Added input buffer in stdio_wrap.h to mimic command line behaviour. Added wait on output to avoid race condition with program termination.

jupyter_c_kernel/kernel.py

@@ -72,8 +72,10 @@ class RealTimeSubprocess(subprocess.Popen):
                 if(len(contents) > 0):
                     self._write_to_stdout(contents)
                 readLine = self._read_from_stdin()
+                # need to add newline since it is not captured by frontend
+                readLine += "\n"
+                os.write(1, readLine.encode());
                 self.stdin.write(readLine.encode())
-                self.stdin.write(b"\n")
             else:
                 self._write_to_stdout(contents)
 
@@ -88,7 +90,7 @@ class CKernel(Kernel):
     language = 'c'
     language_version = 'C11'
     language_info = {'name': 'text/x-csrc',
-                     'mimetype': 'text/plain',
+                     'mimetype': 'text/x-csrc',
                      'file_extension': '.c'}
     banner = "C kernel.\n" \
              "Uses gcc, compiles in C11, and creates source code files and executables in temporary folder.\n"
@@ -188,10 +190,10 @@ class CKernel(Kernel):
     # also add common magics like -lm
     def _add_main(self, magics, code):
         # remove comments
-        tmpCode = re.sub("//.*", "", code)
-        tmpCode = re.sub("/\*.*?\*/", "", tmpCode, flags=re.M|re.S)
+        tmpCode = re.sub(r"//.*", "", code)
+        tmpCode = re.sub(r"/\*.*?\*/", "", tmpCode, flags=re.M|re.S)
 
-        x = re.search("int\s+main\s*\(", tmpCode)
+        x = re.search(r"int\s+main\s*\(", tmpCode)
 
         if not x:
             code = self.main_head + code + self.main_foot
@@ -234,6 +236,11 @@ class CKernel(Kernel):
         p = self.create_jupyter_subprocess([self.master_path, binary_file.name] + magics['args'])
         while p.poll() is None:
             p.write_contents()
+
+        # wait for threads to finish, so output is always shown
+        p._stdout_thread.join()
+        p._stderr_thread.join()
+
         p.write_contents()
 
         # now remove the files we have just created

jupyter_c_kernel/resources/stdio_wrap.h

@@ -3,22 +3,76 @@
 
 #include <stdio.h>
 #include <stdarg.h>
+#include <string.h>
+
+/* Need input buffer to know whether we need another input request */
+char inputBuff[1<<10] = "";
+
+/* read remaining input into buffer so it can be used in next call */
+void readIntoBuffer() {
+  long length = strlen(inputBuff);
+  char nextChar = 0;
+    while((nextChar = getchar()) != '\n'){
+      inputBuff[length++] = nextChar;
+    }
+    inputBuff[length++] = '\n';
+    inputBuff[length] = '\0';
+}
 
 /* Define the functions to overload the old ones */
 int scanf_wrap(const char *format, ...) {
-  printf("<inputRequest>");
-  fflush(stdout);
+  /* unget chars in buffer */
+  int doRequest = 1;
+  long index = strlen(inputBuff) - 1;
+  // printf("Start index: %ld\n", index);
+  for(; index >= 0; --index) {
+    ungetc(inputBuff[index], stdin);
+    /* if there already is a newline in buffer
+      we need no input request */
+    if(inputBuff[index] == '\n') {
+      doRequest = 0;
+    }
+  }
+  /* Buffer will always be empty after scanf call
+    since there is no way to enter more than one
+    newline in the frontend */
+  inputBuff[0] = '\0';
+  // printf("doRequest: %d\n", doRequest);
+  if(doRequest) {
+    printf("<inputRequest>");
+    fflush(stdout);
+  }
   va_list arglist;
   va_start( arglist, format );
   int result = vscanf( format, arglist );
   va_end( arglist );
+
   return result;
 }
 
 int getchar_wrap(){
-  printf("<inputRequest>");
-  fflush(stdout);
-  return getchar();
+  /* check if there is still something in the input buffer*/
+  char input = 0;
+  long length = strlen(inputBuff);
+  if(length <= 0) {
+    printf("<inputRequest>");
+    fflush(stdout);
+
+    input = getchar();
+    readIntoBuffer();
+  } else {
+    input = inputBuff[0];
+    /* shift all chars one to the left */
+    int i = 1;
+    for(; i < 100; ++i){
+      inputBuff[i-1] = inputBuff[i];
+      if(inputBuff[i] == '\0') {
+        break;
+      }
+    }
+  }
+
+  return input;
 }
 
 /* Replace all the necessary input functions