Make the memory-window conrol structures global

Up to now, the idea was that the user would do all the operations for
one repository in the same thread. Thus we could have the
memory-mapped window information thread-local and avoid any locking.

This is not practical in a few environments, such as Apple's GCD which
allocates threads arbitrarily or the .NET CLR, where the OS-level
thread can change at any moment.

Make the control structure global and protect it with a mutex so we
don't depend on the thread currently executing the code.

diff --git a/src/global.c b/src/global.c
index 368c6c664331ff824366d9d2ee72a772a3442fdd..691f0d4f6897ed5c781b1ada0a2e653ed9546357 100644 (file)
--- a/src/global.c
+++ b/src/global.c
@@ -9,6 +9,9 @@
 #include "git2/threads.h" 
 #include "thread-utils.h"
 
+
+git_mutex git__mwindow_mutex;
+
 /**
  * Handle the global state with TLS
  *
@@ -47,12 +50,14 @@ void git_threads_init(void)
 
        _tls_index = TlsAlloc();
        _tls_init = 1;
+       git_mutex_init(&git__mwindow_mutex);
 }
 
 void git_threads_shutdown(void)
 {
        TlsFree(_tls_index);
        _tls_init = 0;
+       git_mutex_free(&git__mwindow_mutex);
 }
 
 git_global_st *git__global_state(void)

diff --git a/src/global.h b/src/global.h
index 6e7373fa3d5b6bd8213a955adc3c7304a51fad92..0ad41ee63e58a3444b8acfc3f000d4ab0e21115f 100644 (file)
--- a/src/global.h
+++ b/src/global.h
@@ -12,12 +12,12 @@
 typedef struct {
        git_error *last_error;
        git_error error_t;
-
-       git_mwindow_ctl mem_ctl;
 } git_global_st;
 
 git_global_st *git__global_state(void);
 
+extern git_mutex git__mwindow_mutex;
+
 #define GIT_GLOBAL (git__global_state())
 
 #endif

diff --git a/src/mwindow.c b/src/mwindow.c
index 1a5446b9ccd25c830d55192a0c8d12ffcf648820..4da5badb626143194823f65254c9ef02a0c61e9c 100644 (file)
--- a/src/mwindow.c
+++ b/src/mwindow.c
@@ -32,14 +32,20 @@ static struct {
        DEFAULT_MAPPED_LIMIT,
 };
 
+/* Whenever you want to read or modify this, grab git__mwindow_mutex */
+static git_mwindow_ctl mem_ctl;
+
 /*
  * Free all the windows in a sequence, typically because we're done
  * with the file
  */
 void git_mwindow_free_all(git_mwindow_file *mwf)
 {
-       git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
+       git_mwindow_ctl *ctl = &mem_ctl;
        unsigned int i;
+
+       git_mutex_lock(&git__mwindow_mutex);
+
        /*
         * Remove these windows from the global list
         */
@@ -67,6 +73,8 @@ void git_mwindow_free_all(git_mwindow_file *mwf)
                mwf->windows = w->next;
                git__free(w);
        }
+
+       git_mutex_unlock(&git__mwindow_mutex);
 }
 
 /*
@@ -82,7 +90,7 @@ int git_mwindow_contains(git_mwindow *win, git_off_t offset)
 /*
  * Find the least-recently-used window in a file
  */
-void git_mwindow_scan_lru(
+static void git_mwindow_scan_lru(
        git_mwindow_file *mwf,
        git_mwindow **lru_w,
        git_mwindow **lru_l)
@@ -107,11 +115,12 @@ void git_mwindow_scan_lru(
 
 /*
  * Close the least recently used window. You should check to see if
- * the file descriptors need closing from time to time.
+ * the file descriptors need closing from time to time. Called under
+ * lock from new_window.
  */
 static int git_mwindow_close_lru(git_mwindow_file *mwf)
 {
-       git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
+       git_mwindow_ctl *ctl = &mem_ctl;
        unsigned int i;
        git_mwindow *lru_w = NULL, *lru_l = NULL, **list = &mwf->windows;
 
@@ -146,13 +155,14 @@ static int git_mwindow_close_lru(git_mwindow_file *mwf)
        return 0;
 }
 
+/* This gets called under lock from git_mwindow_open */
 static git_mwindow *new_window(
        git_mwindow_file *mwf,
        git_file fd,
        git_off_t size,
        git_off_t offset)
 {
-       git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
+       git_mwindow_ctl *ctl = &mem_ctl;
        size_t walign = _mw_options.window_size / 2;
        git_off_t len;
        git_mwindow *w;
@@ -208,9 +218,10 @@ unsigned char *git_mwindow_open(
        size_t extra,
        unsigned int *left)
 {
-       git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
+       git_mwindow_ctl *ctl = &mem_ctl;
        git_mwindow *w = *cursor;
 
+       git_mutex_lock(&git__mwindow_mutex);
        if (!w || !(git_mwindow_contains(w, offset) && git_mwindow_contains(w, offset + extra))) {
                if (w) {
                        w->inuse_cnt--;
@@ -228,8 +239,10 @@ unsigned char *git_mwindow_open(
                 */
                if (!w) {
                        w = new_window(mwf, mwf->fd, mwf->size, offset);
-                       if (w == NULL)
+                       if (w == NULL) {
+                               git_mutex_unlock(&git__mwindow_mutex);
                                return NULL;
+                       }
                        w->next = mwf->windows;
                        mwf->windows = w;
                }
@@ -247,32 +260,43 @@ unsigned char *git_mwindow_open(
        if (left)
                *left = (unsigned int)(w->window_map.len - offset);
 
+       git_mutex_unlock(&git__mwindow_mutex);
        return (unsigned char *) w->window_map.data + offset;
 }
 
 int git_mwindow_file_register(git_mwindow_file *mwf)
 {
-       git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
+       git_mwindow_ctl *ctl = &mem_ctl;
+       int ret;
 
+       git_mutex_lock(&git__mwindow_mutex);
        if (ctl->windowfiles.length == 0 &&
-               git_vector_init(&ctl->windowfiles, 8, NULL) < 0)
+           git_vector_init(&ctl->windowfiles, 8, NULL) < 0) {
+               git_mutex_unlock(&git__mwindow_mutex);
                return -1;
+       }
+
+       ret = git_vector_insert(&ctl->windowfiles, mwf);
+       git_mutex_unlock(&git__mwindow_mutex);
 
-       return git_vector_insert(&ctl->windowfiles, mwf);
+       return ret;
 }
 
 int git_mwindow_file_deregister(git_mwindow_file *mwf)
 {
-       git_mwindow_ctl *ctl = &GIT_GLOBAL->mem_ctl;
+       git_mwindow_ctl *ctl = &mem_ctl;
        git_mwindow_file *cur;
        unsigned int i;
 
+       git_mutex_lock(&git__mwindow_mutex);
        git_vector_foreach(&ctl->windowfiles, i, cur) {
                if (cur == mwf) {
                        git_vector_remove(&ctl->windowfiles, i);
+                       git_mutex_unlock(&git__mwindow_mutex);
                        return 0;
                }
        }
+       git_mutex_unlock(&git__mwindow_mutex);
 
        giterr_set(GITERR_ODB, "Failed to find the memory window file to deregister");
        return -1;
@@ -282,7 +306,9 @@ void git_mwindow_close(git_mwindow **window)
 {
        git_mwindow *w = *window;
        if (w) {
+               git_mutex_lock(&git__mwindow_mutex);
                w->inuse_cnt--;
+               git_mutex_unlock(&git__mwindow_mutex);
                *window = NULL;
        }
 }

diff --git a/src/mwindow.h b/src/mwindow.h
index d4fd195690513986c8210951ea19c7f7929a48f7..c5aeaf77b77b2dfd6aef7dc2e1ede41813e97313 100644 (file)
--- a/src/mwindow.h
+++ b/src/mwindow.h
@@ -38,7 +38,6 @@ typedef struct git_mwindow_ctl {
 int git_mwindow_contains(git_mwindow *win, git_off_t offset);
 void git_mwindow_free_all(git_mwindow_file *mwf);
 unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor, git_off_t offset, size_t extra, unsigned int *left);
-void git_mwindow_scan_lru(git_mwindow_file *mwf, git_mwindow **lru_w, git_mwindow **lru_l);
 int git_mwindow_file_register(git_mwindow_file *mwf);
 int git_mwindow_file_deregister(git_mwindow_file *mwf);
 void git_mwindow_close(git_mwindow **w_cursor);