add macOS ProcessData

docs/macos.md

@@ -0,0 +1,63 @@
+# macOS
+
+Platform-specific code for macOS. Everything in this library, including the headers, is wrapped in the following
+preprocessor macro
+
+```c
+#if defined(__APPLE__) || defined(__MACH__)
+/* 
+... code ...
+*/
+#endif /* defined(__APPLE__) || defined(__MACH__) */
+```
+
+## Structs
+
+### ProcessData
+
+ProcessData is a struct that tracks cpu and memory usage of a process. It needs to be regularly updated with calls to
+`update_process()` in order to provide accurate information
+
+```c
+typedef struct {
+double total_user_time;
+double total_kernel_time;
+double last_total_consumed;
+double percent_cpu;
+
+uint64_t virtual_memory;
+uint64_t resident_memory;
+
+time_t timestamp;
+time_t last_timestamp;
+} ProcessData;
+```
+
+## Functions
+
+## new_ProcessData
+
+Returns a pointer to a `ProcessData` struct.
+
+```c
+ProcessData *new_ProcessData();
+```
+
+## update_process
+
+Updates a `ProcessData` struct. This should be called in a loop or at specific intervals to measure proper usage
+data. An example is below
+
+```c
+int update_process(pid_t pid, ProcessData *proc);
+
+/* Example */
+pid_t pid = getpid();
+ProcessData *pd = new_ProcessData();
+for (int i = 0; i < 10; i++) {
+    update_process(pid, pd);
+    printf("CPU: %.2f\n", pd->percent_cpu);
+    sleep(1);
+}
+free(pd);
+```