provide thread safety for the stdio routines

libc/stdio/__fdopen.c

@@ -50,7 +50,7 @@ FILE *__fdopen(int fd, const char *mode)
 	f->seek = __stdio_seek;
 	f->close = __stdio_close;
 
-	if (!libc.threaded) f->lock = -1;
+	if (!libc.threaded) f->lock_owner = STDIO_SINGLETHREADED;
 
 	/* Add new FILE to open file list */
 	OFLLOCK();

libc/stdio/__fopen_rb_ca.c

@@ -15,7 +15,7 @@ FILE *__fopen_rb_ca(const char *filename, FILE *f, unsigned char *buf, size_t le
 	f->read = __stdio_read;
 	f->seek = __stdio_seek;
 	f->close = __stdio_close;
-	f->lock = -1;
+	f->lock_owner = STDIO_SINGLETHREADED;
 
 	return f;
 }

libc/stdio/__lockfile.c

+#include <assert.h>
+#include <pthread.h>
 #include "stdio_impl.h"
-//#include "pthread_impl.h"
 
 int __lockfile(FILE *f)
 {
-#ifdef TODO
-	int owner, tid = __pthread_self()->tid;
-	if (f->lock == tid)
+	pthread_t self = pthread_self();
+	if (f->lock_owner == self)
 		return 0;
-	while ((owner = a_cas(&f->lock, 0, tid)))
-		__wait(&f->lock, &f->waiters, owner, 1);
-#endif
+	mutex_lock(&f->mutex);
+	f->lock_owner = self;
 	return 1;
 }
 
 void __unlockfile(FILE *f)
 {
-#ifdef TODO
-	a_store(&f->lock, 0);
-
-	/* The following read is technically invalid under situations
-	 * of self-synchronized destruction. Another thread may have
-	 * called fclose as soon as the above store has completed.
-	 * Nonetheless, since FILE objects always live in memory
-	 * obtained by malloc from the heap, it's safe to assume
-	 * the dereferences below will not fault. In the worst case,
-	 * a spurious syscall will be made. If the implementation of
-	 * malloc changes, this assumption needs revisiting. */
-
-	if (f->waiters) __wake(&f->lock, 1, 1);
-#endif
+	assert(f->lock_owner == pthread_self());
+	f->lock_owner = 0;
+	mutex_unlock(&f->mutex);
 }

libc/stdio/fgetc.c

@@ -3,7 +3,7 @@
 int fgetc(FILE *f)
 {
 	int c;
-	if (f->lock < 0 || !__lockfile(f))
+	if (f->lock_owner == STDIO_SINGLETHREADED || !__lockfile(f))
 		return getc_unlocked(f);
 	c = getc_unlocked(f);
 	__unlockfile(f);

libc/stdio/fmemopen.c

@@ -109,7 +109,7 @@ FILE *fmemopen(void *restrict buf, size_t size, const char *restrict mode)
 	f->seek = mseek;
 	f->close = mclose;
 
-	if (!libc.threaded) f->lock = -1;
+	if (!libc.threaded) f->lock_owner = STDIO_SINGLETHREADED;
 
 	OFLLOCK();
 	f->next = libc.ofl_head;

libc/stdio/fputc.c

@@ -2,7 +2,7 @@
 
 int fputc(int c, FILE *f)
 {
-	if (f->lock < 0 || !__lockfile(f))
+	if (f->lock_owner == STDIO_SINGLETHREADED || !__lockfile(f))
 		return putc_unlocked(c, f);
 	c = putc_unlocked(c, f);
 	__unlockfile(f);

libc/stdio/getc.c

@@ -3,7 +3,7 @@
 int getc(FILE *f)
 {
 	int c;
-	if (f->lock < 0 || !__lockfile(f))
+	if (f->lock_owner == STDIO_SINGLETHREADED || !__lockfile(f))
 		return getc_unlocked(f);
 	c = getc_unlocked(f);
 	__unlockfile(f);

libc/stdio/open_memstream.c

@@ -78,7 +78,7 @@ FILE *open_memstream(char **bufp, size_t *sizep)
 	f->seek = ms_seek;
 	f->close = ms_close;
 
-	if (!libc.threaded) f->lock = -1;
+	if (!libc.threaded) f->lock_owner = STDIO_SINGLETHREADED;
 
 	OFLLOCK();
 	f->next = libc.ofl_head;

libc/stdio/open_wmemstream.c

@@ -79,7 +79,7 @@ FILE *open_wmemstream(wchar_t **bufp, size_t *sizep)
 	f->seek = wms_seek;
 	f->close = wms_close;
 
-	if (!libc.threaded) f->lock = -1;
+	if (!libc.threaded) f->lock_owner = STDIO_SINGLETHREADED;
 
 	OFLLOCK();
 	f->next = libc.ofl_head;

libc/stdio/putc.c

@@ -2,7 +2,7 @@
 
 int putc(int c, FILE *f)
 {
-	if (f->lock < 0 || !__lockfile(f))
+	if (f->lock_owner == STDIO_SINGLETHREADED || !__lockfile(f))
 		return putc_unlocked(c, f);
 	c = putc_unlocked(c, f);
 	__unlockfile(f);

libc/stdio/stderr.c

@@ -10,7 +10,7 @@ static FILE f = {
 	.write = __stdio_write,
 	.seek = __stdio_seek,
 	.close = __stdio_close,
-	.lock = -1,
+	.lock_owner = STDIO_SINGLETHREADED,
 };
 FILE *const stderr = &f;
 FILE *const __stderr_used = &f;

libc/stdio/stdin.c

@@ -9,7 +9,7 @@ static FILE f = {
 	.read = __stdio_read,
 	.seek = __stdio_seek,
 	.close = __stdio_close,
-	.lock = -1,
+	.lock_owner = STDIO_SINGLETHREADED,
 };
 FILE *const stdin = &f;
 FILE *const __stdin_used = &f;

libc/stdio/stdio_impl.h

@@ -6,8 +6,10 @@
 
 #define UNGET 8
 
-#define FFINALLOCK(f) ((f)->lock>=0 ? __lockfile((f)) : 0)
-#define FLOCK(f) int __need_unlock = ((f)->lock>=0 ? __lockfile((f)) : 0)
+#define FFINALLOCK(f) \
+	((f)->lock_owner != STDIO_SINGLETHREADED ? __lockfile((f)) : 0)
+#define FLOCK(f) \
+	int __need_unlock = ((f)->lock_owner != STDIO_SINGLETHREADED ? __lockfile((f)) : 0)
 #define FUNLOCK(f) if (__need_unlock) __unlockfile((f)); else
 
 #define F_PERM 1
@@ -17,6 +19,15 @@
 #define F_ERR 32
 #define F_SVB 64
 
+/*
+ * Note: this structure is layed out so that the fields which are accessed
+ * by the unlocked getc/putc macros is identical to glibc.  Make sure to
+ * consult glibc before changing the layout of any fields.  Adding new fields
+ * should be generally okay.
+ *
+ * See musl commit e3cd6c5c265cd481db6e0c5b529855d99f0bda30 for some more
+ * details.
+ */
 struct __FILE_s {
 	unsigned flags;
 	unsigned char *rpos, *rend;
@@ -36,7 +47,7 @@ struct __FILE_s {
 	short dummy3;
 	signed char mode;
 	signed char lbf;
-	int lock;
+	int dummy4;
 	int waiters;
 	void *cookie;
 	off_t off;
@@ -44,6 +55,15 @@ struct __FILE_s {
 	void *mustbezero_2;
 	unsigned char *shend;
 	off_t shlim, shcnt;
+
+	/*
+	 * Using magic -1 and 0 values for pthread_t fields is a dangerous
+	 * game, but with our implementation of pthread_t as a pointer
+	 * we'll get away with it for now.
+	 */
+#define STDIO_SINGLETHREADED	((pthread_t)-1)
+	pthread_t lock_owner;
+	mutex_t mutex;
 };
 
 size_t __stdio_read(FILE *, unsigned char *, size_t);

libc/stdio/stdout.c

@@ -10,7 +10,7 @@ static FILE f = {
 	.write = __stdout_write,
 	.seek = __stdio_seek,
 	.close = __stdio_close,
-	.lock = -1,
+	.lock_owner = STDIO_SINGLETHREADED,
 };
 FILE *const stdout = &f;
 FILE *const __stdout_used = &f;

libc/stdio/vdprintf.c

@@ -10,7 +10,7 @@ int vdprintf(int fd, const char *restrict fmt, va_list ap)
 	FILE f = {
 		.fd = fd, .lbf = EOF, .write = wrap_write,
 		.buf = (void *)fmt, .buf_size = 0,
-		.lock = -1
+		.lock_owner = STDIO_SINGLETHREADED,
 	};
 	return vfprintf(&f, fmt, ap);
 }

libc/stdio/vsnprintf.c

@@ -18,7 +18,7 @@ int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list ap)
 {
 	int r;
 	char b;
-	FILE f = { .lbf = EOF, .write = sn_write, .lock = -1 };
+	FILE f = { .lbf = EOF, .write = sn_write, .lock_owner = STDIO_SINGLETHREADED };
 
 	if (n-1 > INT_MAX-1) {
 		if (n) {

libc/stdio/vsscanf.c

@@ -9,7 +9,7 @@ int vsscanf(const char *restrict s, const char *restrict fmt, va_list ap)
 {
 	FILE f = {
 		.buf = (void *)s, .cookie = (void *)s,
-		.read = do_read, .lock = -1
+		.read = do_read, .lock_owner = STDIO_SINGLETHREADED,
 	};
 	return vfscanf(&f, fmt, ap);
 }

libc/stdio/vswprintf.c

@@ -39,7 +39,7 @@ int vswprintf(wchar_t *restrict s, size_t n, const wchar_t *restrict fmt, va_lis
 	f.write = sw_write;
 	f.buf_size = sizeof buf;
 	f.buf = buf;
-	f.lock = -1;
+	f.lock_owner = STDIO_SINGLETHREADED;
 	f.cookie = &c;
 	if (!n) {
 		return -1;

libc/stdio/vswscanf.c

@@ -30,7 +30,7 @@ int vswscanf(const wchar_t *restrict s, const wchar_t *restrict fmt, va_list ap)
 	FILE f = {
 		.buf = buf, .buf_size = sizeof buf,
 		.cookie = (void *)s,
-		.read = wstring_read, .lock = -1
+		.read = wstring_read, .lock_owner = STDIO_SINGLETHREADED,
 	};
 	return vfwscanf(&f, fmt, ap);
 }

libc/stdlib/strtod.c

@@ -7,7 +7,7 @@ static long double strtox(const char *s, char **p, int prec)
 {
 	FILE f = {
 		.buf = (void *)s, .rpos = (void *)s,
-		.rend = (void *)-1, .lock = -1
+		.rend = (void *)-1, .lock_owner = STDIO_SINGLETHREADED,
 	};
 	shlim(&f, 0);
 	long double y = __floatscan(&f, prec, 1);