LibC: Implement fgetc_unlocked(), fread_unlocked() and getc_unlocked()

Author: https://github.com/gunnarbeutner
Commit: https://github.com/SerenityOS/serenity/commit/6adb0dbdba0
Pull-request: https://github.com/SerenityOS/serenity/pull/6744

Userland/Libraries/LibC/stdio.cpp

@@ -666,6 +666,16 @@ int fgetc(FILE* stream)
     return EOF;
 }
 
+int fgetc_unlocked(FILE* stream)
+{
+    VERIFY(stream);
+    char ch;
+    size_t nread = fread_unlocked(&ch, sizeof(char), 1, stream);
+    if (nread == 1)
+        return ch;
+    return EOF;
+}
+
 int getc(FILE* stream)
 {
     return fgetc(stream);
@@ -673,8 +683,7 @@ int getc(FILE* stream)
 
 int getc_unlocked(FILE* stream)
 {
-    // FIXME: This currently locks the file
+    return fgetc_unlocked(stream);
-    return fgetc(stream);
 }
 
 int getchar()
@@ -796,18 +805,24 @@ int ferror(FILE* stream)
     return stream->error();
 }
 
-size_t fread(void* ptr, size_t size, size_t nmemb, FILE* stream)
+size_t fread_unlocked(void* ptr, size_t size, size_t nmemb, FILE* stream)
 {
     VERIFY(stream);
     VERIFY(!Checked<size_t>::multiplication_would_overflow(size, nmemb));
 
-    ScopedFileLock lock(stream);
     size_t nread = stream->read(reinterpret_cast<u8*>(ptr), size * nmemb);
     if (!nread)
         return 0;
     return nread / size;
 }
 
+size_t fread(void* ptr, size_t size, size_t nmemb, FILE* stream)
+{
+    VERIFY(stream);
+    ScopedFileLock lock(stream);
+    return fread_unlocked(ptr, size, nmemb, stream);
+}
+
 size_t fwrite(const void* ptr, size_t size, size_t nmemb, FILE* stream)
 {
     VERIFY(stream);

Userland/Libraries/LibC/stdio.h

@@ -47,6 +47,7 @@ char* fgets(char* buffer, int size, FILE*);
 int fputc(int ch, FILE*);
 int fileno(FILE*);
 int fgetc(FILE*);
+int fgetc_unlocked(FILE*);
 int getc(FILE*);
 int getc_unlocked(FILE* stream);
 int getchar();
@@ -66,6 +67,7 @@ int ferror(FILE*);
 int feof(FILE*);
 int fflush(FILE*);
 size_t fread(void* ptr, size_t size, size_t nmemb, FILE*);
+size_t fread_unlocked(void* ptr, size_t size, size_t nmemb, FILE*);
 size_t fwrite(const void* ptr, size_t size, size_t nmemb, FILE*);
 int vprintf(const char* fmt, va_list) __attribute__((format(printf, 1, 0)));
 int vfprintf(FILE*, const char* fmt, va_list) __attribute__((format(printf, 2, 0)));