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/**
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0.
*/
#include <aws/common/cross_process_lock.h>
#include <aws/common/byte_buf.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <unistd.h>
#include <aws/common/error.h>
#include <aws/common/file.h>
#include <aws/common/logging.h>
struct aws_cross_process_lock {
struct aws_allocator *allocator;
int locked_fd;
};
struct aws_cross_process_lock *aws_cross_process_lock_try_acquire(
struct aws_allocator *allocator,
struct aws_byte_cursor instance_nonce) {
/* validate we don't have a directory slash. */
struct aws_byte_cursor to_find = aws_byte_cursor_from_c_str("/");
struct aws_byte_cursor found;
AWS_ZERO_STRUCT(found);
if (aws_byte_cursor_find_exact(&instance_nonce, &to_find, &found) != AWS_OP_ERR &&
aws_last_error() != AWS_ERROR_STRING_MATCH_NOT_FOUND) {
AWS_LOGF_ERROR(
AWS_LS_COMMON_GENERAL,
"static: Lock " PRInSTR "creation has illegal character /",
AWS_BYTE_CURSOR_PRI(instance_nonce));
aws_raise_error(AWS_ERROR_INVALID_ARGUMENT);
return NULL;
}
/*
* The unix standard says /tmp has to be there and be writable. However, while it may be tempting to just use the
* /tmp/ directory, it often has the sticky bit set which would prevent a subprocess from being able to call open
* with create on the file. The solution is simple, just write it to a subdirectory inside
* /tmp and override umask via. chmod of 0777.
*/
struct aws_byte_cursor path_prefix = aws_byte_cursor_from_c_str("/tmp/aws_crt_cross_process_lock/");
struct aws_string *path_to_create = aws_string_new_from_cursor(allocator, &path_prefix);
/* It's probably there already and we don't care if it is. */
if (!aws_directory_exists(path_to_create)) {
/* if this call fails just let it fail on open below. */
aws_directory_create(path_to_create);
/* bypass umask by setting the perms we actually requested */
chmod(aws_string_c_str(path_to_create), S_IRWXU | S_IRWXG | S_IRWXO);
}
aws_string_destroy(path_to_create);
struct aws_byte_cursor path_suffix = aws_byte_cursor_from_c_str(".lock");
struct aws_byte_buf nonce_buf;
aws_byte_buf_init_copy_from_cursor(&nonce_buf, allocator, path_prefix);
aws_byte_buf_append_dynamic(&nonce_buf, &instance_nonce);
aws_byte_buf_append_dynamic(&nonce_buf, &path_suffix);
aws_byte_buf_append_null_terminator(&nonce_buf);
struct aws_cross_process_lock *instance_lock = NULL;
errno = 0;
int fd = open((const char *)nonce_buf.buffer, O_CREAT | O_RDWR, 0666);
if (fd < 0) {
AWS_LOGF_DEBUG(
AWS_LS_COMMON_GENERAL,
"static: Lock file %s failed to open with errno %d",
(const char *)nonce_buf.buffer,
errno);
aws_translate_and_raise_io_error_or(errno, AWS_ERROR_MUTEX_FAILED);
if (aws_last_error() == AWS_ERROR_NO_PERMISSION) {
AWS_LOGF_DEBUG(
AWS_LS_COMMON_GENERAL,
"static: Lock file %s couldn't be opened due to file ownership permissions. Attempting to open as read "
"only",
(const char *)nonce_buf.buffer);
errno = 0;
fd = open((const char *)nonce_buf.buffer, O_RDONLY);
if (fd < 0) {
AWS_LOGF_ERROR(
AWS_LS_COMMON_GENERAL,
"static: Lock file %s failed to open with read-only permissions with errno %d",
(const char *)nonce_buf.buffer,
errno);
aws_translate_and_raise_io_error_or(errno, AWS_ERROR_MUTEX_FAILED);
goto cleanup;
}
} else {
AWS_LOGF_ERROR(
AWS_LS_COMMON_GENERAL,
"static: Lock file %s failed to open. The lock cannot be acquired.",
(const char *)nonce_buf.buffer);
goto cleanup;
}
}
if (flock(fd, LOCK_EX | LOCK_NB) == -1) {
AWS_LOGF_TRACE(
AWS_LS_COMMON_GENERAL,
"static: Lock file %s already acquired by another instance",
(const char *)nonce_buf.buffer);
close(fd);
aws_raise_error(AWS_ERROR_MUTEX_CALLER_NOT_OWNER);
goto cleanup;
}
instance_lock = aws_mem_calloc(allocator, 1, sizeof(struct aws_cross_process_lock));
instance_lock->locked_fd = fd;
instance_lock->allocator = allocator;
AWS_LOGF_TRACE(
AWS_LS_COMMON_GENERAL,
"static: Lock file %s acquired by this instance with fd %d",
(const char *)nonce_buf.buffer,
fd);
cleanup:
aws_byte_buf_clean_up(&nonce_buf);
return instance_lock;
}
void aws_cross_process_lock_release(struct aws_cross_process_lock *instance_lock) {
if (instance_lock) {
flock(instance_lock->locked_fd, LOCK_UN);
close(instance_lock->locked_fd);
AWS_LOGF_TRACE(AWS_LS_COMMON_GENERAL, "static: Lock file released for fd %d", instance_lock->locked_fd);
aws_mem_release(instance_lock->allocator, instance_lock);
}
}
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