empty_cache;
-    }
-
+        } else {
             // Load Username And Render Distance
             launcher_cache cache;
             std::getline(stream, cache.username, '\0');
@@ -73,12 +77,20 @@ launcher_cache load_cache() {
             // Finish
             stream.close();
             if (!stream) {
+                // Fail
                 WARN("Failure While Loading Launcher Cache");
-        return empty_cache;
+            } else {
+                // Success
+                ret = cache;
+            }
+        }
     }
 
+    // Unlock File
+    unlock_file(get_cache_path().c_str(), lock_fd);
+
     // Return
-    return cache;
+    return ret;
 }
 
 // Save
@@ -94,13 +106,15 @@ void save_cache() {
     // Log
     DEBUG("Saving Launcher Cache...");
 
+    // Lock File
+    int lock_fd = lock_file(get_cache_path().c_str());
+
     // Open File
     std::ofstream stream(get_cache_path(), std::ios::out | std::ios::binary);
     if (!stream) {
+        // Fail
         WARN("Unable To Open Launcher Cache For Saving");
-        return;
-    }
-
+    } else {
         // Save Cache Version
         unsigned char cache_version = (unsigned char) CACHE_VERSION;
         stream.write((const char *) &cache_version, 1);
@@ -139,6 +153,10 @@ void save_cache() {
         if (!stream.good()) {
             WARN("Failure While Saving Launcher Cache");
         }
+    }
+
+    // Unlock File
+    unlock_file(get_cache_path().c_str(), lock_fd);
 }
 
 // Wipe Cache

libreborn/include/libreborn/util.h

@@ -41,6 +41,10 @@ void safe_pipe2(int pipefd[2], int flags);
 // Check If Two Percentages Are Different Enough To Be Logged
 int is_progress_difference_significant(int32_t new_val, int32_t old_val);
 
+// Lock File
+int lock_file(const char *file);
+void unlock_file(const char *file, int fd);
+
 #ifdef __cplusplus
 }
 #endif

libreborn/src/util/util.c

@@ -1,3 +1,6 @@
+#include <fcntl.h>
+#include <sys/file.h>
+
 #include <libreborn/util.h>
 
 // Safe Version Of pipe()
@@ -22,3 +25,21 @@ int is_progress_difference_significant(int32_t new_val, int32_t old_val) {
         return 0;
     }
 }
+
+// Lock File
+int lock_file(const char *file) {
+    int fd = open(file, O_WRONLY | O_CREAT, S_IWUSR);
+    if (fd == -1) {
+        ERR("Unable To Open Lock File: %s: %s", file, strerror(errno));
+    }
+    if (flock(fd, LOCK_EX) == -1) {
+        ERR("Unable To Lock File: %s: %s", file, strerror(errno));
+    }
+    return fd;
+}
+void unlock_file(const char *file, int fd) {
+    if (flock(fd, LOCK_UN) == -1) {
+        ERR("Unable To Unlock File: %s: %s", file, strerror(errno));
+    }
+    close(fd);
+}