Changes to sort the results to readdir from the PAL layer on POSIX

The recent update of Mono changed the behavior of classlib file listing
apis such as Directory.GetFiles. In the past the results were sorted
alphabetically.

The implementation was moved to the pal/mono-native library and makes
use of readdir which does not guarantee any order.

We are trading some memory and speed to bring back the sorted behavior.
However the number are an improvement over the old glib implementation
we were using.

The downside is that programs that use enumerators.first or .any do not
perform as well as we are paying the price to sort the whole list.

Author: bholmes

external/corefx-bugfix/src/Native/Unix/System.Native/pal_io.c

@@ -363,14 +363,14 @@ static void ConvertDirent(const struct dirent* entry, struct DirectoryEntry* out
 #endif
 }
 
-#if HAVE_READDIR_R
+#if IL2CPP_HAVE_READDIR_R_DEPRECATED_DO_NOT_USE
 // struct dirent typically contains 64-bit numbers (e.g. d_ino), so we align it at 8-byte.
 static const size_t dirent_alignment = 8;
 #endif
 
 int32_t SystemNative_GetReadDirRBufferSize(void)
 {
-#if HAVE_READDIR_R
+#if IL2CPP_HAVE_READDIR_R_DEPRECATED_DO_NOT_USE
     // dirent should be under 2k in size
     assert(sizeof(struct dirent) < 2048);
     // add some extra space so we can align the buffer to dirent.
@@ -380,17 +380,25 @@ int32_t SystemNative_GetReadDirRBufferSize(void)
 #endif
 }
 
+#if READDIR_SORT
+static int cmpstring(const void *p1, const void *p2)
+{
+    return strcmp(((struct dirent*) p1)->d_name, ((struct dirent*) p2)->d_name);
+}
+#endif
+
 // To reduce the number of string copies, the caller of this function is responsible to ensure the memory
 // referenced by outputEntry remains valid until it is read.
 // If the platform supports readdir_r, the caller provides a buffer into which the data is read.
 // If the platform uses readdir, the caller must ensure no calls are made to readdir/closedir since those will invalidate
 // the current dirent. We assume the platform supports concurrent readdir calls to different DIRs.
-int32_t SystemNative_ReadDirR(DIR* dir, uint8_t* buffer, int32_t bufferSize, struct DirectoryEntry* outputEntry)
+int32_t SystemNative_ReadDirR(struct DIRWrapper* dirWrapper, uint8_t* buffer, int32_t bufferSize, struct DirectoryEntry* outputEntry)
 {
-    assert(dir != NULL);
+    assert(dirWrapper != NULL);
+    assert(dirWrapper->dir != NULL);
     assert(outputEntry != NULL);
 
-#if HAVE_READDIR_R
+#if IL2CPP_HAVE_READDIR_R_DEPRECATED_DO_NOT_USE
     assert(buffer != NULL);
 
     // align to dirent
@@ -445,7 +453,48 @@ int32_t SystemNative_ReadDirR(DIR* dir, uint8_t* buffer, int32_t bufferSize, str
     (void)buffer;     // unused
     (void)bufferSize; // unused
     errno = 0;
-    struct dirent* entry = readdir(dir);
+
+#if READDIR_SORT
+    struct dirent* entry;
+
+    if (!dirWrapper->result)
+    {
+        size_t numEntries = 0;
+        while ((entry = readdir(dirWrapper->dir))) numEntries++;
+        if (numEntries)
+        {
+            dirWrapper->result = malloc(numEntries * sizeof(struct dirent));
+            dirWrapper->curIndex = 0;
+            dirWrapper->numEntries = numEntries;
+#if HAVE_REWINDDIR
+            rewinddir (dirWrapper->dir);
+#else
+            closedir(dirWrapper->dir);
+            dirWrapper->dir = opendir(dirWrapper->dirPath);
+#endif
+            size_t index = 0;
+            while ((entry = readdir(dirWrapper->dir)))
+            {
+                memcpy(&((struct dirent*)dirWrapper->result)[index], entry, sizeof(struct dirent));
+                index++;
+            }
+
+            qsort(dirWrapper->result, numEntries, sizeof(struct dirent), cmpstring);
+        }
+    }
+
+    if (dirWrapper->curIndex < dirWrapper->numEntries)
+    {
+        entry = &((struct dirent*)dirWrapper->result)[dirWrapper->curIndex];
+        dirWrapper->curIndex++;
+    }
+
+    else
+        entry = NULL;
+
+#else
+    struct dirent* entry = readdir(dirWrapper->dir);
+#endif
 
     // 0 returned with null result -> end-of-stream
     if (entry == NULL)
@@ -465,14 +514,41 @@ int32_t SystemNative_ReadDirR(DIR* dir, uint8_t* buffer, int32_t bufferSize, str
     return 0;
 }
 
-DIR* SystemNative_OpenDir(const char* path)
+struct DIRWrapper* SystemNative_OpenDir(const char* path)
 {
-    return opendir(path);
+    DIR* dir = opendir(path);
+
+    if (dir == NULL)
+        return NULL;
+
+    struct DIRWrapper* ret = (struct DIRWrapper*)malloc(sizeof(struct DIRWrapper));
+    ret->dir = dir;
+#if READDIR_SORT
+    ret->result = NULL;
+    ret->curIndex = 0;
+    ret->numEntries = 0;
+#if !HAVE_REWINDDIR
+    ret->dirPath = strdup(path);
+#endif
+#endif
+    return ret;
 }
 
-int32_t SystemNative_CloseDir(DIR* dir)
+int32_t SystemNative_CloseDir(struct DIRWrapper* dirWrapper)
 {
-    return closedir(dir);
+    assert(dirWrapper != NULL);
+    int32_t ret = closedir(dirWrapper->dir);
+#if READDIR_SORT
+    if (dirWrapper->result)
+        free (dirWrapper->result);
+    dirWrapper->result = NULL;
+#if !HAVE_REWINDDIR
+    if (dirWrapper->dirPath)
+        free(dirWrapper->dirPath);
+#endif
+    free(dirWrapper);
+#endif
+    return ret;
 }
 
 int32_t SystemNative_Pipe(int32_t pipeFds[2], int32_t flags)

external/corefx-bugfix/src/Native/Unix/System.Native/pal_io.h

@@ -338,6 +338,21 @@ enum NotifyEvents
     PAL_IN_ISDIR = 0x40000000,
 };
 
+#define READDIR_SORT 1
+
+struct DIRWrapper
+{
+    DIR* dir;
+#if READDIR_SORT
+    void* result;
+    size_t curIndex;
+    size_t numEntries;
+#if !HAVE_REWINDDIR
+    char* dirPath;
+#endif
+#endif
+};
+
 
 int32_t SystemNative_Stat2(const char* path, struct FileStatus* output);
 int32_t SystemNative_FStat2(intptr_t fd, struct FileStatus* output);
@@ -416,17 +431,17 @@ DLLEXPORT int32_t SystemNative_GetReadDirRBufferSize(void);
  *
  * Returns 0 when data is retrieved; returns -1 when end-of-stream is reached; returns an error code on failure
  */
-DLLEXPORT int32_t SystemNative_ReadDirR(DIR* dir, uint8_t* buffer, int32_t bufferSize, struct DirectoryEntry* outputEntry);
+DLLEXPORT int32_t SystemNative_ReadDirR(struct DIRWrapper* dirWrapper, uint8_t* buffer, int32_t bufferSize, struct DirectoryEntry* outputEntry);
 
 /**
  * Returns a DIR struct containing info about the current path or NULL on failure; sets errno on fail.
  */
-DLLEXPORT DIR* SystemNative_OpenDir(const char* path);
+DLLEXPORT struct DIRWrapper* SystemNative_OpenDir(const char* path);
 
 /**
  * Closes the directory stream opened by opendir and returns 0 on success. On fail, -1 is returned and errno is set
  */
-DLLEXPORT int32_t SystemNative_CloseDir(DIR* dir);
+DLLEXPORT int32_t SystemNative_CloseDir(struct DIRWrapper* dirWrapper);
 
 /**
  * Creates a pipe. Implemented as shim to pipe(2) or pipe2(2) if available.