New file autoload.h that will ultimately handle autoloading completions and functions

autoload.cpp

@@ -0,0 +1,164 @@
+/** \file autoload.cpp
+	
+The classes responsible for autoloading functions and completions.
+*/
+
+#include "config.h"
+#include "autoload.h"
+#include "wutil.h"
+#include <assert.h>
+
+const size_t kLRULimit = 256;
+
+/** A node in our LRU map */
+class file_access_node_t {
+public:
+    file_access_node_t *prev, *next;
+    const wcstring path;
+    file_access_attempt_t attempt;
+    
+    file_access_node_t(const wcstring &pathVar) : path(pathVar) { }
+    
+    bool operator<(const file_access_node_t &other) const { return path < other.path; }
+};
+
+/* By default, things are stale after 60 seconds */
+const time_t kFishDefaultStalenessInterval = 60;
+
+access_tracker_t::access_tracker_t(time_t stale, int the_mode) :
+        node_count(0),
+        mouth(NULL),
+        stale_interval(stale),
+        mode(the_mode)
+{
+    VOMIT_ON_FAILURE(pthread_mutex_init(&lock, NULL));
+}
+
+access_tracker_t::~access_tracker_t() {
+    VOMIT_ON_FAILURE(pthread_mutex_destroy(&lock));
+}
+
+void access_tracker_t::vacuum_one_node(void) {
+    /* Removes the least recently used access */
+    assert(mouth && mouth->prev != mouth);
+    
+    /* Remove us from the linked list */
+    file_access_node_t *condemned_node = mouth->prev;
+    condemned_node->prev->next = condemned_node->next;
+    condemned_node->next->prev = condemned_node->prev;
+    
+    /* Remove us from the set */
+    access_set.erase(condemned_node);
+    
+    /* Deleted */
+    node_count--;
+    delete condemned_node;
+}
+
+void access_tracker_t::promote_node(file_access_node_t *node) {
+    /* Promotes a node to the mouth, unless we're already there... */
+    if (node == mouth) return;
+    
+    /* First unhook us */
+    node->prev->next = node->next;
+    node->next->prev = node->prev;
+    
+    /* Now become the mouth */
+    node->next = mouth;
+    node->prev = mouth->prev;
+    mouth = node;
+}
+
+/* Return the node referenced by the given string, or NULL */
+file_access_node_t *access_tracker_t::while_locked_find_node(const wcstring &path) const {
+    file_access_node_t key(path);
+    access_set_t::iterator iter = access_set.find(&key);
+    return iter != access_set.end() ? *iter : NULL;
+}
+
+file_access_attempt_t access_tracker_t::attempt_access(const wcstring& path) const {
+    file_access_attempt_t result = {0};
+    struct stat statbuf;
+    if (wstat(path.c_str(), &statbuf)) {
+        result.error = errno;
+    } else {
+        result.mod_time = statbuf.st_mtime;
+        if (waccess(path.c_str(), this->mode)) {
+            result.error = errno;
+        } else {
+            result.accessible = true;
+        }
+    }
+    
+    // Note that we record the last checked time after the call, on the assumption that in a slow filesystem, the lag comes before the kernel check, not after.
+    result.stale = false;
+    result.last_checked = time(NULL);
+    return result;
+}
+
+bool access_tracker_t::access_file_only_cached(const wcstring &path, file_access_attempt_t &attempt) {
+    bool result = false;
+    
+    /* Lock our lock */
+    scoped_lock locker(lock);
+    
+    /* Search for the node */
+    file_access_node_t *node = while_locked_find_node(path);
+    if (node) {
+        promote_node(node);
+        attempt = node->attempt;
+        attempt.stale = (time(NULL) - node->attempt.last_checked > this->stale_interval);
+        result = true;
+    }    
+    return result;
+}
+
+file_access_attempt_t access_tracker_t::access_file(const wcstring &path) {
+    file_access_attempt_t result;
+    
+    /* Try just using our cache */
+    if (access_file_only_cached(path, result) && ! result.stale) {
+        return result;
+    }
+    
+    /* Really access the file. Note we are not yet locked, and don't want to be, since this may be slow. */
+    result = attempt_access(path);
+    
+    /* Take the lock so we can insert. */
+    scoped_lock locker(lock);
+    
+    /* Maybe we had it cached and it was stale, or maybe someone else may have put it in the cache while we were unlocked */
+    file_access_node_t *node = while_locked_find_node(path);
+    
+    if (node != NULL) {
+        /* Someone else put it in. Promote and overwrite it. */
+        node->attempt = result;
+        promote_node(node);
+    } else {
+        /* We did not find this node. Add it. */
+        file_access_node_t *node = new file_access_node_t(path);
+        node->attempt = result;
+        
+        /* Insert into the set */
+        access_set.insert(node);
+        
+        /* Insert it into the linked list */
+        if (mouth == NULL) {
+            /* One element circularly linked list! */
+            mouth = node->next = node->prev = node;
+        } else {
+            /* Normal circularly linked list operation */
+            node->next = mouth;
+            node->prev = mouth->prev;
+            mouth = node;
+        }
+        
+        /* We have one more node now */
+        ++node_count;
+        
+        /* Clean up if we're over our limit */
+        while (node_count > kLRULimit)
+            vacuum_one_node();
+    }
+    return result;
+}